WO2004096469A1

WO2004096469A1 - A metal powder composition

Info

Publication number: WO2004096469A1
Application number: PCT/SG2004/000112
Authority: WO
Inventors: Li Lu; Ying Hsi Jerry Fuh; Yoke San Wong; Han Tong Loh; Haihong Zhu; Yaxin Tang; Xinhua Wang
Original assignee: National University Of Singapore
Priority date: 2003-04-29
Filing date: 2004-04-29
Publication date: 2004-11-11

Abstract

A metal powder composition is disclosed. The metal powder composition can be used as a material in a sintering process. The composition comprises a first metal powder comprising copper having a first mean particle size; a second metal powder comprising copper and having a second mean particle size that is less than the first mean particle size; and a third metal powder capable of melting at a temperature that is lower than the melting temperatures of the first and second metal powders and having a third mean particle size less than the first and second mean particle sizes.

Description

A Metal Powder Composition

Technical Field

The present invention generally relates to a metal powder composition. The present invention also relates to a metal powder composition that may be sintered and to a sintering method.

Background "Rapid prototyping" is the name- given to a host of related technologies that are used to fabricate physical objects directly from CAD data sources. The .methods directly build three-dimensional (3-D) objects from computer-aided design (CAD) data in a layer by layer fashion. H 1

The material density of a metal product significantly affects its mechanical properties . Accordingly, the fabrication of 3-D metal parts using rapid prototyping methods aims to produce metal parts that are dimensionally accurate and which have a relatively high density. The fabrication of 3-D metal parts using rapid prototyping methods in which powdered metals are subjected to sintering have been investigated. However, these fabrication techniques have been hampered somewhat by the produced metal products being susceptible to warpage and low material density.

The apparent density of metal powders is generally within the range of 20-70%, thus it is necessary for the metal product to undergo a densification step in the metal powder forming process. However, the densification step has resulted in shrinkage of the metal product, which may lead to warpage and reduced dimensional accuracy. Warpage can also lead to mechanical failure of objects produced from the metal powders by the rapid prototyping techniques ..

One known fabrication technique is called "Selective Laser Sintering" (SLS) and involves depositing a powder material onto the surface of an article and then thermally liquefying the powder material and the surface of the article by focusing a relatively high power continuous-wave laser beam thereon. The high power laser is removed and the liquefied surface allowed to cool and thereby solidify to bond the metal layer to the article. Although metal parts fabricated by these techniques may have a high density, the required laser power and beam quality are usually high. The laser power is normally higher than 1 kW. In addition, the process itself induces high thermal stress that may cause distortion and may limit the accuracy and size of the sintered parts . These drawbacks can be reduced by additional processing steps, such as milling, grinding, sand blasting and the like. However the additional processing steps can render these techniques quite expensive. Furthermore, the use of a high power laser and its associated control system may also render these techniques expensive.

One type of SLS process is called direct laser metal sintering (DLMS) and is disclosed in WO-90/11855. Although this process produced parts having high dimensional accuracy, they were found to be highly porous, having a relative density of 60-70%. Attempts have been made to increase the density of products made by this method by sintering in a gas atmosphere in the presence of a chemical compound of an iron- group metal. However, the complex equipment and control system limits the application of this technique.

There is a need to provide a metal powder composition that is capable of being sintered and which overcomes, or at least ameliorates, one or more of the disadvantages described above .

There is a need to provide a method and a material system for fabricating metallic parts with high density and low shrinkage. There is a need to provide a metal powder composition which can be sintered using a relatively lower powered laser.

There is a need to provide a metal powder composition that is capable of being sintered under atmospheric conditions and without pre-heating.

Summary of invention

According to a first aspect of the invention, there is provided a metal powder composition comprising: a first metal powder comprising copper and having a first mean particle size; a second metal powder comprising copper and having a second mean particle size that is less than the first mean particle size; and a third metal powder capable of at least partially melting at a temperature that is lower than the melting temperatures of the first and second metal powders and having a third mean particle size less than the first and second mean particle sizes.

The metal powder may be homogenous or non-homogenous .

