CA2770464A1 - A process for producing a metal-matrix composite of significant .delta.cte between the hard base-metal and the soft matrix - Google Patents
A process for producing a metal-matrix composite of significant .delta.cte between the hard base-metal and the soft matrix Download PDFInfo
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- CA2770464A1 CA2770464A1 CA2770464A CA2770464A CA2770464A1 CA 2770464 A1 CA2770464 A1 CA 2770464A1 CA 2770464 A CA2770464 A CA 2770464A CA 2770464 A CA2770464 A CA 2770464A CA 2770464 A1 CA2770464 A1 CA 2770464A1
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C27/00—Alloys based on rhenium or a refractory metal not mentioned in groups C22C14/00 or C22C16/00
- C22C27/04—Alloys based on tungsten or molybdenum
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/10—Metallic powder containing lubricating or binding agents; Metallic powder containing organic material
- B22F1/105—Metallic powder containing lubricating or binding agents; Metallic powder containing organic material containing inorganic lubricating or binding agents, e.g. metal salts
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/17—Metallic particles coated with metal
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
- B22F3/12—Both compacting and sintering
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C47/00—Making alloys containing metallic or non-metallic fibres or filaments
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C9/00—Alloys based on copper
- C22C9/02—Alloys based on copper with tin as the next major constituent
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F9/00—Making metallic powder or suspensions thereof
- B22F9/02—Making metallic powder or suspensions thereof using physical processes
- B22F9/04—Making metallic powder or suspensions thereof using physical processes starting from solid material, e.g. by crushing, grinding or milling
- B22F2009/042—Making metallic powder or suspensions thereof using physical processes starting from solid material, e.g. by crushing, grinding or milling using a particular milling fluid
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
- B22F2998/10—Processes characterised by the sequence of their steps
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F2999/00—Aspects linked to processes or compositions used in powder metallurgy
Abstract
The present invention relates to a process for producing a metal-matrix composite of significant ?CTE between the hard base-metal and the soft matrix. The process includes the steps of sintering, pressing and enforced infiltration of the metal-matrix composite compact acting wherein the process is driven by differential thermal expansion coefficients between shell and core materials.
Description
A PROCESS FOR PRODUCING A METAL-MATRIX COMPOSITE OF SIGNIFICANT
LCTE BETWEEN THE HARD BASE-METAL AND THE SOFT MATRIX
FIELD OF INVENTION
The present invention relates to a process for producing a metal-matrix composite of significant ACTE between the hard base-metal and the soft matrix.
BACKGROUND ART
Recently metal matrix composites (MMCs) have received much attention due to their electrical and mechanical properties. Tungsten composite (W-bronze and W-Cu) is an example of MMC's materials that has gained great importance in many applications.
Characterized by its high density, high strength, adequate fracture toughness, hardness, high wear resistance and low thermal expansion, make it very a good candidate as lead replacement materials in many military and industrial applications.
They are suitable for fabrication of ammunition, center of gravity (CG) adjusters, gyroscope rotors and radiation shelters. Other applications are irrelevant to lead replacement like kinetic energy penetrators and jet vanes. Additionally for W-Cu composites and due to their excellent thermal conductivity, they found their way to various electrical and electronic applications, these include, electrical contacts, resistance welding electrodes, electro-discharge machining electrodes, heat sinkers and power packaging for microelectronic and optoelectronics applications.
Alloying of W with bronze alloy is difficult to cast. Consulting W-Cu equilibrium phase diagram shows that W metal and Cu are almost completely immiscible in both solid and liquid phase. Cu heat of mixing with W is positive i.e.35.5kJ/mole. Energy of formation of W-Sn solid solution is positive as well i.e. 20kJ/mole..
Accordingly attaining fully dense sintered compacts of these systems is not easy to handle. To tackle this problem the researchers in the recent three decades tried different techniques and approaches. These techniques comprise liquid phase sintering, sintering at higher temperatures, using finer elemental powders and incorporating sintering activators (Fe, Co, Ni and Pd). Other more sophisticated technique is to change the surface morphology and the wettability of the W-base metal by thin film Ni coatings on the W
particles prior to sintering and mechanical alloying (MA) of the W composite elemental powders to reduce the W-W spacing and to mechanically super induce inter diffusion.
layer on the elemental powders.
So far all these techniques were not sufficient to attain fully dense net shape compacts out of these composite systems. Despite the success of all these approaches and techniques, they bring along negative impacts to at least one or two of the physical and mechanical properties of the sintered compacts like. conductivity, thermal expansion and strength. Another method and the most widely used are to infiltrate the sintered and porous W skeleton preforms by the matrix melt (bronze or copper).
The object of all these processes is to achieve homogeneous pore free MMC material with even distribution of the Cu. or bronze phase in the W composite structure.
Porosity is deleterious to flexural strength, electrical and thermal conductivity of the composite.
The pores and voids act as points of stress concentrations and reduce the cross-sectional area across which a load is applied and lead to a tremendous fall of the flexural strength. Air that is present in the pores has poor thermal and electrical conductivity and thus it deteriorates the overall thermal and electrical properties of the composite. Therefore, it is essential to avoid pores formation in the composite during its manufacturing process. Currently there are many infiltration techniques available for producing metal or metal-ceramics composite materials in particular tungsten-copper or tungsten-bronze composites.
The main steps of any conventional infiltration process are as follow.
