US20140010968A1

US20140010968A1 - Flame sprayed bulk solidifying amorphous alloy cladding layer

Info

Publication number: US20140010968A1
Application number: US13/541,693
Authority: US
Inventors: Christopher D. Prest; Matthew S. Scott; Stephen P. Zadesky; Dermot J. Stratton; Joseph C. Poole; Lucy E. Browning
Original assignee: Apple Inc
Current assignee: Apple Inc
Priority date: 2012-07-04
Filing date: 2012-07-04
Publication date: 2014-01-09

Abstract

Disclosed is a method of coating a substrate with a bulk-solidifying amorphous alloy using a thermal spraying technique to provide a coating that is substantially amorphous. Some embodiments include using a substrate having a thickness greater than the critical casting thickness of the bulk-solidifying amorphous alloy, and using a brazing material to assist in adhering the coating to the surface.

Description

All publications, patents, and patent applications cited in this Specification are hereby incorporated by reference in their entirety.

BACKGROUND

Numerous ferrous alloys (e.g., high strength steels) and non-ferrous alloys have been developed for use in heavy construction and machinery. Although these alloys provide a good combination of strength and toughness, they typically do not show adequate resistance to wear, erosion, and corrosion. Thus, they are not well-suited for use in applications in which the surfaces of these alloys are subjected to aggressive environment or abrasion. One approach to remedy this problem is to use a hard-facing material deposited onto the surface of an underlying structure/substrate to act as a protective layer. The underlying structure (e.g., steel substrate) provides the strength and structural integrity needed for the layer-substrate structure, and the hard-facing alloy protects the substrate against wear and abrasion in adverse environments. The hard-facing material also can protect the substrate against corrosion as well.
A wide-variety of hard-facing materials are known, including, for example, ceramic-containing compositions such as tungsten carbide/cobalt and purely metallic compositions. One problem encountered with most hard-facing material is that when applied by thermal spraying, the hard-facing deposit often contains porosity and has through-cracks that extend perpendicularly to the thickness direction of the coating. The porosity permits corrosive media to penetrate through the coating to reach the substrate and damage it by chemical corrosion or stress corrosion. The through-cracks can also lead to fracturing and spalling of the wear-resistant coating, thereby resulting in the abrasive or corrosive media reaching the underlying substrate and rapidly wearing out the underlying substrate.
Another class of metallic hard-facing materials is the frictionally transforming amorphous alloys generally disclosed in U.S. Pat. No. 4,725,512. These ferrous materials can be deposited upon the surface of a substrate as a hard-facing layer in their non-amorphous state by techniques such as thermal spraying. When the hard-facing layer is subjected to wearing forces, such as abrasive wear, the deposited material can metamorphically transform to a hard, wear-resistant amorphous state. Another class of alloys is titanium-containing ferrous hard-facing material, which are disclosed in U.S. Pat. No. 5,695,825. Although these hard-facing alloys are suitable for certain applications and used extensively as coatings in drill-pipes, improvements are still desired.
International patent application No. PCT/US2011/029092, filed Mar. 18, 2011, and entitled “Molybdenum-based thermal spray powder and method of making the same,” the disclosure of which is incorporated by reference herein in its entirety, discloses a molybdenum-containing ferrous alloy useful in an improved thermal spray deposition technique. The method includes depositing a powder alloy composition onto a substrate to form a coating having improved hard-facing properties and thermal conductivity. This application and the previously-issued patents disclosing hard-facing alloys and methods of coating devices with the same provide metamorphically transformable coatings that transform into a hard, more wear-resistant state upon being subjected to wearing forces, such as abrasive wear. The abrasive wear, and resulting transformation of the coating, however, may cause the coating to have defects in certain areas, or become disassociated with the underlying material that it coats.
Flame spraying powders of metals, plastics, ceramics, and alloys to provide surface coatings is known and described in, for example, U.S. Pat. Nos. 6,168,090, 5,441,554, 5,019,686, 4,507,151, 4,361,604, 4,348,434, 4,348,433, 4,263,353, 4,230,749, 4,230,748, and 4,230,744, in U.S. Patent Application Publication Nos. 2005/0123686, 2008/0248222, 2009/0074955, 2009/0130841, and 2011/0064963, and in WO2008/076953, the disclosures of which are incorporated herein by reference in their entireties. Thermal spray processing is a technique used to apply a coating onto a substrate material. Often, the coating material is used to give the substrate enhanced surface properties. Also, the technique can be used to repair the substrate after damage or improper machining. Techniques for thermal spray processing involve using a spray gun to impart the coating material with a sufficient amount of energy such that it impacts and sticks via a mechanical bond. In these processes, molten or semi-molten droplets or particles of the coating material are impacted with the substrate material. Once deposited, these droplets or particles are often called “splats” owing to the plate-like appearance of the deposited particles. In many cases, the surface of the substrate is prepared by sandblasting to create asperities on the surface for the coating material to attach to. Some porosity in the coating may occur, and typically is a function of the material, spray parameters, and technique used (HVOF, plasma, combustion, TWAS, etc.).
Bulk-solidifying amorphous alloys, or bulk metallic glasses (“BMG”), are a recently developed class of metallic materials. These alloys may be solidified and cooled at relatively slow rates, and they retain the amorphous, non-crystalline (i.e., glassy) state at room temperature. This amorphous state can be highly advantageous for certain applications. If the cooling rate is not sufficiently high, crystals may form inside the alloy during cooling, so that the benefits of the amorphous state are partially or completely lost. For example, one risk with the creation of bulk amorphous alloy parts is partial crystallization due to either slow cooling or impurities in the raw material.
Bulk-solidifying amorphous alloys have been made in a variety of metallic systems. They are generally prepared by quenching from above the melting temperature to the ambient temperature. Generally, high cooling rates such as one on the order of 10⁵° C./sec, are needed to achieve an amorphous structure. The lowest rate by which a bulk solidifying alloy can be cooled to avoid crystallization, thereby achieving and maintaining the amorphous structure during cooling, is referred to as the “critical cooling rate” for the alloy. In order to achieve a cooling rate higher than the critical cooling rate, heat has to be extracted from the sample. Thus, the thickness of articles made from amorphous alloys often becomes a limiting dimension, which is generally referred to as the “critical (casting) thickness.” A critical thickness of an amorphous alloy can be obtained by heat-flow calculations, taking into account the critical cooling rate.
Thus, there is a need to overcome the aforedescribed challenges in a manner that does not adversely affect the basic operability of these materials.

SUMMARY

Provided in one embodiment is a method of coating a substrate with a bulk-solidifying amorphous alloy using a flame spraying method in which the substrate has a thickness greater than the critical casting thickness of the bulk-solidifying amorphous alloy. In accordance with one embodiment, there is provided a method of coating a substrate with a bulk-solidifying amorphous alloy that includes thermal spraying a bulk-solidifying amorphous alloy on at least one surface of a substrate having a thickness greater than the critical casting thickness of the bulk-solidifying amorphous alloy, and at a temperature cool enough that the sprayed alloy cools fast enough to avoid crystallization, thereby providing a substrate coated with the bulk-solidifying amorphous alloy in substantially amorphous form.
Provided in another embodiment is a method of coating a substrate with a bulk-solidifying amorphous alloy using a flame spraying method in which the substrate has a thickness greater than the critical casting thickness of the bulk-solidifying amorphous alloy. In accordance with one embodiment, there is provided a method of coating a substrate with a bulk-solidifying amorphous alloy that includes providing a powder alloy composition of a bulk-solidifying amorphous alloy to a thermal spray apparatus, thermally spraying a relatively uniform coating of the bulk-solidifying amorphous alloy onto at least a surface of the substrate such that the coating layer cools sufficiently rapidly to maintain the amorphous characteristic of the bulk-solidifying amorphous alloy, thereby providing a substrate coated with a substantially amorphous bulk-solidifying amorphous alloy.
Provided in another embodiment is a method of coating a substrate with a bulk-solidifying amorphous alloy that includes depositing a brazing layer on the substrate, optionally heating the substrate to fuse the brazing layer to the substrate and subsequently cooling the substrate and brazing later, thermal spraying a bulk-solidifying amorphous alloy on at least one surface of a substrate having a thickness greater than the critical casting thickness of the bulk-solidifying amorphous alloy to provide a substrate coated with a substantially amorphous bulk-solidifying amorphous alloy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 provides a temperature-viscosity diagram of an exemplary bulk solidifying amorphous alloy.

FIG. 2 provides a schematic of a time-temperature-transformation (TTT) diagram for an exemplary bulk solidifying amorphous alloy.

FIG. 3 shows a schematic diagram of an HVOF process for coating a bulk-solidifying amorphous alloy onto a substrate in accordance with one embodiment.

FIG. 4 shows a schematic diagram of a plasma thermal spray process for coating a bulk-solidifying amorphous alloy onto a substrate in accordance with another embodiment.

FIG. 5 is a graph showing the relationship between critical cooling rate, critical casting thickness and temperature interval for a variety of alloy materials.

