IE940157A1 - Composite compacts and methods of making them - Google Patents

Abstract

A method for making a polycrystalline diamond composite compact (10) comprises subjecting a mass of diamond crystals adjacent to a cemented carbide substrate (20) containing a cobalt catalyst, to a high pressure, high temperature process in the region where diamond is thermodynamically stable, which results in a compact characterized by diamond-to-diamond bonding and bonding of the polycrystalline diamond mass to the cemented carbide substrate. The process comprises placing the starting diamond particles onto the carbide substrate in the form of diamond tape (24) containing a binder instead of loose particles, thereby minimizing particle segregation and associated stress concentrations.

Description

Background This invention relates in general to polycrystalline diamond cutting or drilling composite compacts .

More specifically, this invention relates to a method of making polycrystalline diamond or cubic boron nitride (CBN) composite compacts that are more consistent and impact resistant than compacts made as taught in the prior art. This method combines tape casting technology and ultra high pressure/temperature (HP/HT) processing to form these strong coherent composite compacts.

Composite polycrystalline diamond compacts (PDC) composed of ultra hard particles (diamond or cubic boron nitride) sintered and bonded to a cemented tungsten carbide substrate are widely used in industry as cutting tools, drill bit cutters, dressing tools, wire drawing dies and other wear parts. Many commercially available PDC or CBN composite compacts are made according to the teachings of U.S. Patent Number 3,745,623 whereby a relatively small volume of super hard particles is sintered as a thin layer (approx. 0.5 to 2.5 mm.) onto a substantially thicker planar layer of pre-cemented carbide.

Although this method proves satisfactory for many wear part applications, the difficulty in maintaining 4 0 1 5 7 a -2a homogenous particle size distribution creates high residual stresses in the abrasive layer and at its interface with the cemented carbide mass. These high stress concentrations lead to unduly high manufacturing rejection rates or high tool breakage rates when used under impact conditions.

U.S. Patent Numbers 4,604,106 and 4,811,801 the entire disclosures of which are incorporated herein by reference, teach the use of transitional layers of diamond particles admixed with pre-cemented carbide particles. These transition layers create a gradient of the diamond/carbide particles to provide a closer match of thermal expansion at the diamond layer and carbide substrate interface. The cemented carbide particles vary in concentration from zero volume percent at the working surface of the tool to approximately 60 volume percent at the carbide substrate interface.

Although this transition layer method does provide superior bonding and impact properties of finished compacts for most applications, there are consistency problems in their manufacture. Even when sintering or bonding various concentrations of diamond and carbide particles to a planar surface of a carbide substrate, it is very difficult to consistently pour ultra fine loose diamond and pre-cemented carbide particles into a HP/HT reaction vessel mold cavity without undesirable segregation and redistribution of the particles because of the disparity of their particle sizes and specific gravity. This sometimes causes high stress concentrations and unpredictable physical properties with ultimate failure or rejection of the compact.

Sometimes it is desirable to sinter diamond/carbide transition layers to a pre-cemented carbide substrate having a non-planar or asymmetric bonding surface such as a hemisphere, truncated cone or other shapes. Bonding discrete transition layers of 4 0 15 7 si -3diamond/carbide particles to a carbide substrate having such geometries using loose diamond/carbide powder is quite difficult. Other means, such as grease, wax or other viscous and heat vaporizing materials are employed as temporary binders for the various blends of diamond and carbide particles needed for any particular application. The blend of temporary binder material, diamond and carbide particles are then applied in the desired thickness on either the male carbide substrate bonding surface or on the mating female surface of the mold cavity. The carbide substrate is properly assembled in the mold cavity with the diamond/carbide particles and temporary binder sandwiched between the substrate bonding surface and a complementary female mold cavity contoured form. The assembly is then processed in a HP/HT press cycle. The temporary binder material is volatilized and the diamond/carbide particle mass is sintered and bonded to the carbide substrate.

While this method of fabrication produces compacts that are significantly superior to compacts made by prior art teachings, there are problems in fabrication. It is time consuming and highly skilled manpower intensive to hand shape the viscous binder/diamond/carbide mass to the correct thickness and position prior to sintering. This leads to a higher than desired reject and product failure rates.