= Tungsten powder preparation with average size of 1-5 m.
=. Optional step: coating the powder with nickel. Total nickel content is about0.04%.
= Mixing the tungsten powder with a polymer binder.
= Compacting the powder by a modeling method (metal injection molding, die pressing, isostatic pressing). Compaction should provide the predetermined porosity level (apparent density) of the tungsten structure.
= Solvent debinding.
= Sintering the green compact at 1200 C-1300 C in hydrogen atmosphere for 2hrs.
= Placing the sintered part on copper plate in the infiltration/sintering furnace.
= Infiltration of the sintered tungsten skeleton porous structure with copper at 1110 -1260 C in either hydrogen atmosphere or vacuum for 1 hour.
Infiltration of the sintered tungsten skeleton porous structure by the second metal, having a lower melting point, can be conducted under gas pressure (gas pressure infiltration), under the pressure of mold movable part i.e. ramming (squeeze casting infiltration) and under the die pressure (pressure die casting).
US Patent No 5963773 disclosed a method of fabricating tungsten skeleton structure comprising the step of forming a source powder by coating a tungsten powder with nickel Then admixing the source powder and a polymer binder, performing powder injection molding and obtaining a tungsten skeleton structure by removing the polymer binder. A copper plate is then placed beneath the tungsten skeleton structure and infiltration is carried out at temperature between 11502C andl2509C. This method is not viable for producing. complicated shapes.
US. Patent No. 5413751 describes a process for forming heat sinks and other heat dissipating elements by press-forming composite powders for metal components, for example tungsten and copper, to form pressed compacts and then sintering the pressed compacts to achieve a homogenous distribution of the copper throughout the tungsten-copper structure.
US Patents No. 4942076, 4988386, 5563101, disclose procedures of improving heat sink properties of W-Cu composite material utilized in microwave devices by maintaining even dispersion of tungsten particles having low thermal expansion coefficient within a copper matrix having high thermal conductivity. This process improves the thermal conductivity of the W-Cu composite and modifies the thermal expansion coefficient to be correspondent to that of Gallium Arsenide (Ga.
As.) Substrate utilized in microwave devices.
In fact almost all previous infiltration techniques utilized so far to infiltrate the W porous structure preforms, have been yielding composite structures which more or less have some weak points in their mechanical, electrical and micro structural properties. These points can be summarized as follow.
= The percentage of the infiltrated component cannot be easily controlled through infiltration process and going for higher infiltrant percentages is difficult.
= Liquid copper is known to have high, contact angles with several oxides which impede the infiltration process and accordingly control of furnace atmosphere is very essential for successful infiltration process.
= In the thermal debinding cycle of the tungsten green compact to produce porous 5 tungsten structure preform, formation of tungsten oxide (WO3) is very common.
This oxide is known to be very volatile and hence it is very important that it, is to be avoided to prevent material loss.
= For optimum and maximum infiltration, specific pore length and pore diameter (UD) are recommended and maintaining these recommendations in the tungsten porous preform is not easy.
= Mismatch between W skeleton and the matrix increases resistivity and deteriorates electrical specifications = Lakes of matrix solidified melts within the W skeleton lead. to non consistent mechanical properties.
.
LCTE BETWEEN THE HARD BASE-METAL AND THE SOFT MATRIX
FIELD OF INVENTION
The present invention relates to a process for producing a metal-matrix composite of significant ACTE between the hard base-metal and the soft matrix.
BACKGROUND ART
Recently metal matrix composites (MMCs) have received much attention due to their electrical and mechanical properties. Tungsten composite (W-bronze and W-Cu) is an example of MMC's materials that has gained great importance in many applications.
Characterized by its high density, high strength, adequate fracture toughness, hardness, high wear resistance and low thermal expansion, make it very a good candidate as lead replacement materials in many military and industrial applications.
They are suitable for fabrication of ammunition, center of gravity (CG) adjusters, gyroscope rotors and radiation shelters. Other applications are irrelevant to lead replacement like kinetic energy penetrators and jet vanes. Additionally for W-Cu composites and due to their excellent thermal conductivity, they found their way to various electrical and electronic applications, these include, electrical contacts, resistance welding electrodes, electro-discharge machining electrodes, heat sinkers and power packaging for microelectronic and optoelectronics applications.
Alloying of W with bronze alloy is difficult to cast. Consulting W-Cu equilibrium phase diagram shows that W metal and Cu are almost completely immiscible in both solid and liquid phase. Cu heat of mixing with W is positive i.e.35.5kJ/mole. Energy of formation of W-Sn solid solution is positive as well i.e. 20kJ/mole..
Accordingly attaining fully dense sintered compacts of these systems is not easy to handle. To tackle this problem the researchers in the recent three decades tried different techniques and approaches. These techniques comprise liquid phase sintering, sintering at higher temperatures, using finer elemental powders and incorporating sintering activators (Fe, Co, Ni and Pd). Other more sophisticated technique is to change the surface morphology and the wettability of the W-base metal by thin film Ni coatings on the W
particles prior to sintering and mechanical alloying (MA) of the W composite elemental powders to reduce the W-W spacing and to mechanically super induce inter diffusion.
layer on the elemental powders.