DETAILED DESCRIPTION

All publications, patents, and patent applications cited in this Specification are hereby incorporated by reference in their entirety.
The articles “a” and “an” are used herein to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article. By way of example, “a polymer resin” means one polymer resin or more than one polymer resin. Any ranges cited herein are inclusive. The terms “substantially” and “about” used throughout this Specification are used to describe and account for small fluctuations. For example, they can refer to less than or equal to ±5%, such as less than or equal to ±2%, such as less than or equal to ±1%, such as less than or equal to ±0.5%, such as less than or equal to ±0.2%, such as less than or equal to ±0.1%, such as less than or equal to ±0.05%.
Bulk-solidifying amorphous alloys, or bulk metallic glasses (“BMG”), are a recently developed class of metallic materials. These alloys may be solidified and cooled at relatively slow rates, and they retain the amorphous, non-crystalline (i.e., glassy) state at room temperature. Amorphous alloys have many superior properties than their crystalline counterparts. However, if the cooling rate is not sufficiently high, crystals may form inside the alloy during cooling, so that the benefits of the amorphous state can be lost. For example, one challenge with the fabrication of bulk amorphous alloy parts is partial crystallization of the parts due to either slow cooling or impurities in the raw alloy material. As a high degree of amorphicity (and, conversely, a low degree of crystallinity) is desirable in BMG parts, there is a need to develop methods for casting BMG parts having controlled amount of amorphicity.
FIG. 1 (obtained from U.S. Pat. No. 7,575,040) shows a viscosity-temperature graph of an exemplary bulk solidifying amorphous alloy, from the VIT-001 series of Zr—Ti—Ni—Cu—Be family manufactured by Liquidmetal Technology. It should be noted that there is no clear liquid/solid transformation for a bulk solidifying amorphous metal during the formation of an amorphous solid. The molten alloy becomes more and more viscous with increasing undercooling until it approaches solid form around the glass transition temperature. Accordingly, the temperature of solidification front for bulk solidifying amorphous alloys can be around glass transition temperature, where the alloy will practically act as a solid for the purposes of pulling out the quenched amorphous sheet product.
FIG. 2 (obtained from U.S. Pat. No. 7,575,040) shows the time-temperature-transformation (TTT) cooling curve of an exemplary bulk solidifying amorphous alloy, or TTT diagram. Bulk-solidifying amorphous metals do not experience a liquid/solid crystallization transformation upon cooling, as with conventional metals. Instead, the highly fluid, non crystalline form of the metal found at high temperatures (near a “melting temperature” Tm) becomes more viscous as the temperature is reduced (near to the glass transition temperature Tg), eventually taking on the outward physical properties of a conventional solid.
Even though there is no liquid/crystallization transformation for a bulk solidifying amorphous metal, a “melting temperature” Tm may be defined as the thermodynamic liquidus temperature of the corresponding crystalline phase. Under this regime, the viscosity of bulk-solidifying amorphous alloys at the melting temperature could lie in the range of about 0.1 poise to about 10,000 poise, and even sometimes under 0.01 poise. A lower viscosity at the “melting temperature” would provide faster and complete filling of intricate portions of the shell/mold with a bulk solidifying amorphous metal for forming the BMG parts. Furthermore, the cooling rate of the molten metal to form a BMG part has to such that the time-temperature profile during cooling does not traverse through the nose-shaped region bounding the crystallized region in the TTT diagram of FIG. 2. In FIG. 2, Tnose is the critical crystallization temperature Tx where crystallization is most rapid and occurs in the shortest time scale.
The supercooled liquid region, the temperature region between Tg and Tx is a manifestation of the extraordinary stability against crystallization of bulk solidification alloys. In this temperature region the bulk solidifying alloy can exist as a high viscous liquid. The viscosity of the bulk solidifying alloy in the supercooled liquid region can vary between 1012 Pa s at the glass transition temperature down to 105 Pa s at the crystallization temperature, the high temperature limit of the supercooled liquid region. Liquids with such viscosities can undergo substantial plastic strain under an applied pressure. The embodiments herein make use of the large plastic formability in the supercooled liquid region as a forming and separating method.
One needs to clarify something about Tx. Technically, the nose-shaped curve shown in the TTT diagram describes Tx as a function of temperature and time. Thus, regardless of the trajectory that one takes while heating or cooling a metal alloy, when one hits the TTT curve, one has reached Tx. In FIG. 2, Tx is shown as a dashed line as Tx can vary from close to Tm to close to Tg.
The schematic TTT diagram of FIG. 2 shows processing methods of die casting from at or above Tm to below Tg without the time-temperature trajectory (shown as (1) as an example trajectory) hitting the TTT curve. During die casting, the forming takes place substeantially simultaneously with fast cooling to avoid the trajectory hitting the TTT curve. The processing methods for superplastic forming (SPF) from at or below Tg to below Tm without the time-temperature trajectory (shown as (2), (3) and (4) as example trajectories) hitting the TTT curve. In SPF, the amorphous BMG is reheated into the supercooled liquid region where the available processing window could be much larger than die casting, resulting in better controllability of the process. The SPF process does not require fast cooling to avoid crystallization during cooling. Also, as shown by example trajectories (2), (3) and (4), the SPF can be carried out with the highest temperature during SPF being above Tnose or below Tnose, up to about Tm. If one heats up a piece of amorphous alloy but manages to avoid hitting the TTT curve, you have heated “between Tg and Tm”, but one would have not reached Tx.
Typical differential scanning calorimeter (DSC) heating curves of bulk-solidifying amorphous alloys taken at a heating rate of 20 C/min describe, for the most part, a particular trajectory across the TTT data where one would likely see a Tg at a certain temperature, a Tx when the DSC heating ramp crosses the TTT crystallization onset, and eventually melting peaks when the same trajectory crosses the temperature range for melting. If one heats a bulk-solidifying amorphous alloy at a rapid heating rate as shown by the ramp up portion of trajectories (2), (3) and (4) in FIG. 2, then one could avoid the ITT curve entirely, and the DSC data would show a glass transition but no Tx upon heating. Another way to think about it is trajectories (2), (3) and (4) can fall anywhere in temperature between the nose of the TTT curve (and even above it) and the Tg line, as long as it does not hit the crystallization curve. That just means that the horizontal plateau in trajectories might get much shorter as one increases the processing temperature.

Phase

The term “phase” herein can refer to one that can be found in a thermodynamic phase diagram. A phase is a region of space (e.g., a thermodynamic system) throughout which all physical properties of a material are essentially uniform. Examples of physical properties include density, index of refraction, chemical composition and lattice periodicity. A simple description of a phase is a region of material that is chemically uniform, physically distinct, and/or mechanically separable. For example, in a system consisting of ice and water in a glass jar, the ice cubes are one phase, the water is a second phase, and the humid air over the water is a third phase. The glass of the jar is another separate phase. A phase can refer to a solid solution, which can be a binary, tertiary, quaternary, or more, solution, or a compound, such as an intermetallic compound. As another example, an amorphous phase is distinct from a crystalline phase.

Metal, Transition Metal, and Non-Metal

The term “metal” refers to an electropositive chemical element. The term “element” in this Specification refers generally to an element that can be found in a Periodic Table. Physically, a metal atom in the ground state contains a partially filled band with an empty state close to an occupied state. The term “transition metal” is any of the metallic elements within Groups 3 to 12 in the Periodic Table that have an incomplete inner electron shell and that serve as transitional links between the most and the least electropositive in a series of elements. Transition metals are characterized by multiple valences, colored compounds, and the ability to form stable complex ions. The term “nonmetal” refers to a chemical element that does not have the capacity to lose electrons and form a positive ion.
Depending on the application, any suitable nonmetal elements, or their combinations, can be used. The alloy (or “alloy composition”) can comprise multiple nonmetal elements, such as at least two, at least three, at least four, or more, nonmetal elements. A nonmetal element can be any element that is found in Groups 13-17 in the Periodic Table. For example, a nonmetal element can be any one of F, Cl, Br, I, At, O, S, Se, Te, Po, N, P, As, Sb, Bi, C, Si, Ge, Sn, Pb, and B. Occasionally, a nonmetal element can also refer to certain metalloids (e.g., B, Si, Ge, As, Sb, Te, and Po) in Groups 13-17. In one embodiment, the nonmetal elements can include B, Si, C, P, or combinations thereof. Accordingly, for example, the alloy can comprise a boride, a carbide, or both.
A transition metal element can be any of scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, yttrium, zirconium, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, silver, cadmium, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, mercury, rutherfordium, dubnium, seaborgium, bohrium, hassium, meitnerium, ununnilium, unununium, and ununbium. In one embodiment, a BMG containing a transition metal element can have at least one of Sc, Y, La, Ac, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Tc, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, and Hg. Depending on the application, any suitable transitional metal elements, or their combinations, can be used. The alloy composition can comprise multiple transitional metal elements, such as at least two, at least three, at least four, or more, transitional metal elements.
The presently described alloy or alloy “sample” or “specimen” alloy can have any shape or size. For example, the alloy can have a shape of a particulate, which can have a shape such as spherical, ellipsoid, wire-like, rod-like, sheet-like, flake-like, or an irregular shape. The particulate can have any size. For example, it can have an average diameter of between about 1 micron and about 100 microns, such as between about 5 microns and about 80 microns, such as between about 10 microns and about 60 microns, such as between about 15 microns and about 50 microns, such as between about 15 microns and about 45 microns, such as between about 20 microns and about 40 microns, such as between about 25 microns and about 35 microns. For example, in one embodiment, the average diameter of the particulate is between about 25 microns and about 44 microns. In some embodiments, smaller particulates, such as those in the nanometer range, or larger particulates, such as those bigger than 100 microns, can be used.
The alloy sample or specimen can also be of a much larger dimension. For example, it can be a bulk structural component, such as an ingot, housing/casing of an electronic device or even a portion of a structural component that has dimensions in the millimeter, centimeter, or meter range.

Solid Solution

The term “solid solution” refers to a solid form of a solution. The term “solution” refers to a mixture of two or more substances, which may be solids, liquids, gases, or a combination of these. The mixture can be homogeneous or heterogeneous. The term “mixture” is a composition of two or more substances that are combined with each other and are generally capable of being separated. Generally, the two or more substances are not chemically combined with each other.

Alloy

In some embodiments, the alloy composition described herein can be fully alloyed. In one embodiment, an “alloy” refers to a homogeneous mixture or solid solution of two or more metals, the atoms of one replacing or occupying interstitial positions between the atoms of the other; for example, brass is an alloy of zinc and copper. An alloy, in contrast to a composite, can refer to a partial or complete solid solution of one or more elements in a metal matrix, such as one or more compounds in a metallic matrix. The term alloy herein can refer to both a complete solid solution alloy that can give single solid phase microstructure and a partial solution that can give two or more phases. An alloy composition described herein can refer to one comprising an alloy or one comprising an alloy-containing composite.
Thus, a fully alloyed alloy can have a homogenous distribution of the constituents, be it a solid solution phase, a compound phase, or both. The term “fully alloyed” used herein can account for minor variations within the error tolerance. For example, it can refer to at least 90% alloyed, such as at least 95% alloyed, such as at least 99% alloyed, such as at least 99.5% alloyed, such as at least 99.9% alloyed. The percentage herein can refer to either volume percent or weight percentage, depending on the context. These percentages can be balanced by impurities, which can be in terms of composition or phases that are not a part of the alloy.