In one embodiment, the present invention provides a metal powder composition capable of being sintered comprising: a first metal powder comprising Cu or copper alloy and having a first mean particle size,- a second metal powder comprising Cu or copper alloy and having a second mean particle size that is less than the first particle size; and a third metal powder comprising copper alloy and having at least a partial melting temperature that is less than the first and second metal powders and having a third mean particle size less than the first and second mean particle sizes; wherein upon sintering, the metal powder forms a metal product having a relative density of 70% or more. In another embodiment, the present invention provides a metal powder composition comprising: about 30% to about 70% by weight of a first metal powder comprising Cu or copper alloy, the first metal powder having a mean particle size in the range between about 50μm to about 90μm; about 5% to about 20% by weight of a second metal powder comprising Cu or copper alloy, the second metal powder having a particle size in the range between about 25μm to about 45μm; and the remainder being substantially a third metal powder, the third metal powder having a mean particle size in the range between about lμm to about 25μm and wherein the ratio of the melting temperature of the first and second metal powders to the melting temperature of the third metal powder is about 3 or less .

According to a second aspect of the invention, there is provided a method of preparing a metal powder composition, the method comprising the steps of: providing a first metal powder comprising Cu and having a first mean particle size; providing a second metal powder comprising Cu and having a second mean particle size that is less than the first particle size; providing a third metal powder capable of at least partially melting at a temperature that is lower than the melting temperatures of the first and second metal powders and having a third mean particle size less than the first and second mean particle sizes; and combining the first metal powder, the second metal powder and the third metal powder to form the metal powder composition.

According to a third aspect of the invention, there is provided a sintered metal product prepared by sintering a metal powder composition, the metal powder composition comprising: a first metal powder comprising copper and having a first mean particle size; a second metal powder comprising copper and having a second mean particle size that is less than the first particle size; and a third metal powder capable of at least partially melting at a temperature that is lower than the melting temperatures of the first and second metal powders and having a third mean particle size less than the first and second mean particle sizes.

In one embodiment, there is provided a sintered metal product prepared by sintering a metal powder composition, the metal powder composition comprising: a first metal powder comprising copper and having a first mean particle size; a second metal powder comprising copper and having a second mean particle size that is less than the first particle size; and a third metal powder capable of at least partially melting at a temperature that is lower than the melting temperatures of the first and second metal powders and having a third mean particle size less than the first and second mean particle sizes; wherein the metal powder composition is sintered at a pressure in the range of about 70kPa to about 120 kPa absolute pressure; wherein the metal powder composition is sintered at a temperature in the range of about 600 °C to about 1200 °C; and wherein the composition of the gas surrounding the metal powder composition as it is sintered is substantially that of air.

According to a fourth aspect of the invention, there is provided a sintering method comprising: sintering a metal powder composition comprising: a first metal powder comprising copper and having a first mean particle size; a second metal powder comprising copper and having a second mean particle size that is less than the first particle size; and a third metal powder capable of at least partially melting at a temperature that is lower than the melting temperatures of the first and second metal powders and having a third mean particle size less than the first and second mean particle sizes to provide a sintered metal product.

According to a fifth aspect of the invention, there is provided a sintered metal product prepared by the fourth aspect .

According to a sixth aspect of the invention, there is provided the use of a metal powder composition in a sintering process, the metal powder composition comprising: a first metal powder comprising copper and having a first mean particle size; a second metal powder comprising copper and having a second mean particle size that is less than the first particle size; and a third metal powder capable of at least partially melting at a temperature that is lower than the melting temperatures of the first and second metal powders and having a third mean particle size less than the first and second mean particle sizes.

Definitions

The following words and terms used herein shall have the meaning indicated: The term "relative density" is the ratio of the density of a sintered metal to the theoretical density of the starting powder, which is defined as follows:

Prelative density ⁼ Psintered/ P theoretical XJ- O O -S where

P_snere is the density of sintered metal given as :

Psintered MaSS (ainte red metal) /Vθlume (_{s ntered me}tal> where :

M is the mass of the sintered part, V is the volume of the sintered part (include porosity)

Ptneor_eti_cai is the theoretical density of the metal powder composition and is given as :

Pt_heoretical = ( Pi V;, +p₂ V₂ + p₂ V₃ ) where:

Pi is the theoretical density of the ith powder, which is 8.92 g/cm³ for Cu at 25 °C;

Vi is the volume percent of the ith powder in the starting powder.

The term "apparent density" generally refers to the mass (m) of a solid substance divided by its volume (v' ) (ie. m/V ) , wherein v' includes the open pores of a solid substance but excludes the closed pores of the solid substance.

The term "melting temperature" generally refers to the temperature at which a solid transforms into a liquid.

The terms "partially melting" or "partial melting" and grammatical variations thereof are to be interpreted broadly to be the point at which the alloy is not completely solid but has at least begun to melt. The term "eutectic temperature" generally refers to the lowest temperature at which an alloy solid will melt to form a liquid phase.