So far all these techniques were not sufficient to attain fully dense net shape compacts out of these composite systems. Despite the success of all these approaches and techniques, they bring along negative impacts to at least one or two of the physical and mechanical properties of the sintered compacts like. conductivity, thermal expansion and strength. Another method and the most widely used are to infiltrate the sintered and porous W skeleton preforms by the matrix melt (bronze or copper).
The object of all these processes is to achieve homogeneous pore free MMC material with even distribution of the Cu. or bronze phase in the W composite structure.
Porosity is deleterious to flexural strength, electrical and thermal conductivity of the composite.
The pores and voids act as points of stress concentrations and reduce the cross-sectional area across which a load is applied and lead to a tremendous fall of the flexural strength. Air that is present in the pores has poor thermal and electrical conductivity and thus it deteriorates the overall thermal and electrical properties of the composite. Therefore, it is essential to avoid pores formation in the composite during its manufacturing process. Currently there are many infiltration techniques available for producing metal or metal-ceramics composite materials in particular tungsten-copper or tungsten-bronze composites.
The main steps of any conventional infiltration process are as follow.
= Tungsten powder preparation with average size of 1-5 m.
=. Optional step: coating the powder with nickel. Total nickel content is about0.04%.
= Mixing the tungsten powder with a polymer binder.
= Compacting the powder by a modeling method (metal injection molding, die pressing, isostatic pressing). Compaction should provide the predetermined porosity level (apparent density) of the tungsten structure.
= Solvent debinding.
= Sintering the green compact at 1200 C-1300 C in hydrogen atmosphere for 2hrs.
= Placing the sintered part on copper plate in the infiltration/sintering furnace.
= Infiltration of the sintered tungsten skeleton porous structure with copper at 1110 -1260 C in either hydrogen atmosphere or vacuum for 1 hour.
Infiltration of the sintered tungsten skeleton porous structure by the second metal, having a lower melting point, can be conducted under gas pressure (gas pressure infiltration), under the pressure of mold movable part i.e. ramming (squeeze casting infiltration) and under the die pressure (pressure die casting).
US Patent No 5963773 disclosed a method of fabricating tungsten skeleton structure comprising the step of forming a source powder by coating a tungsten powder with nickel Then admixing the source powder and a polymer binder, performing powder injection molding and obtaining a tungsten skeleton structure by removing the polymer binder. A copper plate is then placed beneath the tungsten skeleton structure and infiltration is carried out at temperature between 11502C andl2509C. This method is not viable for producing. complicated shapes.
US. Patent No. 5413751 describes a process for forming heat sinks and other heat dissipating elements by press-forming composite powders for metal components, for example tungsten and copper, to form pressed compacts and then sintering the pressed compacts to achieve a homogenous distribution of the copper throughout the tungsten-copper structure.
US Patents No. 4942076, 4988386, 5563101, disclose procedures of improving heat sink properties of W-Cu composite material utilized in microwave devices by maintaining even dispersion of tungsten particles having low thermal expansion coefficient within a copper matrix having high thermal conductivity. This process improves the thermal conductivity of the W-Cu composite and modifies the thermal expansion coefficient to be correspondent to that of Gallium Arsenide (Ga.
As.) Substrate utilized in microwave devices.
In fact almost all previous infiltration techniques utilized so far to infiltrate the W porous structure preforms, have been yielding composite structures which more or less have some weak points in their mechanical, electrical and micro structural properties. These points can be summarized as follow.
= The percentage of the infiltrated component cannot be easily controlled through infiltration process and going for higher infiltrant percentages is difficult.
= Liquid copper is known to have high, contact angles with several oxides which impede the infiltration process and accordingly control of furnace atmosphere is very essential for successful infiltration process.
= In the thermal debinding cycle of the tungsten green compact to produce porous 5 tungsten structure preform, formation of tungsten oxide (WO3) is very common.
This oxide is known to be very volatile and hence it is very important that it, is to be avoided to prevent material loss.
= For optimum and maximum infiltration, specific pore length and pore diameter (UD) are recommended and maintaining these recommendations in the tungsten porous preform is not easy.
= Mismatch between W skeleton and the matrix increases resistivity and deteriorates electrical specifications = Lakes of matrix solidified melts within the W skeleton lead. to non consistent mechanical properties.
.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides a process for producing a metal-matrix composite of significant ACTE between the hard base-material and any element type of the soft metal matrix. The process includes the steps of sintering, pressing and enforced infiltration of the sintered compact wherein the process is driven by differential thermal expansion coefficients between the shell and the core materials.
The present invention consists of several novel features and a combination of parts hereinafter fully described and illustrated in the accompanying description and drawings, it being understood that various changes in the details may be made without departing from the scope of the invention or sacrificing any of the advantages of the present invention.
Accordingly, the present invention provides a process for producing a metal-matrix composite of significant ACTE between the hard base-material and any element type of the soft metal matrix. The process includes the steps of sintering, pressing and enforced infiltration of the sintered compact wherein the process is driven by differential thermal expansion coefficients between the shell and the core materials.
The present invention consists of several novel features and a combination of parts hereinafter fully described and illustrated in the accompanying description and drawings, it being understood that various changes in the details may be made without departing from the scope of the invention or sacrificing any of the advantages of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be fully understood from the detailed description given herein below and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, wherein:
Fig. 1 is a schematic representation of the process for producing a metal-matrix composite of significant zCTE between the hard base-metal and the soft,.
matrix according to the preferred embodiments of the present invention;
Fig. 2 is a 3D schematic diagram of the process of the present invention;
Fig. 3 (a) is an optical graph of W80wt.%-Cu18-Sn shell-on-core sintered compact cross section of as received elemental powder, the shell is bronze admix. The compact sintered at 1150 C for 3 hours under H2/N2 20/80 wt. ratio as protective gas utilizing the process of the present invention.