Amorphous or Non-Crystalline Solid

An “amorphous” or “non-crystalline solid” is a solid that lacks lattice periodicity, which is characteristic of a crystal. As used herein, an “amorphous solid” includes “glass” which is an amorphous solid that softens and transforms into a liquid-like state upon heating through the glass transition. Generally, amorphous materials lack the long-range order characteristic of a crystal, though they can possess some short-range order at the atomic length scale due to the nature of chemical bonding. The distinction between amorphous solids and crystalline solids can be made based on lattice periodicity as determined by structural characterization techniques such as x-ray diffraction and transmission electron microscopy.
The terms “order” and “disorder” designate the presence or absence of some symmetry or correlation in a many-particle system. The terms “long-range order” and “short-range order” distinguish order in materials based on length scales.
The strictest form of order in a solid is lattice periodicity: a certain pattern (the arrangement of atoms in a unit cell) is repeated again and again to form a translationally invariant tiling of space. This is the defining property of a crystal. Possible symmetries have been classified in 14 Bravais lattices and 230 space groups.
Lattice periodicity implies long-range order. If only one unit cell is known, then by virtue of the translational symmetry it is possible to accurately predict all atomic positions at arbitrary distances. The converse is generally true, except, for example, in quasi-crystals that have perfectly deterministic tilings but do not possess lattice periodicity.
Long-range order characterizes physical systems in which remote portions of the same sample exhibit correlated behavior. This can be expressed as a correlation function, namely the spin-spin correlation function:
In the above function, s is the spin quantum number and x is the distance function within the particular system. This function is equal to unity when x=x′ and decreases as the distance |x−x′| increases. Typically, it decays exponentially to zero at large distances, and the system is considered to be disordered. If, however, the correlation function decays to a constant value at large |x−x′|, then the system can be said to possess long-range order. If it decays to zero as a power of the distance, then it can be called quasi-long-range order. Note that what constitutes a large value of |x−x′| is relative.
A system can be said to present quenched disorder when some parameters defining its behavior are random variables that do not evolve with time (i.e., they are quenched or frozen)—e.g., spin glasses. It is opposite to annealed disorder, where the random variables are allowed to evolve themselves. Embodiments herein include systems comprising quenched disorder.
The alloy described herein can be crystalline, partially crystalline, amorphous, or substantially amorphous. For example, the alloy sample/specimen can include at least some crystallinity, with grains/crystals having sizes in the nanometer and/or micrometer ranges. Alternatively, the alloy can be substantially amorphous, such as fully amorphous. In one embodiment, the alloy composition is at least substantially not amorphous, such as being substantially crystalline, such as being entirely crystalline.
In one embodiment, the presence of a crystal or a plurality of crystals in an otherwise amorphous alloy can be construed as a “crystalline phase” therein. The degree of crystallinity (or “crystallinity” for short in some embodiments) of an alloy can refer to the amount of the crystalline phase present in the alloy. The degree can refer to, for example, a fraction of crystals present in the alloy. The fraction can refer to volume fraction or weight fraction, depending on the context. A measure of how “amorphous” an amorphous alloy is can be amorphicity. Amorphicity can be measured in terms of a degree of crystallinity. For example, in one embodiment, an alloy having a low degree of crystallinity can be said to have a high degree of amorphicity. In one embodiment, for example, an alloy having 60 vol % crystalline phase can have a 40 vol % amorphous phase.

Amorphous Alloy or Amorphous Metal

An “amorphous alloy” is an alloy having an amorphous content of more than 50% by volume, preferably more than 90% by volume of amorphous content, more preferably more than 95% by volume of amorphous content, and most preferably more than 99% to almost 100% by volume of amorphous content. Note that, as described above, an alloy high in amorphicity is equivalently low in degree of crystallinity. An “amorphous metal” is an amorphous metal material with a disordered atomic-scale structure. In contrast to most metals, which are crystalline and therefore have a highly ordered arrangement of atoms, amorphous alloys are non-crystalline. Materials in which such a disordered structure is produced directly from the liquid state during cooling are sometimes referred to as “glasses.” Accordingly, amorphous metals are commonly referred to as “metallic glasses” or “glassy metals.” In one embodiment, a bulk metallic glass (“BMG”) can refer to an alloy, of which the microstructure is at least partially amorphous. However, there are several ways besides extremely rapid cooling to produce amorphous metals, including physical vapor deposition, solid-state reaction, ion irradiation, melt spinning, and mechanical alloying. Amorphous alloys can be a single class of materials, regardless of how they are prepared.
Amorphous metals can be produced through a variety of quick-cooling methods. For instance, amorphous metals can be produced by sputtering molten metal onto a spinning metal disk. The rapid cooling, on the order of millions of degrees a second, can be too fast for crystals to form, and the material is thus “locked in” a glassy state. Also, amorphous metals/alloys can be produced with critical cooling rates low enough to allow formation of amorphous structures in thick layers—e.g., bulk metallic glasses.
The terms “bulk metallic glass” (“BMG”), bulk amorphous alloy (“BAA”), and bulk solidifying amorphous alloy are used interchangeably herein. They refer to amorphous alloys having the smallest dimension at least in the millimeter range. For example, the dimension can be at least about 0.5 mm, such as at least about 1 mm, such as at least about 2 mm, such as at least about 4 mm, such as at least about 5 mm, such as at least about 6 mm, such as at least about 8 mm, such as at least about 10 mm, such as at least about 12 mm. Depending on the geometry, the dimension can refer to the diameter, radius, thickness, width, length, etc. A BMG can also be a metallic glass having at least one dimension in the centimeter range, such as at least about 1.0 cm, such as at least about 2.0 cm, such as at least about 5.0 cm, such as at least about 10.0 cm. In some embodiments, a BMG can have at least one dimension at least in the meter range. A BMG can take any of the shapes or forms described above, as related to a metallic glass. Accordingly, a BMG described herein in some embodiments can be different from a thin film made by a conventional deposition technique in one important aspect—the former can be of a much larger dimension than the latter.
Amorphous metals can be an alloy rather than a pure metal. The alloys may contain atoms of significantly different sizes, leading to low free volume (and therefore having viscosity up to orders of magnitude higher than other metals and alloys) in a molten state. The viscosity prevents the atoms from moving enough to form an ordered lattice. The material structure may result in low shrinkage during cooling and resistance to plastic deformation. The absence of grain boundaries, the weak spots of crystalline materials in some cases, may, for example, lead to better resistance to wear and corrosion. In one embodiment, amorphous metals, while technically glasses, may also be much tougher and less brittle than oxide glasses and ceramics.
Thermal conductivity of amorphous materials may be lower than that of their crystalline counterparts. To achieve formation of an amorphous structure even during slower cooling, the alloy may be made of three or more components, leading to complex crystal units with higher potential energy and lower probability of formation. The formation of amorphous alloy can depend on several factors: the composition of the components of the alloy; the atomic radius of the components (preferably with a significant difference of over 12% to achieve high packing density and low free volume); and the negative heat of mixing the combination of components, inhibiting crystal nucleation and prolonging the time the molten metal stays in a supercooled state. However, as the formation of an amorphous alloy is based on many different variables, it can be difficult to make a prior determination of whether an alloy composition would form an amorphous alloy.
Amorphous alloys, for example, of boron, silicon, phosphorus, and other glass formers with magnetic metals (iron, cobalt, nickel) may be magnetic, with low coercivity and high electrical resistance. The high resistance leads to low losses by eddy currents when subjected to alternating magnetic fields, a property useful, for example, as transformer magnetic cores.
Amorphous alloys may have a variety of potentially useful properties. In particular, they tend to be stronger than crystalline alloys of similar chemical composition, and they can sustain larger reversible (“elastic”) deformations than crystalline alloys. Amorphous metals derive their strength directly from their non-crystalline structure, which can have none of the defects (such as dislocations) that limit the strength of crystalline alloys. For example, one modem amorphous metal, known as Vitreloy™, has a tensile strength that is almost twice that of high-grade titanium. In some embodiments, metallic glasses at room temperature are not ductile and tend to fail suddenly when loaded in tension, which limits the material applicability in reliability-critical applications, as the impending failure is not evident. Therefore, to overcome this challenge, metal matrix composite materials having a metallic glass matrix containing dendritic particles or fibers of a ductile crystalline metal can be used. Alternatively, a BMG low in element(s) that tend to cause embitterment (e.g., Ni) can be used. For example, a Ni-free BMG can be used to improve the ductility of the BMG.
Another useful property of bulk amorphous alloys is that they can be true glasses; in other words, they can soften and flow upon heating. This can allow for easy processing, such as by injection molding, in much the same way as polymers. As a result, amorphous alloys can be used for making sports equipment, medical devices, electronic components and equipment, and thin films. Thin films of amorphous metals can be deposited as protective coatings via a high velocity oxygen fuel technique.
A material can have an amorphous phase, a crystalline phase, or both. The amorphous and crystalline phases can have the same chemical composition and differ only in the microstructure—i.e., one amorphous and the other crystalline. Microstructure in one embodiment refers to the structure of a material as revealed by a microscope at 25× magnification or higher. Alternatively, the two phases can have different chemical compositions and microstructures. For example, a composition can be partially amorphous, substantially amorphous, or completely amorphous.
As described above, the degree of amorphicity (and conversely the degree of crystallinity) can be measured by fraction of crystals present in the alloy. The degree can refer to volume fraction of weight fraction of the crystalline phase present in the alloy. A partially amorphous composition can refer to a composition of at least about 5 vol % of which is of an amorphous phase, such as at least about 10 vol %, such as at least about 20 vol %, such as at least about 40 vol %, such as at least about 60 vol %, such as at least about 80 vol %, such as at least about 90 vol %. The terms “substantially” and “about” have been defined elsewhere in this application. Accordingly, a composition that is at least substantially amorphous can refer to one of which at least about 90 vol % is amorphous, such as at least about 95 vol %, such as at least about 98 vol %, such as at least about 99 vol %, such as at least about 99.5 vol %, such as at least about 99.8 vol %, such as at least about 99.9 vol %. In one embodiment, a substantially amorphous composition can have some incidental, insignificant amount of crystalline phase present therein.
In one embodiment, an amorphous alloy composition can be homogeneous with respect to the amorphous phase. A substance that is uniform in composition is homogeneous. This is in contrast to a substance that is heterogeneous. The term “composition” refers to the chemical composition and/or microstructure in the substance. A substance is homogeneous when a volume of the substance is divided in half and both halves have substantially the same composition. For example, a particulate suspension is homogeneous when a volume of the particulate suspension is divided in half and both halves have substantially the same volume of particles. However, it might be possible to see the individual particles under a microscope. Another example of a homogeneous substance is air where different ingredients therein are equally suspended, though the particles, gases and liquids in air can be analyzed separately or separated from air.
A composition that is homogeneous with respect to an amorphous alloy can refer to one having an amorphous phase substantially uniformly distributed throughout its microstructure. In other words, the composition macroscopically comprises a substantially uniformly distributed amorphous alloy throughout the composition. In an alternative embodiment, the composition can be of a composite, having an amorphous phase having therein a non-amorphous phase. The non-amorphous phase can be a crystal or a plurality of crystals. The crystals can be in the form of particulates of any shape, such as spherical, ellipsoid, wire-like, rod-like, sheet-like, flake-like, or an irregular shape. In one embodiment, it can have a dendritic form. For example, an at least partially amorphous composite composition can have a crystalline phase in the shape of dendrites dispersed in an amorphous phase matrix; the dispersion can be uniform or non-uniform, and the amorphous phase and the crystalline phase can have the same or a different chemical composition. In one embodiment, they have substantially the same chemical composition. In another embodiment, the crystalline phase can be more ductile than the BMG phase.
The methods described herein can be applicable to any type of amorphous alloy. Similarly, the amorphous alloy described herein as a constituent of a composition or article can be of any type. The amorphous alloy can comprise the element Zr, Hf, Ti, Cu, Ni, Pt, Pd, Fe, Mg, Au, La, Ag, Al, Mo, Nb, Be, or combinations thereof. Namely, the alloy can include any combination of these elements in its chemical formula or chemical composition. The elements can be present at different weight or volume percentages. For example, an iron “based” alloy can refer to an alloy having a non-insignificant weight percentage of iron present therein, the weight percent can be, for example, at least about 20 wt %, such as at least about 40 wt %, such as at least about 50 wt %, such as at least about 60 wt %, such as at least about 80 wt %. Alternatively, in one embodiment, the above-described percentages can be volume percentages, instead of weight percentages. Accordingly, an amorphous alloy can be zirconium-based, titanium-based, platinum-based, palladium-based, gold-based, silver-based, copper-based, iron-based, nickel-based, aluminum-based, molybdenum-based, and the like. The alloy can also be free of any of the aforementioned elements to suit a particular purpose. For example, in some embodiments, the alloy, or the composition including the alloy, can be substantially free of nickel, aluminum, titanium, beryllium, or combinations thereof. In one embodiment, the alloy or the composite is completely free of nickel, aluminum, titanium, beryllium, or combinations thereof.
For example, the amorphous alloy can have the formula (Zr, Ti)a(Ni, Cu, Fe)b(Be, Al, Si, B)c, wherein a, b, and c each represents a weight or atomic percentage. In one embodiment, a is in the range of from 30 to 75, b is in the range of from 5 to 60, and c is in the range of from 0 to 50 in atomic percentages. Alternatively, the amorphous alloy can have the formula (Zr, Ti)a(Ni, Cu)b(Be)c, wherein a, b, and c each represents a weight or atomic percentage. In one embodiment, a is in the range of from 40 to 75, b is in the range of from 5 to 50, and c is in the range of from 5 to 50 in atomic percentages. The alloy can also have the formula (Zr, Ti)a(Ni, Cu)b(Be)c, wherein a, b, and c each represents a weight or atomic percentage. In one embodiment, a is in the range of from 45 to 65, b is in the range of from 7.5 to 35, and c is in the range of from 10 to 37.5 in atomic percentages. Alternatively, the alloy can have the formula (Zr)a(Nb, Ti)b(Ni, Cu)c(Al)d, wherein a, b, c, and d each represents a weight or atomic percentage. In one embodiment, a is in the range of from 45 to 65, b is in the range of from 0 to 10, c is in the range of from 20 to 40 and d is in the range of from 7.5 to 15 in atomic percentages. One exemplary embodiment of the aforedescribed alloy system is a Zr—Ti—Ni—Cu—Be based amorphous alloy under the trade name Vitreloy™, such as Vitreloy-1 and Vitreloy-101, as fabricated by Liquidmetal Technologies, CA, USA. Some examples of amorphous alloys of the different systems are provided in Table 1 and Table 2.