The term "incidental impurities' refers to any material that may be present in the raw materials used to produce copper or an alloy that includes copper. Incidental impurities include unavoidable impurities as well as avoidable impurities .

Disclosure of embodiments

Exemplary non-limiting embodiments of a metal powder composition will now be disclosed. The disclosed embodiments relate to a metal powder composition that is capable of being sintered directly by a laser.

The disclosed embodiments describe a novel powder composition that includes a first metal powder, a second metal powder, and a third metal powder. The first metal powder contains Cu or a Cu alloy and has a first mean particle size. The second metal powder also contains Cu or a Cu alloy and has a second mean particle size that is less than the first particle size. The third metal powder is composed of a metal or metal alloy that is capable of melting at a temperature that is lower than the melting temperatures of the first and second metal powders. Upon sintering, the metal powder forms a metal product having a relative density of 70% or more.

The first and second metal powders

The first and second metal powders may have the same or different compositions.

In one embodiment, the first and second metal powder may substantially comprise Cu and any incidental impurities. The purity of the Cu may be up to 99.99% pure copper. In another embodiment, the first and second metal powder may comprise a Cu-containing alloy. The amount of copper within the Cu-containing alloy may be a range by weight selected from the range consisting of: 30% to 99%, 40% to 96%, 50% to 94%, 55% to 92%, 60% to 90%, 60% to 94%, 60% to 90%, 60% to 88%, and 60% to 85%. The remainder may be one or more metals and any incidental impurities .

The metals other than Cu that may be present in the Cu- containing alloy may be selected from the group consisting of: chromium, cobalt, lead, manganese, molybdenum, nickel, silver, tin, tungsten, zinc, and one or more mixtures thereof.

One or more additional additives may also be added to the Cu-containing alloy. The additives may be selected from the group consisting of: aluminum, beryllium, bismuth, cadmium, carbon, iron, magnesium, niobium, phosphorous., silicon, tantalum, vanadium, zirconium and one or more mixtures thereof. The amount of additives within the Cu- containing alloy may be, by weight, selected from the range consisting of: 0.02% to 4%, 0.2% to 2%, 0.2% to 1%, 0.4% to 1.5%, and 0.5% to 1%.

The melting temperature of the first and second metal powders may be within the range selected from the group consisting of: 900°C to 1600°C; 1000°C to 1500°C; 1100°C to 1300°C; and 1150°C to 1250°C.

In other embodiments, the first and second metal powders may contain mixtures of copper and copper-containing alloy.

The particle size range of the first metal powder may be selected from the group consisting of: 40μm to lOOμm; 45μm to lOOμm; 50μm to lOOμm; 50μm to 95μm; 55μm to 90μm; 55μm to 85μm; and 60μm to 80μm. The mean particle size of the first metal powder may be in the range selected from the group consisting of: 50μm to 90μm; 55μm to 85μm; and 60μm to 80μm. In one embodiment, the mean particle size of the first metal powder is about 70μm.

The amount of the first metal powder that may be present in the metal powder composition, by weight, may be selected from the group consisting of: 30% to 70%; 40% to 70%; 40% to 65%; and 40% to 60%. In one embodiment, the first metal powder present in the metal powder composition is about 50% by weight .

The particle size range of the second metal powder may be selected from the group consisting of: 20μm to 55μm; 25μm to 50μm; 30μm to 45μm; 30μm to 40μm; and 35μm to 40μm.

The mean particle size of the second metal powder may be in the range selected from the group consisting of: 25μm to 45μm; and 30μm to 40μm. In one embodiment, the mean particle size of the second metal powder is about 38μm.

The amount of the second metal powder that may be present in the metal powder composition, by weight, may be selected from the group consisting of: 5% to 20%; 6% to 18%; 6% to 15%; and 8% to 12%. In one embodiment, the first metal powder present in the metal powder composition is about 10% by weight .

The third metal powder

In one embodiment, the third metal powder has a eutectic temperatures that is lower than the melting temperature of the first or second metal powders .

The composition of the third metal powder may be copper alloy having eutectic temperature less than the melting temperature of the first and second metal powders . In addition to copper, the alloy of the third metal powder may contain additional metals selected from the group consisting of: Ag, Al, Bi, B, Cd, Co, Fe, Mg, Mn, Ni, Pb, Zn, and one or more combinations thereof.