The present invention is directed to a method of producing a polycrystalline diamond composite compact using the techniques and processes commonly referred to as tape casting, in conjunction with High Pressure/High Temperature (HP/HT) diamond synthesis technology. Tape casting is most commonly used in the electronics industry to fabricate ceramic coatings, substrates and multilayer structures. Fine ceramic powder is mixed with a temporary binder. The binder can be either natural or synthetic high molecular 9401571 -4weight substances such as starches, dextrins, alcohols, cellulose, gums and some polymers. The ceramic powder/binder mixture is mixed and milled to the most advantageous viscosity, rheology and homogeneity. It then is rolled into a strip or tape of the desired thickness .

The tape is then dried to remove the water or other volatile carriers. The dried tape is flexible and strong enough in this state to be handled and cut into the shapes needed to conform to the geometry of the substrate onto which it is to be bonded using a temporary adhesive. The tape/substrate assembly is then heated in a suitable furnace initially to a temperature high enough to drive the temporary adhesive and/or binder material off as volatiles. The temperature is then raised to a level where the ceramic powders fuse together and to the substrate, producing a very uniform continuous ceramic coating bonded to the substrate .

U.S. Patent Numbers 4,329,271 and 4,353,958 are examples of making ceramic cast tapes and U.S. Patent Number 3,518,756 is an example of using ceramic cast tapes to fabricate micro-electric structures.

A technical paper on tape casting technology written by Rodrigo Mareno - Instituto de Ceramica y Vedrio, CSIC - Madrid, Spain - in two parts - Volume 71, No. 10 (October 1992) and Volume 71, No. 11 (November 1992) in the American Ceramic Society Bulletin is a comprehensive discussion on the technical means of ceramic tape management utilizing the various ramifications of ceramic tape control processes.

U.S. Patent Numbers 3,743,556; 3,778,586; 3,876,447; 4,194,040 and 5,164,247 describe the use of similar tape casting technology employing a polymer temporary binder, such as polytetrafluoroethylene (PTFE), binding hard facing powder, such as tungsten carbide or the like, and a relatively low melting 9401571 -5brazing alloy powder into tape form. This tape is used to produce a wear or erosion resistant carbide layer brazed onto a metallic substrate when heated to the liquidus temperature of the brazing alloy.

Summary of the Invention The present invention provides a method of forming and sintering a composite compact having a polycrystalline ultra hard particle mass bonded to a cemented metal carbide substrate. One or more laminates comprising a tape casting binder containing ultra hard particles is temporarily adhered to the surface of the carbide substrate. The substrate with the laminate temporarily adhered thereto is processed in a high pressure, high temperature diamond synthesis apparatus for sintering the ultra hard particles to each other while bonding the polycrystalline ultra hard particle mass to the cemented metal carbide substrate.

A benefit of the present invention over the prior art methods of producing polycrystalline diamond composite compacts, is the diamond can be uniformly distributed on the metal carbide substrate bonding surface even though it is not planar. For example, this bonding surface can be convex, concave, hemispherical, asymmetrical or other non-planar conf igurat ion. 940157! -6Brief Description of the Drawings These and other advantages and features of the present invention will be better understood upon review of the following detailed description of the preferred embodiments read in conjunction with the accompanying drawings wherein: FIGURE 1 is a partially sectioned exploded isometric view of the HP/HT vessel and components used to fabricate the embodiment of the invention shown in Figure 2; FIGURE 2 is a partial cross-sectional view of an embodiment of the present invention and the HP/HT confining vessel in which it was fabricated; and FIGURE 3 is an enlarged portion of cross-section 3 of Figure 2. ^•40157 -7Description Figure 1 illustrates the unassembled components of a High Pressure/High Temperature (HP/HT) diamond synthesis reaction vessel 30 of Figure 2 used to fabricate a polycrystalline diamond composite compact 10 such as an insert for a conventional rock bit used for oil well drilling. A cylindrical mold cavity bore 12 is formed centrally in a refractory material 11, such as, for example, molybdenum. A refractory material end plug 16 or cap which has a snug fit into mold bore 12 is used to confine the mold assembly 3 0 axially. The mold cavity top surface 14 as illustrated is, for example, a female rounded oblique conical surface that forms a finished male convex outer sintered polycrystalline diamond surface 26 on the compact illustrated in Figure 2. Shapes such as right cylinders, right circular cones, various asymmetrical shapes, hemispheres or other surfaces of complex geometry may be fabricated without departing from the intent and scope of the present invention.