TABLE 1

Exemplary amorphous alloy compositions

Alloy	Atm %	Atm %	Atm %	Atm %	Atm %	Atm %	Atm %	Atm %

1	Fe	Mo	Ni	Cr	P	C	B
	68.00%	5.00%	5.00%	2.00%	12.50%	5.00%	2.50%
2	Fe	Mo	Ni	Cr	P	C	B	Si
	68.00%	5.00%	5.00%	2.00%	11.00%	5.00%	2.50%	1.50%
3	Pd	Cu	Co	P
	44.48%	32.35%	4.05%	19.11%
4	Pd	Ag	Si	P
	77.50%	6.00%	9.00%	7.50%
5	Pd	Ag	Si	P	Ge
	79.00%	3.50%	9.50%	6.00%	2.00%
5	Pt	Cu	Ag	P	B	Si
	74.70%	1.50%	0.30%	18.0%	4.00%	1.50%

TABLE 2

Additional Exemplary amorphous alloy compositions (atomic %)

Alloy	Atm %	Atm %	Atm %	Atm %	Atm %	Atm %

1	Zr	Ti	Cu	Ni	Be
	41.20%	13.80%	12.50%	10.00%	22.50%
2	Zr	Ti	Cu	Ni	Be
	44.00%	11.00%	10.00%	10.00%	25.00%
3	Zr	Ti	Cu	Ni	Nb	Be
	56.25%	11.25%	6.88%	5.63%	7.50%	12.50%
4	Zr	Ti	Cu	Ni	Al	Be
	64.75%	5.60%	14.90%	11.15%	2.60%	1.00%
5	Zr	Ti	Cu	Ni	Al
	52.50%	5.00%	17.90%	14.60%	10.00%
6	Zr	Nb	Cu	Ni	Al
	57.00%	5.00%	15.40%	12.60%	10.00%
7	Zr	Cu	Ni	Al
	50.75%	36.23%	4.03%	9.00%
8	Zr	Ti	Cu	Ni	Be
	46.75%	8.25%	7.50%	10.00%	27.50%
9	Zr	Ti	Ni	Be
	21.67%	43.33%	7.50%	27.50%
10	Zr	Ti	Cu	Be
	35.00%	30.00%	7.50%	27.50%
11	Zr	Ti	Co	Be
	35.00%	30.00%	6.00%	29.00%
12	Zr	Ti	Fe	Be
	35.00%	30.00%	2.00%	33.00%
13	Au	Ag	Pd	Cu	Si
	49.00%	5.50%	2.30%	26.90%	16.30%
14	Au	Ag	Pd	Cu	Si
	50.90%	3.00%	2.30%	27.80%	16.00%
15	Pt	Cu	Ni	P
	57.50%	14.70%	5.30%	22.50%
16	Zr	Ti	Nb	Cu	Be
	36.60%	31.40%	7.00%	5.90%	19.10%
17	Zr	Ti	Nb	Cu	Be
	38.30%	32.90%	7.30%	6.20%	15.30%
18	Zr	Ti	Nb	Cu	Be
	39.60%	33.90%	7.60%	6.40%	12.50%
19	Cu	Ti	Zr	Ni
	47.00%	34.00%	11.00%	8.00%
20	Zr	Co	Al
	55.00%	25.00%	20.00%