Other elements that may be present in the alloy of the third metal powder may be selected from the group consisting of: P, and Si and one or more combinations thereof.

Exemplary third metal alloys may include Cu-P, Cu-Ag, Cu-P-Ag, Cu-Ag-Zn, .Cu-Zn-Si, Ag-Cu-Zn-Cu.

The Cu-Ag-P alloy composition may be comprised as follows: about 2% to about 20% by weight Ag; about 5% to about 8% by weight P; and the remainder being Cu and any incidental impurities.

Exemplary Cu-Ag-P alloy compositions and their approximate melting temperatures are given in Table 1 below.

Table 1

The melting temperature of the third powder may be within the range selected from the group consisting of: 300°C to 1000°C; 400°C to 950°C; 500°C to 900°C; 550°C to 800°C; and 600°C to 700°C. The ratio of the melting temperature of the first and second metal powders to the melting temperature of the third metal powder may be about 3 or less. In one embodiment, the difference between the melting temperatures of the first and second metal powders and that of the third metal powder is in the range selected from the group consisting of: 300 °C to 900°C; 350°C to 800°C; 350°C to 700°C; and 400°C to 600°C.

The particle size range of the third metal powder may be selected from the group consisting of: lμm to 25μm,- lμm to 20μm; 5μm to 20μm; lOμm to 20μm; and 12μm to 18μm.

The mean particle size of the third metal powder may be in the range selected from the group consisting of : Iμm to 25μm; lOμm to 20μm and 12 μm to 18μm. In one embodiment, the mean particle size of the third metal powder is about 15μm.

The amount of the third metal powder that may be present in the metal powder composition, by weight, may selected from the group consisting of: 23% to 60%; 25% to 65%; 30% to 60%; 30% to 50%; and 35% to 45%. In one embodiment, the third metal powder present in the metal powder composition is about 40% by weight.

Preparation of Powder Composi tion

The particles of the metal powders may be spherical or substantially spherical and/or elliptical in shape. In other embodiments, particles of the metal powders may have an irregular shape or the particles of the metal powders may be a mixture of regular and irregular shapes or the particles of the metal powders may be regular shapes . The metal powders may be gas-atomized metal powders.

The raw materials for the metal powders to be used for the first and second metal powders may be obtained commercially from a number of manufacturers. Exemplary manufacturers from which copper and copper alloy powders may be obtained include: Umicore Canada Inc., of Leduc, Alberta, Canada; ACuPowder International, LLC of Union, New Jersey, United States of America; Crucible Research LLC, of Pittsburgh, Pennsylvania, United States of America; and Kennametal Inc. of Latrobe, Pennsylvania, United States of America.

The raw materials for the metal powders to be used for the third metal powders may be obtained commercially from a number of manufacturers. Exemplary manufacturers from which low melting temperature metal alloy powders may be obtained include: Lucas-Milhaupt Inc., of Cudahy, Wisconsin, United States of America; and Saru Silver Alloys PVT. LTD., of Meerut, Uttar Pradesh, India.

The first, second and third metal powders may be weighed according to the proposed metal powder composition to be prepared. The weighed first, second and third metal powders may be placed into a mixing device where they may be mixed to form a substantially homogenous mixture. The mixing device may be a V-Cone blender. Other exemplary mixing devices include rota-cone blenders, ribbon blenders, cone blenders, kneader mixers and plough shear mixers.

Then the metal powder mixtures may be blended for in a mixing device for a period of time selected from the group consisting of: 5 minutes to 5 hours; 20 minutes to 4 hours; 30 minutes to 3 hours; 45 minutes to 2 hours; and 50 minutes to 1.5 hours.

In one embodiment, the metal powder may be mixed for about 1 hour in a V-cone blender in order to obtain uniform mixture . Sintering processes

The metal powder composition may be densified by a sintering process . Exemplary sintering process that may be used to sinter the disclosed metal powder composition include laser sintering, selective laser sintering or hot isostatic pressing, direct laser sintering, thermal sintering and microwave sintering.

The sintering may be carried out at an absolute pressure in the range selected from the group consisting of: 70 kPa to 120 kPa; 75 kPa to 115 kPa; 80 kPa to 110 kPa; 90 kPa to 105 kPa; and 95 kPa to 105 kPa. In one embodiment, the sintering is carried out at a pressure of about 101.3 kPa.

The sintering may be carried out at temperature in the range selected from the group consisting of: 600 °C to about 1200°C; 625°C to about 1100°C; 650°C to 1000°C; 650°C to 900°C; and 650°C to 800°C.