The cemented carbide substrate 20 of the compact has a cylindrical body surface 21 being a slip fit in the mold bore 12. The substrate also has a base end surface 23 and a head end surface 22. The head end surface 22 is a male rounded oblique conical surface that is reduced in all three dimensions so that the clearance between this surface and the complementary mold cavity top surface 14 is such that the final sintered composite diamond layer is compacted to a predetermined thickness.

Flexible pre-formed diamond tape layers 24a,b,c are cut to shape so that each layer smoothly covers the entire head end surface 22. The diamond layers 24, for example, are temporarily affixed to the substrate head end surface 22 and sequentially are secured to each other with a heat volatile adhesive. -89 4 0 15 7 e? Diamond containing tapes may formulated using water compatible binder systems such as high molecular weight cellulose derivatives, starches, gums, dextrins, alcohols and other natural or synthetic systems. Polymer systems such as polyacrylonitrile, polyethylene, polyvinyl alcohol, polycarbonate polypropylene using various solvents and dispersants have also been formulated and tested.

Such tapes have diamond or diamond and metal carbide particles distributed in and secured together with such a binder. Preferably, the amount of binder is just sufficient to hold the particles together and yield a flexible tape that can be handled, cut, formed and adhered to a substrate. Generally, all of the void space between particles is effectively filled with binder.

Green diamond tapes are processed using standard extrusion, injection molding, pressing or tape casting equipment. Diamond tape castings, so made, exhibit uniform thickness, flexibility, good surface finish and predictable and dense diamond volumetric concentration. Diamond tapes, having such uniform diamond particle size distribution, are consistently made from about 0.1 to about 2 mm. thick as needed for any given application.

The temporary assembly of carbide substrate 20, diamond tape overlays 24 and mold cavity end plug 16 are firmly pressed into the mold bore 12 and aligned radially to match the contour of the mold cavity top surface 14 and the contour of the top diamond layer surface 26. This ensures the proper compaction and distribution of the composite diamond layer 24.

The diamond layers may have different compositions. For example, the outermost layer 24a may have solely diamond particles in the tape. The diamond particles may have any of a broad range of particle Ik® 4 0 1 5 7 -9sizes from a micrometer or less to several micrometers.

A blended mixture of sizes is often preferred.

The next layer 24b comprises a mixture of diamond and tungsten carbide particles with a higher proportion of diamond than carbide. The innermost layer adjacent to the carbide substrate is also a mixture of diamond and tungsten carbide particles, with a higher proportion of carbide than diamond for more closely matching the properties of the carbide substrate. The inner layers 24b and 24c provide transition in properties as well as composition between the carbide substrate and the outermost polycrystalline diamond layer in the final compact.

In the embodiment illustrated the head end surface of the insert is convex and layers are applied to the complexly curved convex end. If desired, a similar technique may be used for applying layers to flat or concave surfaces .

The pressure cell assembly 3 0 is then heated in vacuo to drive off moisture, adhesives and temporary diamond tape binders. The diamond and carbide particles in the tapes remain in place because trapped in the mold cavity next to the head end surface.

After pre-heating, the pressure cell 30 is placed in a conventional HP/HT diamond synthesis press. The pressure, then temperature are increased to the thermodynamically stable region of diamond. Under this set of conditions, cobalt migrates from the cemented tungsten carbide substrate 20 into the diamond layer 24 and acts as a solvent/catalyst of the elemental carbon of the diamond to promote polycrystalline diamond to diamond bonding. Nickel or iron may be substituted for the cobalt without departing from the scope of this invention. The cobalt or other metal binder also provides a chemical bond of the tungsten carbide particles to the surrounding diamond particles in the diamond layer 24. The cobalt also provides a strong -10chemical bond of the composite diamond layer 24 to the tungsten carbide substrate head end surface 22.

If it is desirable, the catalyst/binder (cobalt, nickel or iron) can be supplied to the composite diamond layer 24 by placing a thin sheet of the preferred metal at the diamond tape casting layer 24 and substrate surface 22. The catalyst/binder metal can also be supplied as a discrete powdered metal tape casting layer or the powdered metal can be admixed with the diamond particles in the tape castings. Another means to supply the diamond layer/carbide substrate system with catalyst/binder metal is to plate the tungsten carbide substrate head surface 22 with the preferred metal binder using either electroplating, chemical vapor deposition (CVD) or physical vapor deposition (PVD).