Other exemplary ferrous metal-based alloys include compositions such as those disclosed in U.S. Patent Application Publication Nos. 2007/0079907 and 2008/0118387. These compositions include the Fe(Mn, Co, Ni, Cu) (C, Si, B, P, Al) system, wherein the Fe content is from 60 to 75 atomic percentage, the total of (Mn, Co, Ni, Cu) is in the range of from 5 to 25 atomic percentage, and the total of (C, Si, B, P, Al) is in the range of from 8 to 20 atomic percentage, as well as the exemplary composition Fe48Cr15Mo14Y2C15B6. They also include the alloy systems described by Fe—Cr—Mo—(Y,Ln)—C—B, Co—Cr—Mo-Ln-C—B, Fe—Mn—Cr—Mo—(Y,Ln)—C—B, (Fe, Cr, Co)—(Mo,Mn)—(C,B)—Y, Fe—(Co,Ni)—(Zr,Nb,Ta)—(Mo,W)—B, Fe—(Al,Ga)—(P,C,B,Si,Ge), Fe—(Co, Cr,Mo,Ga,Sb)—P—B—C, (Fe, Co)—B—Si—Nb alloys, and Fe—(Cr—Mo)—(C,B)—Tm, where Ln denotes a lanthanide element and Tm denotes a transition metal element. Furthermore, the amorphous alloy can also be one of the exemplary compositions Fe80P12.5C5B2.5, Fe80P11C5B2.5Si1.5, Fe74.5Mo5.5P12.5C5B2.5, Fe74.5Mo5.5P11C5B2.5Si1.5, Fe70Mo5Ni5P12.5C5B2.5, Fe70Mo5Ni5P11C5B2.5Si1.5, Fe68Mo5Ni5Cr2P12.5C5B2.5, and Fe68Mo5Ni5Cr2P11C5B2.5Si1.5, described in U.S. Patent Application Publication No. 2010/0300148.
The amorphous alloys can also be ferrous alloys, such as (Fe, Ni, Co) based alloys. Examples of such compositions are disclosed in U.S. Pat. Nos. 6,325,868; 5,288,344; 5,368,659; 5,618,359; and 5,735,975, Inoue et al., Appl. Phys. Lett., Volume 71, p 464 (1997), Shen et al., Mater. Trans., JIM, Volume 42, p 2136 (2001), and Japanese Patent Application No. 200126277 (Pub. No. 2001303218 A). One exemplary composition is Fe72Al5Ga2P11C6B4. Another example is Fe72Al7Zr10Mo5W2B15. Another iron-based alloy system that can be used in the coating herein is disclosed in U.S. Patent Application Publication No. 2010/0084052, wherein the amorphous metal contains, for example, manganese (1 to 3 atomic %), yttrium (0.1 to 10 atomic %), and silicon (0.3 to 3.1 atomic %) in the range of composition given in parentheses; and that contains the following elements in the specified range of composition given in parentheses: chromium (15 to 20 atomic %), molybdenum (2 to 15 atomic %), tungsten (1 to 3 atomic %), boron (5 to 16 atomic %), carbon (3 to 16 atomic %), and the balance iron.
The aforedescribed amorphous alloy systems can further include additional elements, such as additional transition metal elements, including Nb, Cr, V, and Co. The additional elements can be present at less than or equal to about 30 wt %, such as less than or equal to about 20 wt %, such as less than or equal to about 10 wt %, such as less than or equal to about 5 wt %. In one embodiment, the additional, optional element is at least one of cobalt, manganese, zirconium, tantalum, niobium, tungsten, yttrium, titanium, vanadium and hafnium to form carbides and further improve wear and corrosion resistance. Further optional elements may include phosphorous, germanium and arsenic, totaling up to about 2%, and preferably less than 1%, to reduce melting point. Otherwise incidental impurities should be less than about 2% and preferably 0.5%.
In some embodiments, a composition having an amorphous alloy can include a small amount of impurities. The impurity elements can be intentionally added to modify the properties of the composition, such as improving the mechanical properties (e.g., hardness, strength, fracture mechanism, etc.) and/or improving the corrosion resistance. Alternatively, the impurities can be present as inevitable, incidental impurities, such as those obtained as a byproduct of processing and manufacturing. The impurities can be less than or equal to about 10 wt %, such as about 5 wt %, such as about 2 wt %, such as about 1 wt %, such as about 0.5 wt %, such as about 0.1 wt %. In some embodiments, these percentages can be volume percentages instead of weight percentages. In one embodiment, the alloy sample/composition consists essentially of the amorphous alloy (with only a small incidental amount of impurities). In another embodiment, the composition includes the amorphous alloy (with no observable trace of impurities).

Electronic Devices

The embodiments herein can be valuable in the fabrication of electronic devices using a BMG. An electronic device herein can refer to any electronic device known in the art. For example, it can be a telephone, such as a cell phone, and a land-line phone, or any communication device, such as a smart phone, including, for example an iPhone™, and an electronic email sending/receiving device. It can be a part of a display, such as a digital display, a TV monitor, an electronic-book reader, a portable web-browser (e.g., iPad™), and a computer monitor. It can also be an entertainment device, including a portable DVD player, conventional DVD player, Blue-Ray disk player, video game console, music player, such as a portable music player (e.g., iPod™), etc. It can also be a part of a device that provides control, such as controlling the streaming of images, videos, sounds (e.g., Apple TV™), or it can be a remote control for an electronic device. It can be a part of a computer or its accessories, such as the hard drive tower housing or casing, laptop housing, laptop keyboard, laptop track pad, desktop keyboard, mouse, and speaker. The article can also be applied to a device such as a watch or a clock.

Embodiments

Provided in one embodiment is a method of coating a substrate with a bulk-solidifying amorphous alloy using a flame spraying method in which the substrate has a thickness greater than the critical casting thickness of the bulk-solidifying amorphous alloy. One embodiment provides a method of coating a substrate with a bulk-solidifying amorphous alloy that includes thermal spraying a bulk-solidifying amorphous alloy on at least one surface of a substrate having a thickness greater than the critical casting thickness of the bulk-solidifying amorphous alloy, and at a temperature cool enough that the sprayed alloy cools fast enough to avoid crystallization, thereby providing a substrate coated with the bulk-solidifying amorphous alloy in substantially amorphous form.
Provided in another embodiment is a method of coating a substrate with a bulk-solidifying amorphous alloy using a flame spraying method in which the substrate has a thickness greater than the critical casting thickness of the bulk-solidifying amorphous alloy. In accordance with one embodiment, there is provided a method of coating a substrate with a bulk-solidifying amorphous alloy that includes providing a powder alloy composition of a bulk-solidifying amorphous alloy to a thermal spray apparatus, thermally spraying a relatively uniform coating of the bulk-solidifying amorphous alloy onto at least a surface of the substrate such that the coating layer cools sufficiently rapidly to maintain the amorphous characteristic of the bulk-solidifying amorphous alloy, thereby providing a substrate coated with a substantially amorphous bulk-solidifying amorphous alloy.
Provided in another embodiment is a method of coating a substrate with a bulk-solidifying amorphous alloy that includes depositing a brazing layer on the substrate, optionally heating the substrate to fuse the brazing layer to the substrate and subsequently cooling the substrate and brazing later, thermal spraying a bulk-solidifying amorphous alloy on at least one surface of a substrate having a thickness greater than the critical casting thickness of the bulk-solidifying amorphous alloy to provide a substrate coated with a substantially amorphous bulk-solidifying amorphous alloy.
The embodiments provide a substrate coated with a bulk-solidifying amorphous alloy in such a manner that the alloy is substantially amorphous after coating. In embodiment, the alloy is at least 95% amorphous, or at least 98% amorphous, or at least 99% amorphous. Bulk-solidifying amorphous alloys could be formed into a thin sheet by sputtering on a spinning disk, or by using other methods described above. This sheet then can be positioned on a substrate and then joined via heating to maintain the amorphous characteristics of the alloy. This method is time consuming, expensive, and cannot readily be used on intricately-shaped articles. Casting an amorphous alloy layer also has its limitations. Thermal spraying a coating layer provides the advantages of coating very thin layers on intricately-shaped substrates, but can result in losing the amorphous characteristics of the coated alloy if the alloy is not cooled properly on the substrate, or can result in an inadequate bond if cooled too rapidly.
The present inventors surprisingly found that the amorphous characteristics of the bulk-solidifying amorphous alloy can be maintained by providing a substrate of sufficient thickness to serve as a heat sink and permit rapid enough cooling. A suitable thickness for the substrate is a thickness greater than the critical casting thickness of the bulk-solidifying amorphous alloy. Typical critical casting thicknesses for bulk-solidifying amorphous alloys are from about 1 to about 100 mm, or from about 3 to about 50 mm, or from about 8 to about 30 mm. The inventors also have found that cooling the substrate prior to coating also can maintain the amorphous characteristics of the bulk-solidifying amorphous alloy, even if the substrate is thinner than the critical casting thickness. A substrate that is too cool, however, could result in the formation of a coating that is not properly adhered to the surface of the substrate because it is advantageous that some interdiffusion bonding occur at the interface between the substrate and the bulk-solidifying amorphous alloy. The inventors also have found that use of a brazing layer may also serve as an additional heat sink to provide the requisite cooling, while at the same time provide a more secure bond with the underlying substrate.