The sintering may be carried out in the presence of oxygen in the range, by volume, selected from the group consisting of:l% to 25%; 5% to 21%; 10% to 21%; 15% to 21%; and 18% to 21%. In one embodiment, the sintering may be carried out in the presence of air.

Direct laser sintering processes

The metal powder composition may be sintered directly by a laser.

The power of the laser applied directly to the metal powder composition may be in the range selected from the group consisting of: 75W to 400W; 100W to 300W; 100W to 250W.

In one embodiment, the metal powder composition may be sintered directly by a laser at about 200W. The laser may be scanned over the surface of a layer of the metal powder composition. The scan speed of the laser may be in the range selected from the group consisting of: 50 to 500mm/s; 75 to 400mm/s; 100 to 300mm/s; and 150 to 250mm/s. In one embodiment, the scan speed of the laser is about 200 mm/s .

The laser scan spacing may be in the range selected from the group consisting of: 0.05mm to 0.4mm; 0.1mm to 0.3mm; and 0.15mm to 0.25mm. In one embodiment, the scan speed of the laser is about 0.2 mm.

The layer thickness of the metal powder composition that may be subjected to direct laser sintering may be in the range selected from the group consisting of: 0.05mm to 0.2mm;

0.05mm to 0.1mm; and 0.05mm to 0.08mm. In one embodiment, the scan speed of the laser is about 0.075 mm.

Upon sintering the metal powder composition, a metal product is produced. The relative density of the metal product may be in the range selected from the group consisting of: 70% to 100%; 75% to 98%; 78% to 95%; 80% to

95%; 82% to 92%; and 84% to 90%.

Mode(s) of performing disclosed embodiments

Non-limiting examples of the invention, including the best mode, and a comparative example will be further described with reference to the accompanying drawings in which: -

Brief Description Of Drawings Fig. 1 is shows a schematic diagram of an apparatus used in the direct laser sintering process;

Fig. 2 shows the Simultaneous Thermal Analysis (STA) traces of the third powder mixture of Example 1 and pure Cu; Fig. 3 shows the surface morphology of a sintered sample of the composition prepared in example 1;

Fig. 4 shows the microstructure of the sintered sample of the composition prepared in example 1;

Fig. 5 shows a Scanning Electron Microscope (SEM) image of the sintered sample of the composition prepared in example

1;

Fig. 6(a) shows X-ray patterns of the starting powder composition prepared in example 1;

Fig. 6(b) shows X-ray patterns of a sintered sample of the composition prepared in example 1;

Fig. 7 shows a hypothetical model of expansion in plate caused by gravity in direct laser sintering.

Detailed Description of embodiments

Direct laser sintering system

Fig. 1 shows a schematic diagram of the operation of a laser sintering system 10 that can be used to sinter the metal powder composition. Referring to Fig. 1, the system 10 includes a continuous-wave (CW) C0₂ laser 12 operating at a wavelength (λ) equal to 10.6μm and at 200W power. The system 10 also includes a chamber 14 having a controlled atmosphere.

The system 10 also includes a metal powder composition delivery system 16 that includes a powder chamber 18 for holding the metal powder composition, a drive plate 20 at the base of the chamber 18 for moving the metal powder composition in the direction of arrow 22, and a scrapper 24 at the top of the powder chamber 18 for moving a layer of metal powder composition 26 in the direction of arrow 28, towards laser chamber 30. Laser chamber 30 is initially charged with the metal powder composition.

The system 10 also includes a lens 32 in the optical path of laser light being emitted from the laser 12 for focussing the laser light onto scanner 34. The focus of the lens 32 is 370mm with a focused spot size of 0.3mm. The scanner 34 is also provided along the optical path of the laser light and directs the laser light to the surface of the metal powder composition charged within laser chamber 30. The scanner 34 is capable of operating at variable scanning speed.

A preheating device 38 capable of preheating the metal powder within chamber 30 is provided to pre-heat the metal powder to a maximum temperature of 400 °C as a layer of the metal powder composition is passed from scrapper 24 to chamber 30.

The system 10 is operable by a controller in the form of a computer (not shown) , the implementation of which is known in the art . Software loaded onto the computer operates the scrapper 24 to move a slice of the metal powder composition over pre-heater 38 and then onto the top surface of chamber 30. The scanner 34 then passes over the surface of the metal powder composition and causes the metal powder composition to sinter and form a metal. The laser 32 is operated in an on/off mode as the scanner 34 passes over the surface of the metal powder in chamber 30 according to, the desired metal part being built (metal part 36) . The operation of the laser 12 and the scanner 34 is controller by the computer with data stored within its software to automatically control the laser scanning and mechanical operation of the system 10.