Figure 3, which is an enlarged portion of cross section 3 of Figure 2, shows the individual diamond tape casting layers 24a,b,c sintered into a coherent polycrystalline mass which is chemically bonded to the carbide substrate head end surface 22. The discrete tape casting layers 24a,b,c shown in Figure 1, have been transformed in the HP/HT process into a continuous mass with diamond crystal growth and inter crystalline bonding. Also shown is the commingling of the diamond/carbide particles at the layer interfaces to produce very uniform transition layers.

When a gradient of particle sizes and/or densities are needed to reduce stress concentrations, caused by indiscriminate mixing of diamond and/or carbide metal particles, discrete thin tapes of sequentially increasing or decreasing diamond and metal carbide particle size and/or density are stacked to achieve a predetermined particle distribution in the sintered composite compact abrasive layer. Thus, complete control of the diamond-carbide distribution is achieved when sintering a diamond particle mass or a diamond and 4 0 1 5 7 4 -11metal carbide mass to either a planar or non-planar cemented carbide substrate surface by using stacked diamond tape castings of differing compositions.

There has thus been described a method to fabricate a polycrystalline diamond composite compact that has a multilayered diamond mass sintered and chemically bonded to a complex presintered cemented tungsten carbide substrate surface according to the present invention. Even though the illustrated example of the diamond mass was formed of multiple diamond tape castings, a single layer tape casting can be used to advantage in some applications for minimizing diamond and/or carbide particle segregation of mixed particle sizes or particles having differing densities.

Although much of the description has involved the use of cobalt bonded tungsten carbide as the substrate material, other cemented metal carbides, as well as other types of materials are within the scope of the present invention. For instance, cubic boron nitride (CBN) polycrystalline composite compacts can be produced using the aforesaid basic principles, although at times a different catalyst/solvent. may be used for some purposes. The ultra hard particles may be either diamond or CBN.

Instead of placing the laminate or laminates of tape directly on the substrate, they may first be placed in a mold complementary to the shape of the substrate or final compact to be formed. The substrate is then pressed in place against the laminates in the mold and this assembly is processed in the same manner described.

Clearly, the scope of the present invention is not limited to this description of the preferred embodiments. All modifications which are within the ordinary skill in the art to make are considered to be within the scope of the invention as defined by the appended claims .

Claims (9)

CLAIMS:

1. A method of forming and sintering a composite compact having a polycrystalline ultra hard particle mass bonded to a cemented metal carbide substrate comprising the steps of: temporarily adhering to the surface of the substrate, one or more laminates of a flexible tape comprising a binder containing ultra hard particles; and processing the substrate with the laminate temporarily adhered thereto in a high pressure, high temperature diamond synthesis apparatus, for sintering the ultra hard particles to each other while bonding the sintered ultra hard particle mass to the cemented metal carbide substrate to form the composite compact.

2. A method as recited in claim 1 comprising placing a plurality of laminates on the surface of the substrate, the outermost laminate containing substantially entirely ultra hard particles and a laminate between the outermost laminate and the substrate comprising a mixture of ultra hard particles and metal carbide particles.

3. A method as recited in either of claims 1 or 2 further comprising the steps of: placing the substrate in a mold complementary to the shape of the substrate with the laminate in place on its surface; and heating the mold and compact sufficiently for removing temporary binders from the laminate before processing in a high pressure, high temperature diamond synthesis apparatus. »•40157* -134. A method as recited in any of the preceding claims wherein the adhering step comprises placing the laminate in a mold complementary to the shape of the substrate and placing the substrate against the laminate.

4. 5. A method as recited in claim 1 wherein the compact comprises a rock bit insert having a generally cylindrical body and a convexly curved head end and the step of applying a laminate comprises applying laminate to the convex surface of the head end.

5. 6. A method as recited in any of the preceding claims comprising including cobalt in the tape laminate .

6. 7. A method as recited in any of the preceding claims wherein the ultra hard particles are selected from the group consisting of diamond and cubic boron nitride .

7. 8. A method of forming and sintering a composite compact having a polycrystalline ultra hard particle mass bonded to a cemented metal carbide substrate substantially as herein described with reference to the accompanying drawings.

8.

9. A composite compact made according to the method in any of the preceding claims.