Coating

The term “coating” refers to a covering, e.g., a layer of material, which is applied to the surface of an object, usually referred to as the “substrate.” In one embodiment, at least one of the presently described compositions, including those comprising the aforedescribed alloy powder compositions, is applied onto a substrate to form a coating. In one embodiment, the coating consists essentially of the bulk-solidifying amorphous alloy. The substrate can be of any type of suitable substrate, such as a metal substrate, a ceramic substrate, or a combination thereof. Because of the properties of the bulk-solidifying amorphous alloy composition, a coating made therefrom can have superior properties.
For example, the coating can have high hardness. In one embodiment, the coating can have a Vickers hardness of at least about 800 HV-100 gm, such as at least about 850 HV-100 gm, such as at least about 1000 HV-100 gm, such as at least about 1100 HV-100 gm, such as at least about 1200 HV-100 gm, such as at least about 1250 HV-100 gm, such as at least about 1300 HV-100 gm. In one embodiment, the coating comprising the amorphous alloy can have a yield strength of about 200 ksi or higher, such as 250 ksi or higher, such as 400 ksi or higher, such as 500 ksi or higher, such as 600 ksi or higher. In another embodiment, the coating comprising the amorphous alloy can have a very high elastic strain limit, such as at least about 1.2%, such as at least about 1.5%, such as at least about 1.6%, such as at least about 1.8%, such as at least about 2.0%. Amorphous alloys also may exhibit high strength-to weight ratios, particularly in the case of, for example, Ti-based and Fe-based alloys. They also can have high resistance to corrosion and high environmental durability, particularly, for example, the Zr-based and Ti-based alloys. The embodiments enable the manufacture of materials without requiring the underlying substrate to have the requisite hardness, yield strength, elastic strain limit, strength-to-weight ratio, etc., thus providing a more cost-efficient method of making ultra-hard materials having these desirable properties. In addition, the surface can have the hardness described herein, whereas the underlying substrate may have a much greater degree of deformability.
The coating can be wear-resistant and/or corrosion resistant. Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. This can refer to the electrochemical oxidation of metals in reaction with an oxidant such as oxygen. Formation of an oxide of a metal due to oxidation of the metal atoms in a solid solution is an example of electrochemical corrosion termed rusting. This type of damage typically can produce oxide(s) and/or salt(s) of the original metal. Corrosion can also refer to materials other than metals, such as ceramics or polymers, although in this context, the term degradation is more common. In other words, corrosion is the wearing away of metals due to a chemical reaction.
Metals and alloys could corrode merely from exposure to moisture in the air, but the process can be strongly affected by exposure to certain substances such as salts. Corrosion can be concentrated locally to form a pit or crack, or it can extend across a wide area more or less uniformly corroding the surface. Because corrosion is a diffusion controlled process, it can occur on exposed surfaces. As a result, methods to reduce the activity of the exposed surface, such as a coating, passivation and chromate-conversion, can increase a material's corrosion resistance.
The term “corrosion resistant” in the context of the coatings of the embodiments herein can refer to a material having a coating that has substantially less corrosion when exposed to an environment than that of the same material without the coating that is exposed to the same environment. In one embodiment, the coating described herein provides improved corrosion resistance relative to a coating that does not meet the specifications of the presently described coating, with respect to chemical composition and the amorphous nature of the material. In one embodiment, the additional processing of the coating, which may include heating and subsequent cooling, provides a coating having superior corrosion resistance, with respect to coatings that have not been further processed in accordance with the preferred embodiments described herein.
The coating preferably can exhibit desirable hardness, toughness, and bonding characteristics. The coating also can be fully dense and suitable for very wide temperature ranges. The coating in one embodiment is substantially amorphous or fully amorphous. For example, the coating can have at least 90% of its volume being amorphous, such as at least 95%, such as at least 98%, such as at least 99%, being amorphous.
One unexpected desirable property of one the preferred alloy composition that is the increase in the thermal conductivity of the presently described alloy composition. The thermal conductivity of the presently described bulk-solidifying amorphous alloy can be at least 2 W/mk, such as at least 3 W/mk, such as at least 5 W/mk, such as at least 10 W/mk. In one embodiment, the preferred compositions have a thermal conductivity of between about 1 W/mk and about 10 W/mk, such as about 2 W/mk and about 6 W/mk, such as about 3 W/mk and about 5 W/mk, such as about 3.5 W/mk and about 4 W/mk.
Also, not to be bound by any particular theory, but the increase in the thermal conductivity can result in an accelerated cooling of the alloy. One result of such expedited cooling can be an increase in amorphous phase of the alloy. This can be particularly beneficial when the resulting material is intended for use in which a harder, more corrosion resistant surface is desirable.
The coating produced by the methods and compositions described herein can be dense. For example, it can have less than or equal to about 10% (volume) of porosity, such as less than or equal to about 5% of porosity, such as less than or equal to about 2% of porosity, such as less than or equal to about 1% of porosity, such as less than or equal to about 0.5% of porosity. Depending on the context, including the materials and the production and processing methods used, the aforedescribed percentages can be weight percentages, instead of volume percentages. It is particularly preferred that after the heating and cooling, the coating have significantly less than 0.5% porosity and be substantially smooth.
The thickness of the coating can be from about 0.001″ to about 0.1″, such as about 0.005″ to about 0.08″, and such as from about 0.020″ to about 0.050″, such as from about 0.015″ to about 0.03″, such as from about 0.02″ to about 0.025″. In one embodiment wherein the coating is fabricated by arc spraying, the coating can have a thickness of about 0.02″ to about 0.03″. In an alternative embodiment wherein the coating is fabricated by HVOF, the coating may have a thickness of about 0.015″ to about 0.03″.
The coating can include any of the bulk-solidifying amorphous alloy powder composition as described above. In addition to the alloy powder composition, the coating can include additional elements or materials, such as those from a binder. The term “binder” refers to a material used to bind other materials. The coating can also include any additives intentionally added or incidental impurities. In one embodiment, the coating consists essentially of the alloy powder composition, such as consisting of the alloy powder compositions described above.
There are several advantages of the coatings of the embodiments herein. For example, the coating will retain its integrity without separating from the surface of the substrate. In addition, it can withstand high temperature, and could be more ductile and fatigue resistant than conventional coatings.
When the alloy powder composition is used to fabricate a product, such as a coating, additional materials can be optionally added. For example, in one embodiment wherein the alloyed powder is used to fabricate a coating on a substrate, some optional elements can be added in a small amount, such as less than 15 wt %, such as less than 10 wt %, such as less than 5 wt %. These elements can include, for example, cobalt, molybdenum, manganese, zirconium, tantalum, niobium, tungsten, yttrium, titanium, vanadium, hafnium, or combinations thereof. These elements, alone or in combination, can form compounds, such as carbides, to further improve wear and corrosion resistance.
Some other optional elements can be added to modify other properties of the fabricated coating. For example, elements such as phosphorous, germanium, arsenic, or combinations thereof, can be added to reduce the melting point of the composition. These elements can be added in a small amount, such as less than 10 wt %, such as less than 5 wt %, such as less than 2 wt %, such as less than 1 wt %, such as less than 0.5 wt %.