An alternative exemplary device and method that could be used to direct laser sinter the metal powder composition of the disclosed embodiments is taught in US Patent No. 6,676,892, the disclosure of which is incorporated herein in its entirety.

Shrinkage & Dimensional accuracy

The dimensional accuracy of a sintered metal part is a very important issue in direct laser sintering process . The accuracy of the sintered parts is mainly determined by the shrinkage of the material and process parameters of the sintering machine and its associated control system.

Normally, high density and low shrinkage are difficult to achieved in the sintering process since the metal powders used in direct laser sintering are in the form of a "loose" powder that generally have an apparent density of 20-70%. Upon laser sintering, the metal powder composition undergoes densification and, in view of the low relative density, it would be expected that the densified material will undergo significant shrinkage.

Referring to Fig. 7, and without being bound by theory, there is shown a proposed schematic diagram model of expansion in plate caused by gravity in direct laser sintering for the metal powder composition of the disclosed embodiments. It has been found that the density of the metal powder can be enhanced by mixing the different sized metal powders .

In Fig. 7, shows a schematic diagram of a first metal powder (particle 1 and particle 2) , second metal powder (particle 3)and third metal powder (particle 4). The role of gravity is shown in Figure 7. The metal particle 3 falls down since metal particle 4 forms a liquid during direct laser sintering. The metal particle 3 pushes the metal particle 1 and 2. If the diameter of metal particle 3 is larger than the distance between metal particles 1 and 2, shrinkage in the height (X) direction and expansion "in plane" occurs (ie in plane is width (W) and length (L) direction; Fig. 7 only shows (X) and (W) ) . Accordingly, as the direct laser sintering process is a layer by layer process, the shrinkage in the X direction is compensated by the subsequently deposited metal powder layer that is sintered. This results in the sintered metal parts having a high volumetric shrinkage but low in-plane shrinkage (W and L) , resulting in the production of a highly dense and dimensionally accurate metal part. Accordingly, relative densities of more than 70% for copper metal parts have been obtained. More advantageously, relative densities of between 80-90% for copper metal parts have been obtained using direct laser sintering.

Experiment 1

10 kg of a metal powder composition capable of being sintered directly by a laser was prepared as follows:

5 kg of pure Cu powder (99.84% purity Cu) having a mean particle size of 70μm placed into a V-Cone blender (Powder 1) •

1 kg of pure Cu powder (99.84% purity Cu) having a mean particle size of 38μm was placed into the V-Cone blender (Powder 2) .

4 kg of a Cu₈gP₆Ag₅ powder was obtained by mixing 3.56 kg Cu powder, 0.24 Kg P and 0.2 kg Ag having a mean particle size of 38μm in a V-Cone blender (Powder 3) .

The Cu powders were obtained from Sulzer Metco (Singapore) Pte Ltd of Singapore.

Powders 1, 2 and 3 were blended in the V-Cone blender for 120 minutes to obtain a homogenous mixture. The composition of the metal powder is given in Table 2 below.

Table 2

The mixed metal powder composition was sintered directly in a laser using a High Temperature Laser Manufacturing System (HTLMS) that has been developed by the National University of Singapore. A full description of the HTLMS that was used in the experiment is disclosed in US Patent No. 6,621,039, which is incorporated in its entirety for reference .

The mixed metal powder composition was then subjected to laser sintering by the HTMLS using a laser operating at 200W, a scan speed of 240 mm/s, scan spacing of 0.2mm and a layer thickness of 0.075mm. The sintering occurred in an atmospheric atmosphere, that is in air where the oxygen content is about 21% by volume and the reminder being substantially nitrogen and any other gasses normally present in air.

Results of experiment 1

A sample of the powder 3 and pure Cu were subjected to Simultaneous Thermal Analysis (STA) using a Simultaneous Thermal Analyser. The results of the STA is shown in Fig. 2, which shows STA traces of powder 3 and pure Cu. The STA traces shown in Fig. 2 indicate that the melting point of powder 3 is 646°C and that of pure Cu is 1083 °C. No reactions occurred during heating.