Fig. 3 (b) is an optical graph of shell-on-core sintered compact cross section of W50wt.%-Cu45-Sn sintered compact of two-steps ball milled powder. The shell is copper wherein the compact is sintered at 1150 C for 3 hours under H2/N2 20/80 wt.
ratio as protective gas utilizing the process of the present invention;
Fig. 3 (c) is an optical graph of shell-on-core sintered compact cross section of W80wt.%-Cu18-Sn sintered compact. The compact is sintered at 1150 C for 3 hours under H2/N2 20/80 wt. ratio as protective gas utilizing the process of the present invention Fig. 3 (d) is an optical graph shell-on-core sintered compact cross section of W40wt%-pre-alloyed bronze sintered compact. The compact is. sintered at 1150 C for 3 hours under. H2/N2 20/80 wt ratio protective gas utilizing the process of the present invention;
Fig. 4 is the micro hardness profile across the solidified Cu-Sn shell and the W80wt.%-Cu18-Sn sintered compact of 99% of its theoretical density.
Fig. 5 shows SEM micrographs of W 80wt.%-Cu18-Sn sintered compacts of as received elemental powder sintered and densified by this invention, The last micrograph represents sintered compact of similar composition sintered by the conventional method of uniaxial compaction and sintering.
Fig. 6 (a) shows the optical micrographs of W80wt.%-Cu18-Sn compacts of as-received powder sintered conventionally at 1150 C for 3 hours;
Fig. 6 (b) shows the optical micrographs of W80wt.%-Cu18-Sn compacts of as-received powder sintered by the process of the present invention under similar sintering conditions as in Fig. 6 (a).
Fig. 6 (c) shows the optical micrographs of W90wt.%-Cu18-Sn compacts of as-received elemental powder sintered conventionally at 1150 C for 3 hours.
Fig. 6 (d) shows the optical micrographs of W90wt.%-Cu18-Sn compacts of similar composition to Fig. 6 (c) sintered by the process of the present invention under similar sintering conditions as in Fig. 6 (c).
The present invention will be fully understood from the detailed description given herein below and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, wherein:
Fig. 1 is a schematic representation of the process for producing a metal-matrix composite of significant zCTE between the hard base-metal and the soft,.
matrix according to the preferred embodiments of the present invention;
Fig. 2 is a 3D schematic diagram of the process of the present invention;
Fig. 3 (a) is an optical graph of W80wt.%-Cu18-Sn shell-on-core sintered compact cross section of as received elemental powder, the shell is bronze admix. The compact sintered at 1150 C for 3 hours under H2/N2 20/80 wt. ratio as protective gas utilizing the process of the present invention.
Fig. 3 (b) is an optical graph of shell-on-core sintered compact cross section of W50wt.%-Cu45-Sn sintered compact of two-steps ball milled powder. The shell is copper wherein the compact is sintered at 1150 C for 3 hours under H2/N2 20/80 wt.
ratio as protective gas utilizing the process of the present invention;
Fig. 3 (c) is an optical graph of shell-on-core sintered compact cross section of W80wt.%-Cu18-Sn sintered compact. The compact is sintered at 1150 C for 3 hours under H2/N2 20/80 wt. ratio as protective gas utilizing the process of the present invention Fig. 3 (d) is an optical graph shell-on-core sintered compact cross section of W40wt%-pre-alloyed bronze sintered compact. The compact is. sintered at 1150 C for 3 hours under. H2/N2 20/80 wt ratio protective gas utilizing the process of the present invention;
Fig. 4 is the micro hardness profile across the solidified Cu-Sn shell and the W80wt.%-Cu18-Sn sintered compact of 99% of its theoretical density.
Fig. 5 shows SEM micrographs of W 80wt.%-Cu18-Sn sintered compacts of as received elemental powder sintered and densified by this invention, The last micrograph represents sintered compact of similar composition sintered by the conventional method of uniaxial compaction and sintering.
Fig. 6 (a) shows the optical micrographs of W80wt.%-Cu18-Sn compacts of as-received powder sintered conventionally at 1150 C for 3 hours;
Fig. 6 (b) shows the optical micrographs of W80wt.%-Cu18-Sn compacts of as-received powder sintered by the process of the present invention under similar sintering conditions as in Fig. 6 (a).
Fig. 6 (c) shows the optical micrographs of W90wt.%-Cu18-Sn compacts of as-received elemental powder sintered conventionally at 1150 C for 3 hours.
Fig. 6 (d) shows the optical micrographs of W90wt.%-Cu18-Sn compacts of similar composition to Fig. 6 (c) sintered by the process of the present invention under similar sintering conditions as in Fig. 6 (c).
Fig. 7 shows a schematic representation of the process of the present invention at its final stage.
Fig. 8 (a) shows a SEM micrograph of W50wt.%-pre-alloy bronze compact of ball milled powder sintered conventionally.
Fig. 8 (b) shows a SEM micrograph of W50wt.%-pre-alloy bronze compact of ball milled powder sintered by the present invention wherein sintered density of 99%
theoretical density is achieved.