Coating Method

In one embodiment, the method of forming such a coating can include disposing a coating onto a substrate. The substrate can be of any type. The substrate can be, for example, a metal substrate, such as a steel substrate. In one embodiment, the substrate is thick enough to function as a heat sink to provide effective cooling of the coating, but not so rapidly that the coating does not adequately adhere to the surface of the substrate. In one embodiment, the sprayed alloy coating can become a part of a hard-facing structure/material. The coating can comprise any of the compositions provided herein. For example, it can have a microstructure that is at least substantially amorphous, such as completely amorphous. In one embodiment, the alloy composition can be formed in-situ.
In one embodiment, the method can further include steps of making or providing the alloy powder composition. The composition can be any of the compositions provided herein. Various techniques can be used to fabricate the alloy powder composition. One such technique is atomization.
Atomization is one way of combining the coatings of the embodiments herein. One example of atomization can be gas atomization, which can refer to a method in which molten metal is broken up into smaller particles by a rapidly moving inert gas stream. The gas stream can include non-reactive gas(s), such as inert gases including argon or nitrogen. While the various constituents can be physically mixed or blended together before coating, in some embodiments, atomization, such as a gas atomization, is preferred.
In one embodiment, the method of coating or making a coating, can include providing a mixture; forming the mixture into a powder composition; and subsequently disposing the powder composition onto a substrate to form the coating. The composition can be any of the aforedescribed compositions. The mixture of the various elements, including zirconium, titanium, copper, beryllium, nickel, niobium, aluminum, gold, silver, palladium, silicon, cobalt, and the like, can be pre-mixed, or they can be mixed in an additional step. The elements in the mixture can include any of the elements of the alloy powder composition. In one embodiment wherein the alloy composition produced is one that comprises zirconium, titanium, copper, nickel, and beryllium in their elemental form, alloy form, composite form, compound form, or a combination thereof. The mixture is substantially free of an amorphous phase or can contain some amorphous phase.
Forming the coating can be carried out by atomization, as described above. The alloy powder composition can then be disposed onto a substrate. The inventors have found that superior coatings can be achieved by use of a thermal spraying (or flame spraying) technique. Suitable thermal spraying techniques include, for example, flame spraying, high-velocity oxy-fuel coating spraying (HVOF), plasma spraying, or combinations thereof. The thermal spray can be carried out in one or more steps of operation. Certain preferred coatings techniques will be described below in more detail with reference to FIGS. 3 and 4.
The presently described HVOF coatings can be dense with very low porosity (as aforedescribed) and/or little oxide inclusions and could be finished to low single digit room mean square (“Ra”) values, which is an indicator of the smoothness of the layer. The plasma flame sprayed coatings in accordance with the embodiments also may be dense, low in oxide stringers, and show good alloying of the cored wire.
When used for thermal spraying, such as HVOF, the alloy thermal spray material preferably is fully alloyed. However, it need not be in an amorphous form, and even may have the ordinary macro-crystalline structure resulting from the normal cooling rates in the usual production procedures. Thus, the thermal spray powder may be made by such a standard method as atomizing from the melt and cooling the droplets under ambient conditions. The thermal spraying then melts the particles that quench on a surface being coated, providing a coating that may be substantially or entirely amorphous. By using the usual manufacturing procedures, the production of the thermal spray powder is kept relatively simple and costs are minimized.
Thermal spraying can refer to a coating process in which melted (or heated) materials are sprayed onto a surface. The “feedstock” (coating precursor) can be heated by, for example, electrical (plasma or arc) or chemical means (combustion flame). Thermal spraying can provide thick coatings (e.g., thickness range of about 20 micrometers or more, such as to the millimeter range) over a large area at a high deposition rate, as compared to other coating processes. Thermal spraying also can provide coatings on intricately shaped articles. The feedstock can be fed into the system in powder or wire form, heated to a molten or semi-molten state, and then accelerated towards substrates in the form of micrometer-size particles. Combustion or electrical arc discharge can be used as the source of energy for thermal spraying. Resulting coatings can be made by the accumulation of numerous sprayed particles. Because the surface may not heat up significantly, thermal spray coating can have an advantage of allowing the coating of flammable substances.
The composition can include any of the aforementioned alloy powder compositions. Thermal spraying is generally referred to as a process that uses heat to deposit molten or semi-molten materials onto a substrate to protect the substrate from wear and corrosion. In a thermal spraying process the material to be deposited is supplied in a powder form, for example. Such powders could comprise small particles, e.g., between 100-mesh U.S. Standard screen size (149 microns) and about 2 microns.
The presently described alloy powder compositions can be used in a number of (fully or substantially fully) alloyed forms, such as cast, sintered, or welded forms, or as a quenched powder or ribbon. The composition can be especially suitable for application as a coating produced by thermal spraying. Any type of thermal spraying, such as plasma, flame, arc-plasma, are and combustion, and High Velocity Oxy-Fuel (HVOF) spraying, can be used. In one embodiment, a high velocity thermal spraying process, such as HVOF, is used.
An embodiment of the HVOF process is shown in FIG. 3. The HVOF thermal spray process is substantially the same as the combustion powder spray process (“LVOF”) except that this process has been developed to produce extremely high spray velocity. There are a number of HVOF guns that use different methods to achieve high velocity spraying. One method is basically a high pressure water cooled combustion chamber and a long nozzle. Fuel (kerosene, acetylene, propylene and hydrogen) and oxygen are fed into the chamber, combustion produces a hot high pressure flame that is forced down a nozzle increasing its velocity. Powder may be fed axially into the combustion chamber under high pressure or fed through the side of a laval type nozzle where the pressure is lower. Another method uses a simpler system of a high pressure combustion nozzle and air cap. Fuel gas (propane, propylene or hydrogen) and oxygen are supplied at high pressure, and combustion occurs outside the nozzle but within an air cap supplied with compressed air. The compressed air pinches and accelerates the flame and acts as a coolant for the gun. Powder is fed at high pressure axially from the center of the nozzle.
In HVOF, a mixture of gaseous or liquid fuel and oxygen is fed into a combustion chamber, where they are ignited and combusted continuously. The resultant hot gas at a pressure close to 1 MPa emanates through a converging—diverging nozzle and travels through a straight section. The fuels can be gases (hydrogen, methane, propane, propylene, acetylene, natural gas, etc.) or liquids (kerosene, etc.). The jet velocity at the exit of the barrel (>1000 m/s) exceeds the speed of sound. A powder feed stock is injected into the gas stream, which accelerates the powder up to 800 m/s. The stream of hot gas and powder is directed towards the surface to be coated. The powder partially melts in the stream, and deposits upon the substrate. The resulting coating has low porosity and high bond strength.
HVOF coatings may be as thick as 12 mm (½″). It is typically used to deposit wear and corrosion resistant coatings on materials, such as ceramic and metallic layers.
Another method of making the coatings of the embodiments herein can be by a plasma thermal spray process shown in FIG. 4. The plasma spray process substantially involves spraying molten or heat softened material onto a surface to provide a coating. Material in the form of powder is injected into a very high temperature plasma flame, where it is rapidly heated and accelerated to a high velocity. The hot material impacts on the substrate surface and rapidly cools forming a coating. This process carried out correctly is called a “cold process” (relative to the substrate material being coated) as the substrate temperature can be kept low during processing to avoid damage, metallurgical changes and distortion to the substrate material.
The plasma gun comprises a copper anode and tungsten cathode, both of which are water cooled. Plasma gas (argon, nitrogen, hydrogen, helium) flows around the cathode and through the anode which is shaped as a constricting nozzle. The plasma is initiated by a, high voltage discharge which causes localized ionization and a conductive path for a DC arc to form between the cathode and anode. The resistance heating from the arc causes the gas to reach extreme temperatures, dissociate, and ionize to form a plasma. The plasma exits the anode nozzle as a free or neutral plasma flame (plasma which does not carry an electric current) which is quite different from the plasma transferred arc coating process where the arc extends to the surface to be coated. When the plasma is stabilized and ready for spraying the electric arc extends down the nozzle, instead of shorting out to the nearest edge of the anode nozzle. This stretching of the arc is due to a thermal pinch effect. Cold gas around the surface of the water cooled anode nozzle being electrically non-conductive constricts the plasma arc, raising its temperature and velocity. Powder is fed into the plasma flame most commonly via an external powder port mounted near the anode nozzle exit. The powder is so rapidly heated and accelerated that spray distances can be in the order of 25 to 150 mm.
In one embodiment wherein the composition is used as a thermal spray material, the composition is desirably in an alloy form (as opposed to a composite of the constituents). Not to be bound to any particular theory, but desirable effects can be obtained during thermal flame spraying when the homogeneity of the sprayed composition is maximized—i.e., as an alloy, as opposed to a composite. In fact, alloyed powder of size and flowability suitable for thermal spraying can provide such a venue of homogeneity maximization. The powder particle can take any shape, such as spherical particles, elliptical particles, irregular shaped particles, or flakes, such as flat flakes. In one embodiment, the alloyed powder can have a particle size that falls in a range between 100-mesh (U.S. standard screen size—i.e., 149 microns) and about 2 microns. Furthermore, the thermal spray material may be used as is or, for example, as a powder blended with at least one other thermal spray powder, such as tungsten carbide.
In some embodiments, the presently described powder-containing alloy composition used as a part of thermal spray material can be fully alloyed, or at least substantially alloyed. Thus, the process can further include a step of pre-alloying and processing at least some of the alloy powder composition into a powder form prior to the step of disposing. The alloy powder composition need not be in an amorphous form. The composition, for example, can have at least some crystallinity, such as being fully crystalline, or can be at least partially amorphous, such as substantially amorphous or fully amorphous. Not to be bound by any particular theory, but some of crystallinity can arise from the normal cooling rates in the pre-existing alloyed powder production procedures. In other words, the thermal spray powder may be made by such standard methods as atomizing from the melt and cooling the droplets under ambient conditions, such as in air. In one embodiment, the alloyed powder can be manufactured by a method, such as atomization using non-reactive gases such as argon or nitrogen. Using such methods has been shown to develop secondary phases within the alloy. The thermal spraying can then melt the particles, which can quench on a surface being coated, thereby providing a coating that may be substantially or entirely amorphous.
During use, the powders may be sprayed in the conventional manner, using a powder-type thermal spray gun, though it is also possible to combine the same into the form of a composite wire or rod, using plastic or a similar binder, as for example, polyethylene or polyurethane, which decomposes in the heating zone of the gun. Alloy rods or wires may also be used in the wire thermal spray processes. The rods or wires should have conventional sizes and accuracy tolerances for flame spray wires and thus, for example, may vary in size between 6.4 mm and 20 gauge.
By using the manufacturing procedures disclosed herein, the production of the thermal spray alloyed powder can be kept relatively simple and costs minimized. The method described herein can have an advantage of being used to form a composite powder coating as an outer sheath around a core of additional materials, including a cermet type material that does not alloy upon spraying. During the process, the powder may be sprayed using a conventional technique, such as with a powder-type thermal spray gun. Alternatively, it is also possible to combine the same into a composite wire or rod using plastic or a similar binder, which can decompose in the heating zone of the gun. A binder can be, for example, polyethylene or polyurethane. Alloy rods or wires may also be used in the wire thermal spraying process. In one embodiment, the rods or wires can have sizes and accuracy tolerances for flame spray wires, and thus, for example, may vary in size between 6.4 mm and 20 gauges.
Although the compositions may be quite useful in a number of fully alloyed forms, such as, for example, cast, sintered, or welded forms, or as a quenched powder or ribbon or the like, it is especially suitable for application as a coating produced by thermal flame spraying. In such a thermal spray material, the composition should be in alloy form (as distinct from a composite of the constituents) since the desirable benefit is obtained with the maximum homogeneity available therefrom. Alloy powder of size and flowability suitable for thermal spraying is one such form. In a preferred embodiment, such powder may fall in the range between 100 mesh (U.S. standard screen size) (149 microns) and about 2 microns. For example, a coarse grade may be −140+325 mesh (−105+44 microns), and a fine grade may be −325 mesh (−44 microns)+15 microns. The thermal spray material may be used as is or, for example, as a powder blended with another thermal spray powder such as tungsten carbide.
In addition to coating directly onto the substrate, embodiments also include treating the substrate prior to thermally spraying the bulk-solidifying amorphous alloy. For example, the substrate surface can be modified to provide greater adhesion with the coating, such as by blasting or etching (chemical or vapor), or by treatment with an energy source. An additional brazing material also may be applied to the surface, including a thin foil of bulk-solidifying amorphous alloy. The substrate and brazing material then can be heated to join the brazing to the surface of the substrate. In an embodiment, the brazing material includes at least one, and in other embodiments more than one element in common with the bulk-solidifying amorphous alloy coating (e.g., the brazing includes Zr and Ti, and the bulk-solidifying amorphous alloy also includes Zr and Ti). Use of such a brazing or thin foil of the same or similar bulk-solidifying amorphous alloy provides superior coating strength and promotes interdiffusion of some of the alloy elements to promote adhesion of the coating.
Any suitable brazing material can be used in the embodiments, and in one embodiment, the brazing material is an alloy or bulk-solidifying amorphous alloy having the same or similar elements as the bulk-solidifying amorphous alloy that is coated on the surface of the substrate. Such brazing materials may include, for example, materials formed according to one or more of the following formulae: Fe_44-75Cr_9-15Ni_0-4.8(Mo,Nb)_7.9-13C_1.6-3B_1.3-4.6W_0-11Ti_0-7Si_0-1.1Mn_0-1.1; (Fe_61-75Cr_9-14.4Ni_0-4.8(Mo,Nb)_6-11.7C_1.6-2.1B_1.3-4.6W_0-9.98Ti_0-7Si_0-1.1Mn_0-1.1)_100-xAl_xwhere x ranges from 0.5-10; Fe_62-66Cr_13-25(MO,Nb)_4-12(C,B)_2.2-4.4Ni_0-4.8Si_0-1.5Mn_0-1.2W_0-3.8; Fe_61-76Cr_9-14.4Ni_0-5(Mo,Nb)_7.9-11.7C_1.6-2.1B_1.3-5W_0-9.98Ti_0-7Si_0.1.1Mn_0-1.1; and Fe_62-66Cr_13-25(Mo,Nb)_4-12(C,B)_0-4.4Ni_0-5Si_0-1.5Mn_0-1.2W_0-3.8. In other embodiments, the brazing material may comprise a solder or other infiltrating material that is capable of infiltrating the thermal spray coating under appropriate process conditions.