A sample of the sintered metal produced in experiment 1 was obtained and the surface morphology of the sintered sample is shown in Fig. 3 under magnification. Bridges (refer to arrow 40.) between the particles are clearly visible, indicating that liquid forms and fills in between the pore space. The meniscus shape of the bridges is concave, suggesting good wetting between the two phases.

Referring to Fig. 4, there is shown a microstructure of the sintered sample of the composition prepared in example 1. Fig. 4 shows clear structural metal particles and surrounding binder, suggesting that the bonding mechanism is liquid phase sintering.

Fig. 5 shows a Scanning Electron Microscope (SEM) image of the sintered sample of the composition prepared in example 1. The image shows the interface of Cu particles from powders 1 and 2 and the powder 3 acting as a binder. The integrity of Cu grain boundary and the compact bonding between the Cu particles and the SCuP binder indicates good wetting between the particles.

Fig. 6(a) shows an X-ray pattern of the starting powder composition of example 1. Fig. 6(b) shows an X-ray pattern of the sintered sample . A comparison of the two X-Ray patterns indicates that no oxidization occurred during the sintering. The relative density of the metal produced in experiment 1 was found to be 74.3%.

Example 2 10 kg of a metal powder composition capable of being sintered directly by a laser was prepared as follows :

4 kg of pure Cu powder (99.84% purity Cu) having a mean particle size of 70μm placed into a V-Cone blender (Powder 1) .

2 kg of pure Cu powder (99.84% purity Cu) having a mean particle size of 38μm was placed into the V-Cone blender (Powder 2) .

4 kg of a Cu₈₉P₆Ag_s powder was obtained by mixing 3.56 kg Cu powder, 0.24 Kg P and 0.2 kg Ag having a mean particle size of 38μm (Powder 3) in a V-Cone blender.

Powders 1, 2 and 3 were mixed in a V-Cone blender for 120 minutes.

The relative density of the metal produced in experiment 2 was found to be 77.1%.

Comparative Example

10 kg of a comparative example 3 of a metal powder was prepared as follows:

6 kg of pure Cu powder (99.84% purity Cu) having a mean particle size of 70μm placed into a V-Cone blender (Powder 1) •

4 kg of a Cu₈₉P₆Ag_s powder was obtained by mixing 3.56 kg Cu powder, 0.24 Kg P and 0.2 kg Ag having a mean particle size of 38μm (Powder 3) in a V-Cone blender. Powders 1 and 3 were mixed in a V-Cone blender for 120 minutes .

The difference between the powder composition of Experiment 2 and that of the comparative example is that a second powder was not included in the composition. Both compositions were subjected to direct laser sintering using the HTMLS at the following operating parameters: fixed scan speed of 160mm/s, scan spacing of 0.2mm and layer thickness of 0.075mm.

Table 3 shows the shrinkage in scan direction (ie shrinking in plane) of the metal powder of the Comparative Example and that of Example 2.

Table 3

From this table, it can be seen that the composition of example 2 had less shrinkage than that of the comparative example .

Applications

The disclosed embodiments provide a metal powder composition that is capable of being sintered to produce a three-dimensional metal product that has a density of 70% or more.

The disclosed metal powder composition is capable of being sintered and used in the fabrication of metallic parts. Upon sintering the disclosed metal powder composition, the fabricated parts are shown to have high relative density and to have relatively minimal in-plane shrinkage or less shrinkage compared to that of known metal powder compositions .

The disclosed metal powder composition is capable of being sintered using a relatively low powered laser. The disclosed metal powder composition can be direct sintered using only the relatively low powered laser. Advantageously, the use of relatively a low powered laser reduces the cost of direct laser sintering compared to other methods that utilize high powered laser for sintering.

Advantageously, the method and system that utilizes the disclosed metal powder to produce metal products may automatically compensate for sintering shrinkage without sacrificing the product density.

The disclosed metal powder is also capable of being sintered under ambient atmospheric conditions . The disclosed metal powder is also capable of being sintered without any pre-heating.

It will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.

Claims

1. A metal powder composition comprising: a first metal powder comprising copper and having a first mean particle size; a second metal powder comprising copper and having a second mean particle size that is less than the first mean particle size; and a third metal powder capable of at least partially melting at a temperature that is lower than the melting temperatures of the first and second metal powders and having a third mean particle size less than the first and second mean particle sizes.

2. A metal powder composition as claimed in claim 1, comprising about 30% to about 70% by weight of the first metal powder.

3. A metal powder composition as claimed in claim 1 or claim 2, wherein the first metal powder has a mean particle size in the range between about 50μm to about 90μm.