Fig. 8 (c) shows a SEM micrograph of W50wt.%-Cu45-Sn compact of two-step ball milled powder sintered conventionally.
Fig. 8 (d) shows a SEM micrograph of W50wt.%-Cu45-Sn compact of two-step ball milled powder sintered by the present invention technique wherein sintered density of 98% theoretical density is achieved.
Fig. 9 (a) shows the EDX line scan across the shell/core boarder of W50wt%-Cu45-Sn sintered compact of ball milled powder sintered by the process of the present invention.
Fig. 9 (b) shows the EDX line scan of sintered compact of similar composition of W50wt%-Cu45-Sn sintered compact of ball milled powder sintered by the present invention technique but with pre-alloy bronze matrix. The shell is of Cu element.
Fig. 10 shows the alumina ceramics mould shows the cavity in where the W-bronze green compact placed and covered all around by the Cu-Sn powder mix shell before sintering.
5 Fig. 11 shows a typical thermal and infiltration sintering cycle program of the present invention wherein the sintering, heating and cooling temperature rates can be altered according to the sintered material specifications.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention relates to a process for producing a metal-matrix composite of significant ACTE between the hard base-metal and the soft matrix. Hereinafter, this specification will describe the present invention according to the preferred embodiments of the present invention. However, it is to be understood that limiting the description to the preferred embodiments of the invention is merely to facilitate discussion of the present invention and it is envisioned that those skilled in the art may devise various modifications and equivalents without departing from the, scope of the appended claims.
The present invention is generally related to a method for producing a composite material comprising a matrix phase and a dispersed phase, in particular metal-metal, metal-ceramics/carbide or composite material, such as tungsten-bronze, tungsten-copper, AI-SiC and Al-AI203. The hard base component could be particulates, dispersoids, cermets, short or continuous fibers, monofilament or whiskers reinforcements of any material type having significantly lower CTE value than that of the matrix. The process includes hot pressing, sintering and infiltration, acting simultaneously in one stage to yield microstructure of even distribution of the dispersed phase in the metal matrix.
The "three in one densification process" relates to the sintering/infiltration of metal-metal or metal-ceramics/carbide composite material by one process comprises sintering, hot pressing and enforced infiltration acting simultaneously in one step. The objective of this invention is to produce, pore free, homogeneous sintered compact structure with minimum defects at its near theoretical density. The hard metal or ceramics reinforcements uniformly distributed in a softer metal matrix. The first stage is the preparation of the as received composite powder components, either by mixing or ball milling. Usually the composite consists of two or more components, i.e.
the hard base metal component of higher melting point like tungsten and the matrix soft component having lower melting point, like bronze or copper. The powders mixture consist of W base metal ranges between 50-90 wt percent and the balance. is pre alloyed bronze or admixture of Cu-SnlOwt%. The ball milled and the as-received admixed powders are die-pressed separately under uniaxial pressure ranges between 360-720 MPa preferably around 400 MPa to yield compact discs of 13mm diameter and around 4 mm thickness. In case of utilizing the as received hard pre-alloyed bronze powder as the compact soft component i.e.. the matrix, it is necessary to add 0.01 of zinc stearate as a binder to enhance the green compaction process, while it is not important to add any sort of binder if the compact soft component is Cu or Cu-Sn10wt% admixture. The green compact is then placed in a ceramic mold of suitable cavity, large enough to accommodate the green compact and then covered all around by Cu or bronze powder called here as the outer shell. In case of green compact being fabricated from ball milled and mechanically alloyed powders, the outer covering shell should be a single phase elemental powder; otherwise the sintered, compact suffers severe swelling induced by the divergency in diffusion pathways and powder particle size between the core and the covering shell. The composite system i.e. the green compact as a core and the covering shell is then sintered in a furnace following a pre designed sintering program comprises heating up stage at heating rate of 5-8 C/min and isothermal sintering stage at a temperature of 1150 C- 1300 C for 2-3 hours. The final stage is the cooling down stage. It is essential to pay great attention to the cooling down rate. Usually 4-8 C/min is suitable for the W composite system.
Hereinafter the detailed description of the invention will be described in accordance with the accompanying drawings which will be referred either individually or collectively, in any combination thereof, wherein:
Fig. 1 is a schematic representation of the process for producing a metal-matrix composite of significant ACTE between the hard base-metal and the soft matrix according to the preferred embodiments of the present invention. This figure.
shows that the process which is a "three in one densification process" on its ongoing action.
As the skin of the outer shell starts to solidify and as the solidification process proceeds the outer shell shrinks and compresses continuously towards the center, the compression stress builds up gradually driven by the differential thermal expansion coefficients ACTE of the shell and the compact materials at the core.
Fig. 2 shows a 3D schematic diagram of the present invention technique wherein the core is representing the W-Cu-Sn compact encircled or surrounded by Cu-Sn shell. As the shell solidifies, it shrinks and exerts compression stress on the core which enhances the core densification process.
Fig. 3 (a) shows an optical graph of W80wt.%-Cu18-Sn shell-on-core sintered compact cross section of as received elemental powder, the shell is bronze admix. The compact sintered at 1150 C for 3 hours under H2/N2 20/80 wt. ratio as protective gas utilizing the process of the present invention.