Critical Casting Thickness

Determining the critical casting thickness of the particular bulk-solidifying amorphous alloy material can be carried out using techniques known in the art. In addition, the relationship between the critical casting thickness, or maximum casting thickness, and the critical cooling rate, and the temperature interval between glass transition temperature and crystallization temperature can be determined for the bulk-solidifying amorphous alloys described herein. FIG. 5 is representative of a graph that can be made showing this relationship, and is excerpted from Nowosielski, et al., Fabrication of Bulk Metallic Glasses by Centrifugal Casting Method,” Journal of Achievements in Materials and Manufacturing Engineering, Vol. 20, pp. 487-490 (2007).
The bulk-solidifying amorphous alloy has several characteristic temperatures, including glass transition temperature Tg, crystallization temperature Tx, and melting temperature Tm. In some embodiments, each of Tg, Tx, and Tm, can refer to a temperature range, instead of a discrete value; thus, in some embodiments the term glass transition temperature, crystallization temperature, and melting temperature are used interchangeably with glass transition temperature range, crystallization temperature range, and melting temperature range, respectively. As shown in FIG. 5, as the temperature differential between glass transition temperature and crystallization temperature increases, the critical cooling rate decreases and the critical casting thickness increases. Thus, increasing this temperature differential will make it easier to form a thicker material with less significant cooling. The temperatures Tg, Tx, and Tm are commonly known and can be measured by different techniques, one of which is Differential Scanning calorimetry (DSC), which can be carried out at a heating rate of, for example, about 20° C./min.
In one embodiment, as the temperature increases, the glass transition temperature Tg of an amorphous alloy can refer to the temperature, or temperature ranges in some embodiments, at which the amorphous alloy begins to soften and the atoms become mobile. An amorphous alloy can have a higher heat capacity above the glass transition temperature than it does below the temperature, and thus this transition can allow the identification of Tg. With increasing temperature, the amorphous alloy can reach a crystallization temperature Tx, at which crystals begin to form. As crystallization in some embodiments is generally an exothermic reaction, crystallization can be observed as a dip in a DSC curve and Tx can be determined as the minimum temperature of that dip. An exemplary Tx for a Vitreloy can be, for example, about 500° C., and that for a platinum-based amorphous alloy can be, for example, about 300° C. For other alloy systems, the Tx can be higher or lower. It is noted that at the Tx, the amorphous alloy is generally not melting or melted, as Tx is generally below Tm.
Finally, as the temperature continues to increase, at the melting temperature Tm, the melting of the crystals can begin. Melting is an endothermic reaction, wherein heat is used to melt the crystal with minimal temperature change until the crystals are melted into a liquid phase. Accordingly, a melting transition can resemble a peak on a DSC curve, and Tm can be observed as the temperature at the maximum of the peak. For an amorphous alloy, the temperature difference AT between Tx and Tg can be used to denote a supercritical region (i.e., a “supercritical liquid region,” or a “supercritical region”), wherein at least a portion of the amorphous alloy retains and exhibits characteristics of an amorphous alloy, as opposed to a crystalline alloy. The portion can vary, including at least 40 wt %, at least 50 wt %, at least 60 wt %, at least 70 wt %, at least 80 wt %, at least 90 wt %, at least 99 wt %; or these percentages can be volume percentages instead of weight percentages.
In an embodiment, the AT for the amorphous alloys described herein is within the range of from about 40 to about 250° C., or from about 65 to about 150° C., or from about 75 to about 110° C. It therefore is beneficial to provide a substrate having a thickness greater than the critical casting thickness, or a substrate that serves as an excellent heat sink so that when contacted with the thermally sprayed bulk-solidifying amorphous alloy, the substrate removes heat and effectively cools the sprayed alloy at a sufficient cooling rate to provide a substantially amorphous alloy coating.

Applications of Embodiments

The presently described methods provide significant improvements in wear resistance, surface activity, thermal conductivity, and corrosion resistance over other pre-existing, conventional coating methods. Because of the superior mechanical properties and resistance to corrosion, the presently described methods can be used to coat a variety of devices. For example, the coatings can be used as bearing and wear surfaces, particularly where there are corrosive conditions. The coating can also be used, for example, for coating Yankee dryer rolls; automotive and diesel engine piston rings; pump components such as shafts, sleeves, seals, impellers, casing areas, plungers; Wankel engine components such as housing, end plate; and machine elements such as cylinder liners, pistons, valve stems and hydraulic rams. The coating is a part of a Yankee dryer, an engine piston; pump shaft, pump sleeve, pump seal, pump impeller, pump casing, pump plunger, component, Wankel engine, engine housing, engine end plate, industrial machine, machine cylinder liners, machine pistons, machine valve stems, machine hydraulic rams, or combinations thereof.
Preferably, the method is used to form coatings on housings or other parts of an electronic device, such as, for example, a part of the housing or casing of the device or an electrical interconnector thereof. The method can also be used to manufacture portions of any consumer electronic device, such as cell phones, desktop computers, laptop computers, and/or portable music players. As used herein, an “electronic device” can refer to any electronic device, such as consumer electronic device. For example, it can be a telephone, such as a cell phone, and/or a land-line phone, or any communication device, such as a smart phone, including, for example an iPhone™, and an electronic email sending/receiving device. It can be a part of a display, such as a digital display, a TV monitor, an electronic-book reader, a portable web-browser (e.g., iPad™), and a computer monitor. It can also be an entertainment device, including a portable DVD player, DVD player, Blue-Ray disk player, video game console, music player, such as a portable music player (e.g., iPod™), etc. It can also be a part of a device that provides control, such as controlling the streaming of images, videos, sounds (e.g., Apple TV™), or it can be a remote control for an electronic device. It can be a part of a computer or its accessories, such as the hard driver tower housing or casing, laptop housing, laptop keyboard, laptop track pad, desktop keyboard, mouse, and speaker. The coating can also be applied to a device such as a watch or a clock.
While the invention has been described in detail with reference to particularly preferred embodiments, those skilled in the art will appreciate that various modifications may be made thereto without significantly departing from the spirit and scope of the invention.

Claims

What is claimed:

1. A method of coating a substrate with a bulk-solidifying amorphous alloy comprising:

providing a substrate having a thickness greater than the critical casting thickness of the bulk-solidifying amorphous alloy; and

thermal spraying the bulk-solidifying amorphous alloy on at least one surface of the substrate,

wherein the substrate has a thickness, and a temperature so that the thermally sprayed alloy cools fast enough to avoid substantial crystallization, thereby providing a substrate coated with the bulk-solidifying amorphous alloy in substantially amorphous form.

2. The method of claim 1, wherein thermally spraying comprises using a high velocity thermal spraying process selected from the group consisting of flame spraying, high-velocity oxy-fuel coating spraying (HVOF), plasma spraying, or combinations thereof.

3. The method of claim 2, wherein the high velocity thermal spraying process is a high-velocity oxy-fuel coating process.

4. The method of claim 1, wherein the coating has a thickness of from about 0.005 to about 0.08 inches.

5. The method of claim 1, wherein the least one surface coated with the bulk-solidifying amorphous alloy has a Vickers hardness of at least about 800 HV-100 gm.

6. The method of claim 1, wherein the substrate has a thickness in the range of from about 1 to about 100 mm, and is provided at about room temperature.

7. The method of claim 1, wherein the coating is at least about 98% amorphous.

8. The method as claimed in claim 1, wherein the bulk-solidifying amorphous alloy is described by the following molecular formula: (Zr, Ti)_a(Ni, Cu, Fe)_b(Be, Al, Si, B)_c, wherein “a” is in the range of from 30 to 75, “b” is in the range of from 5 to 60, and “c” is in the range of from 0 to 50 in atomic percentages.

9. The method as claimed in claim 1, wherein the bulk-solidifying amorphous alloy is described by the following molecular formula: (Zr, Ti)_a(Ni, Cu)_b(Be)_c, wherein “a” is in the range of from 40 to 75, “b” is in the range of from 5 to 50, and “c” is in the range of from 5 to 50 in atomic percentages.

10. The method as claimed in claim 1, wherein the bulk solidifying amorphous alloy can sustain strains up to 1.5% or more without any permanent deformation or breakage.

11. The method of claim 1, wherein the substrate is a substrate of an electronic device.

12. The method of claim 11, wherein the device is an electronic device selected from the group consisting of a telephone, a cell phone, a land-line phone, a smart phone, an electronic email sending/receiving device a television, an electronic-book reader, a portable web-browser, a computer monitor, a DVD player, a Blue-Ray disk player, a video game console, a music player, a device that provides controlling the streaming of images, videos, and sounds, a remote control, a watch, and a clock.

13. A method of coating a substrate with a bulk-solidifying amorphous alloy comprising:

providing a powder alloy composition of a bulk-solidifying amorphous alloy to a thermal spray apparatus;

providing a substrate;

thermally spraying a relatively uniform coating of the bulk-solidifying amorphous alloy onto at least a surface of the substrate such that the coating layer cools sufficiently rapidly to avoid substantial crystallization, thereby providing a substrate coated with a substantially amorphous bulk-solidifying amorphous alloy.

14. The method of claim 13, wherein thermally spraying comprises using a high velocity thermal spraying process selected from the group consisting of flame spraying, high-velocity oxy-fuel coating spraying (HVOF), plasma spraying, or combinations thereof.

15. The method of claim 13, wherein the coating is at least about 98% amorphous.

16. The method as claimed in claim 13, wherein the bulk-solidifying amorphous alloy is described by the following molecular formula: (Zr, Ti)_a(Ni, Cu, Fe)_b(Be, Al, Si, B)_c, wherein “a” is in the range of from 30 to 75, “b” is in the range of from 5 to 60, and “c” is in the range of from 0 to 50 in atomic percentages.

17. The method as claimed in claim 13, wherein the bulk-solidifying amorphous alloy is described by the following molecular formula: (Zr, Ti)_a(Ni, Cu)_b(Be)_c, wherein “a” is in the range of from 40 to 75, “b” is in the range of from 5 to 50, and “c” is in the range of from 5 to 50 in atomic percentages.

18. A method of coating a substrate with a bulk-solidifying amorphous alloy comprising:

providing a substrate having a thickness greater than the critical casting thickness of the bulk-solidifying amorphous alloy;

depositing a brazing layer on the substrate;

optionally heating the substrate and brazing layer to fuse the brazing layer to the substrate, and then optionally cooling the fused substrate and brazing layer; and

wherein the substrate and fused brazing layer has a thickness so that the thermally sprayed alloy cools fast enough to avoid substantial crystallization, thereby providing a substrate coated with the bulk-solidifying amorphous alloy in substantially amorphous form.

19. The method of claim 18, wherein thermally spraying comprises using a high velocity thermal spraying process selected from the group consisting of flame spraying, high-velocity oxy-fuel coating spraying (HVOF), plasma spraying, or combinations thereof.

20. The method of claim 18, wherein the coating is at least about 98% amorphous.

21. The method of claim 18, wherein the substrate has a thickness in the range of from about 1 to about 100 mm.

22. The method as claimed in claim 18, wherein the bulk-solidifying amorphous alloy is described by the following molecular formula: (Zr, Ti)_a(Ni, Cu, Fe)_b(Be, Al, Si, B)_c, wherein “a” is in the range of from 30 to 75, “b” is in the range of from 5 to 60, and “c” is in the range of from 0 to 50 in atomic percentages.

23. The method as claimed in claim 18, wherein the bulk-solidifying amorphous alloy is described by the following molecular formula: (Zr, Ti)_a(Ni, Cu)_b(Be)_c, wherein “a” is in the range of from 40 to 75, “b” is in the range of from 5 to 50, and “c” is in the range of from 5 to 50 in atomic percentages.