4. A metal powder composition as claimed in any one of the preceding claims, comprising about 5% to about 20% by weight of the second metal powder.

5. A metal powder composition as claimed in any one of the preceding claims, wherein the second metal powder has a mean particle size in the range between about 25μm to about 45μm.

6. A metal powder composition as claimed in any one of the preceding claims, comprising about 10% to about 65% of the third metal powder.

7. A metal powder composition as claimed in any one of the preceding claims, wherein the third metal powder has a mean particle size in the range between about lμm to about 25μm.

8. A metal powder composition as claimed in any one of the preceding claims, wherein the ratio of the melting temperature of the first and second metal powders to the melting temperature of the third metal powder is about 3 or less .

9. A metal powder composition as claimed in any one of the preceding claims, wherein the copper of the first or second metal powders further comprise one or more metals to form a copper alloy.

10. A metal powder composition as claimed in claim 9, wherein the one or more metals are selected from the group consisting of: chromium, cobalt, lead, manganese, molybdenum, nickel, silver, tin, tungsten, zinc, and one or more mixtures thereof.

11. A metal powder composition as claimed in any one of the preceding claims, wherein the copper of the first or second metal powders further comprise one or more additives selected from the group consisting of: aluminum, beryllium, bismuth, cadmium, carbon, iron, magnesium, niobium, phosphorous, silicon, tantalum, vanadium, zirconium and one or more mixtures thereof .

12. A metal powder composition as claimed in any one of the preceding claims, wherein the amount of copper in the first and second metal powders may be in the range of about 30% to about 99% by weight.

13. A metal powder composition as claimed in any one of the preceding claims, wherein the third metal powder is a Cu alloy.

14. A metal powder composition as claimed in claim 13, wherein the copper alloy comprises Cu, Ag and P.

15. A metal powder composition as claimed claim 14, wherein the copper alloy comprises : about 2% to about 20% by weight Ag; about 5% to about 8% by weight P; and the remainder being Cu and any incidental impurities.

16. A method of preparing a metal powder composition, the method comprising the steps of: providing a first metal powder comprising Cu and having a first mean particle size,- providing a second metal powder comprising Cu and having a second mean particle size that is less than the first particle size; providing a third metal powder capable of at least partially melting at a temperature that is lower than the melting temperatures of the first and second metal powders and having a third mean particle size less than the first and second mean particle sizes; and combining the first metal powder, the second metal powder and the third metal powder to form the metal powder composition.

17. A sintered metal product prepared by sintering a metal powder composition, the metal powder composition comprising: a first metal powder comprising copper and having a first mean particle size; a second metal powder comprising copper and having a second mean particle size that is less than the first particle size; and a third metal powder capable of at least partially melting at a temperature that is lower than the melting temperatures of the first and second metal powders and having a third mean particle size less than the first and second mean particle sizes.

18. A sintering method comprising: sintering a metal powder composition comprising: a first metal powder comprising copper and having a first mean particle size; a second metal powder comprising copper and having a second mean particle size that is less than the first particle size; and a third metal powder capable of at least partially melting at a temperature that is lower than the melting temperatures of the first and second metal powders and having a third mean particle size less than the first and second mean particle sizes to provide a sintered metal product .

19. A sintering method as claimed in claim 18, wherein the sintering step comprises directing laser energy at a target surface of the metal powder composition.

20. A sintering method as claimed in claim 19, further comprising depositing a layer of the metal powder onto the target surface.

21. A sintering method as claimed in claim 18 or claim 19, wherein the sintering occurs at an absolute pressure in the range between 70 kPa to 120 kPa.

22. A sintering method as claimed in anyone of claims 18 to 21, wherein the sintering occurs at a temperature in the range of 600°C to 1200°C.

23. A sintering method as claimed in anyone of claims 18 to 22, wherein the gas surrounding the metal power composition is substantially that of air.

24. A sintered metal product produced according to the method according to any one of claims 18 to 23.

25. Use of a metal powder composition in a sintering process, the metal powder composition comprising: a first metal powder comprising copper and having a first mean particle size; a second metal powder comprising copper and having a second mean particle size that is less than the first particle size; and a third metal powder capable of at least partially melting at a temperature that is lower than the melting temperatures of the first and second metal powders and having a third mean particle size less than the first and second mean particle sizes.

26. A metal powder composition, substantially as herein described with reference to example 1 or example 2.

27. A method of preparing a metal powder composition, substantially as herein described with reference to example 1 or example 2.