Fig. 3 (b) shows an optical graph of shell-on-core sintered compact cross section of W50wt.%-Cu45-Sn sintered compact of two-steps ball milled powder. The shell.
is copper wherein the compact is sintered at 1150 C for 3 hours under H2/N2 20/80 wt.
ratio as protective gas utilizing the process of the present invention;
Fig. 3 (c) shows an optical graph of shell-on-core sintered compact cross section of W80wt.%-Cu18-Sn sintered compact. The compact is sintered at 1150 C for 3 hours under H2/N2 20/80 wt. ratio as protective gas utilizing the process of the present invention Fig. 3 (d) shows an optical graph shell-on-core sintered compact cross section of W40wt%-pre-alloyed bronze sintered compact. The compact is sintered at 1150 C
for 3 hours under H2/N2 20/80 wt ratio protective gas utilizing the process of the present invention Fig. 4 shows the micro hardness profile across. the solidified Cu-Sn shell and the W80wt.%-Cu18-Sn sintered compact of 99% of its theoretical density.
Fig. 5 shows the SEM micrographs of W 80wt.%-Cu18-Sn sintered compacts of as received elemental powder densified by the process, in which hot pressing, sintering and infiltration process acting together. The micrographs reveal sintered compacts having 99% theoretical density. The last micrograph represents sintered compact of similar composition sintered by the conventional method of uniaxial compaction and sintering.
Fig. 6 (a) shows the optical micrographs of W80wt.%-Cu18-Sn compacts of as-received powder sintered conventionally at 1150 C for 3 hours;
Fig. 6 (b) shows the optical micrographs of W80wt.%-Cu18-Sn compacts of as-received powder sintered by the process of the present invention under similar sintering conditions as in Fig. 6 (a).
5 Fig. 6 (c) shows the optical micrographs of W90wt.%-Cu18-Sn compacts of as-received elemental powder sintered conventionally at 1150 C for 3 hours.
Fig. 6 (d) shows the optical micrographs of W90wt.%-Cu18-Sn compacts of similar composition to Fig. 6 (c) sintered by the process of the present invention under similar 10 sintering conditions as in Fig. 6 (c).
Fig. 7 shows a schematic representation of the process of the present invention at its final stage. As the sintering process elapsed and the covering shell melt cools down and gradually solidifies, it undergoes a substantial contraction driven by its high 15 thermal expansion coefficient and step by step it commences compressing and tightening firmly the core which has less thermal expansion coefficient and less contraction. This action is hot-isostatic-pressing-like action and leads to denser sintered compacts of near its theoretical density.
Fig. 8 (a) shows a SEM micrograph of W50wt.%-pre-alloy bronze compact of ball milled powder sintered conventionally.
Fig. 8 (b) shows a SEM micrograph of W50wt.%-pre-alloy bronze compact of ball milled powder sintered by the present invention wherein sintered density of 99%
theoretical density is achieved.
Fig. 8 (c) shows a SEM micrograph of W50wt.%-Cu45-Sn compact of two-step ball milled powder sintered conventionally.
Fig. 8 (d) shows a SEM micrograph of W50wt.%-Cu45-Sn compact of two-step ball milled powder sintered by the present invention technique wherein sintered density of 98% theoretical density is achieved.
Fig. 9 (a) shows the EDX line scan across the shell/core boarder of W50wt%-Cu45-Sn sintered compact of ball milled powder sintered by the process of the present invention..
Fig. 9 (b) shows the EDX line scan of sintered compact of . similar composition of W50wt%-Cu45-Sn sintered compact of ball milled powder sintered by the present invention technique but with pre-alloy bronze matrix. The shell is of Cu element.
Fig. 10 shows the alumina ceramics mould shows the cavity in where the W-bronze green compact placed and covered all around.by the Cu-Sn powder mix shell before sintering.
Fig. 11 shows a typical thermal and infiltration sintering cycle program of the present invention wherein the sintering, heating and cooling temperature rates can be altered according to the sintered material specifications.
So far, the most widely used method to attain fully dense W-bronze or W-Cu composite compacts, is to infiltrate pre sintered, porous W-base metal preforms by bronze or Cu melts. This technique proves to be costly and time consuming as it comprises many stages. In this investigation, manipulation the powder constituent physical properties of W composites has led to the implementation of exclusively novel "three in one densification invention" process includes sintering, in-situ hot isostatic pressing (HIP) and infiltration acting simultaneously at relatively low densification temperature of 1150 C under H2/N2 20/80 wt. ratio as protective gas. Pilot sintered/infiltrated compacts of = 99% theoretical density of different W (50, 80 and 90) wt.% balance is Cu-10wt.%Sn compacts of as received W, Cu and Sri metal powder precursors were produced. Other. sintered/infiltrated compact sets of W50wt.%
and W80wt.%, balance is bronze 10wt.%Sn compacts of ball milled powder mixes gave sintered density 95% of theoretical density. The compacts were subjected to density measurements, shrinkage and porosity characterization. Microstructure, hardness and densification mechanisms of the sintered/infiltrated compacts were evaluated and examined using scanning electron microscopy (SEM), energy dispersive x-ray analysis (EDX) and x-ray diffraction analysis (XRD).
During the heating up stage and the isothermal stage, sintering of the compact at the core is proceeding. The main sintering mechanisms at those two stages are,.
firstly by solid state diffusion and as the liquid phase forms particles rearrangement becomes the dominant sintering mechanism. As the temperature exceeds the shell's powder melting temperature, the powder starts to melt and wet the compact surfaces which now become a concentric core within the covering shell and forming the so called shell-core system. The melted covering shell usually assumes spherical shape under its surface tension. At this stage, the melted. shell enhances the sintering process of the core. It improves core protection from furnace environment, reduces oxidation and prevents contamination. As the heating-up stage and the isothermal stage are elapsed. The melted shell cools down and eventually starts to solidify. The solidification process proceeds gradually from the outside towards the center.
Now if the density of the solidified shell is greater than that of its liquid, the new solidified thin shell will occupies less volume than the original liquid from which it solidifies;
accordingly negative internal pressure builds up in the not-yet-solidified metal melt around the core. The magnitude of this negative internal pressure depends on the cooling rate, the solidified sphere diameter and its material physical properties (CTE of metal, metal thermal conductivity and the ratio of solid/liquid density). As far as this internal negative pressure is not counter balanced by an external force or by outer sphere surface buckling, it will experience vacuum-sintering-like effects and leads to the elimination of some voids and porosities from the core. As the solidification of the outer shell terminates, it undergoes a substantial thermal contraction due to its high CTE and starts compressing firmly and.isostaticly the compact at the core which is not solidified yet, firstly because of the heat transfer sequence and secondly because it contains tungsten particles having low heat dissipation rate and act as a thermal source. At this stage the strength modulus of the solidified covering shell is substantially higher than that of the not-yet-solidified soft component (mushy matrix) within the compact at the core. The tensile strength of bronzel0%Sn is temperature dependant. As the temperature increases from room temperature to 3009Cthe bronze metal looses around 80% of its original ultimate tensile strength.
Accordingly, the matrix component of lower strength within the core, yields under the applied external isostatic pressure and bring the W particles together and expel all voids and residual porosities out to the compact/covering shell interface leaving high dense sintered core.
The sintered compact i.e. the core remains under compressive stress even after its own matrix entirely turns to solid and its temperature reaches room temperature.
The main features of the "three in one densification invention" are.
= It is very simple and cost effective.
The weight percentages of the sintered compact components can be preliminary controlled. It is easy to increase the matrix weight percentage of the compact which is important in improving the thermal conductivity of the product.
= No need for any sort of sintering additives which can lead to non controllable shrinkage during liquid phase sintering and have negative effects on thermal conductivity of the sintered part.
= The covering shell shields the composite compact during sintering process and prevents compact oxidation and contamination.
= Post sintering/infiltration process, it is easy to salvage the outer shell machined metal for the next production batch usages.
An aspect of the present invention specifies a method for producing a composite material having matrix and dispesoid phase like W-bronze, where W is the dispesoid phase and the bronze is the matrix. The method comprises die pressing of the composite elemental powders to yield a green compact and then to place this compact.
in a ceramics mold of suitable cavity. The green compact is adjusted and placed in the cavity as a concentric core surrounded by the covering shell powder. The weight of the loose covering shell powder encircled the green compact is at least equal to its weight.
The ceramics mold and its charge are then introduced into a furnace and the green compact with the covering shell powder sinter at temperature above the shell powder melting temperature for a certain time under protective gas, hydrogen or inert gas to prevent oxidation. The compact soft component metal, called here the matrix, is usually similar to the covering shell metal unless specified otherwise. Now as the core i.e. the composite green compact gets sintered and as the temperature exceeds the 25. matrix melting temperature the liquid phase forms inside and outside the core and enhance the densification process. When the isothermal sintering stage entirely elapsed, the charge starts to cool down. The differential thermal expansion between the core material and the covering shell material leads to a different degree of contraction depending on their materials thermal expansion coefficients. At certain stage, the completely solidified shell starts contracting and exerting isostatic pressure 5 on the semi solidified core. This induced pressure and stress/strain reaches its maximum degree as the temperature drops to room temperature. The amount of the exerted stress/strain on the sintered compact at the core depends on the temperature gradient, the volume fraction of the W hard component owing .to the lower thermal expansion coefficient and the bulk volume of the core and that of the outer shell. The 10 coefficients of thermal expansion (commonly referred to as iCTE) of the W-bronze core are.
a`= VIb 4.5`10-6 +Vfm18.4`10-6 1 am=18.410"6 ac is the thermal expansion coefficient of the sintered compact named here as 15 the core am is the thermal expansion coefficient of the compact matrix and frequently of the covering shell as well.
Vfb and Vfm are the volume fraction of the W-base metal and the bronze matrix respectively.
During temperature drop from 8009C (the approximate lower solidification temperature of bronze) to 259C (the room temperature), the covering shell metal shrinks and tightly hold around the core compact, which its metal matrix and despite of its similarity to the covering shell metal, is still not yet entirely solidified, exerts compressive stress/strain on it resulting in densification and pore elimination. This process incorporates, hot pressing, sintering and infiltration, acting simultaneously and resulting in homogeneous pore free sintered composite structure.
The process of the present invention generally relates.to a process for producing a metal-matrix composite of significant L\CTE between the hard base-metal and the soft matrix, the process includes the steps of sintering, pressing and enforced infiltration of the metal-matrix composite compact wherein the process is driven by differential thermal expansion coefficients between shell and core materials.
The materials are particulate composite materials or fiber composite materials and the metal-matrix composite is composite comprising tungsten, bronze and zinc stearate binder. The composite preferably includes 50 wt% of tungsten, 49 wt% of bronze and 1 wt% of zinc stearate.
The tungsten component of the composite is ranging from 50 wt% to 90wt%. The bronze component is ranging from 10 wt% to 50 wt% wherein the zinc stearate.
binder of 1 wt% is added to the composite having pre-ally bronze component only.
The zinc stearate binder is intimately mixed with the tungsten and bronze whereas the bronze component of the composite can be pre alloyed bronze or Cu-Sn admixed bronze. The weight of the Sn element in bronze is 10 % whether it is in the pre alloyed bronze or in the Cu-Sn admixed bronze.
During pre sintering of the tungsten-bronze, the green compact is set as a core covered by bronze powder shell whereas post sintering, the tungsten-bronze composite compact becomes a concentric core in bronze solidified sphere shell.
The composite material can be a ball milled tungsten-Cu-Sn powder or as received tungsten-Cu-Sn elemental powder. The composite could be a ball milled tungsten-pre alloy bronze as well.
The material of the covering sphere shell can be as received pre-alloy bronze powder or as received Cu-Sn admix powder or as received Cu elemental powder.
The weight of the covering shell should be at least equivalent to the weight of the compact.
The densification of the tungsten-bronze compacts is conducted at a temperature ranging from 1150 C-1400 C, preferably at 1200 C under H2 or H2/N2 protective gas.
Example Tungsten-Cu-Sn composites In order to apply the "three in one densification invention" for the production of W80wt%-Cu18-Sn sintered compacts, a suitable ceramic mold with a certain cavity of required shape was fabricated.
As received tungsten powder of 12pm particle size and 99.9 purity was admixed with copper powder of <45pm particle size, 99.5 purity and tin powder of <45pm particle size and 99.8 purity. The amount of tungsten was 80wt% and the balance was Cu-SnlOwt. mix, no binder was used. The admixture was mixed manually in small glass container for 30 minutes to avoid any sort of segregation induced by the variations in particle size and density of the mixture components. Then admixture was die pressed uniaxialy under 360 MPa. The green compact disc produced was 5 gram weight of 13mm diameter and nearly 4 mm thickness and having 70% of its theoretical density..
The green compact was then placed in the ceramic mold cavity and covered all around by 5 g weight as received Cu-Sn10 wt% powder mix. The covered green compact was sintered in alumina tube furnace. The heating up rate was 8 C/min, the isothermal sintering temperature was 1150 for 3 hours and the cooling down rate was 4 C/min.
The "three in one densification invention" sintering process was conducted under H2/N2 gas of 20/80 wt ratio. Post sintering, the.mold charge was dismantled and. the solidified covering shell was machined and grinded away to extract the sintered compact. The invention yielded sintered compact of 99% theoretical density with even dispersion of the W phase in Cu-Sn matrix, homogeneous, voids and cracks free structure. The sintered compact had an average micro hardness value of 250 (Hv).
The Cu-Sn volume fraction in the sintered compact was of 36% which is very difficult to be attained by the existing conventional infiltration technology. However, by this invention, controlling the volume fraction of the soft component in the compact, which is very important factor in electronic industry applications, is not a real problem as it can be designed prior to green compact production.
The three main mechanical and physical parameters governing the "three in one densification invention" are:
= The 4CTE between the compact at the core and the covering shell.
The differential amount of the radial displacement (Ur) of the solidified compact and the surround covering shell.
= The compression stress or the radial stress (võ) induced by the differential radial displacement and becomes responsible for the compact densification.
Sintered compacts of 50-90 W wt% were produced successfully by this invention.
Sintered compacts of 80-90 W wt% showed the best results. Besides these parameters, other factors like, connectivity, contiguity and the particle size of the hard component have great effects on "the three in one densification invention"
action.
Fig. 8 (a) shows a SEM micrograph of W50wt.%-pre-alloy bronze compact of ball milled powder sintered conventionally.
Fig. 8 (b) shows a SEM micrograph of W50wt.%-pre-alloy bronze compact of ball milled powder sintered by the present invention wherein sintered density of 99%
theoretical density is achieved.
Fig. 8 (c) shows a SEM micrograph of W50wt.%-Cu45-Sn compact of two-step ball milled powder sintered conventionally.
Fig. 8 (d) shows a SEM micrograph of W50wt.%-Cu45-Sn compact of two-step ball milled powder sintered by the present invention technique wherein sintered density of 98% theoretical density is achieved.
Fig. 9 (a) shows the EDX line scan across the shell/core boarder of W50wt%-Cu45-Sn sintered compact of ball milled powder sintered by the process of the present invention.
Fig. 9 (b) shows the EDX line scan of sintered compact of similar composition of W50wt%-Cu45-Sn sintered compact of ball milled powder sintered by the present invention technique but with pre-alloy bronze matrix. The shell is of Cu element.
Fig. 10 shows the alumina ceramics mould shows the cavity in where the W-bronze green compact placed and covered all around by the Cu-Sn powder mix shell before sintering.
5 Fig. 11 shows a typical thermal and infiltration sintering cycle program of the present invention wherein the sintering, heating and cooling temperature rates can be altered according to the sintered material specifications.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention relates to a process for producing a metal-matrix composite of significant ACTE between the hard base-metal and the soft matrix. Hereinafter, this specification will describe the present invention according to the preferred embodiments of the present invention. However, it is to be understood that limiting the description to the preferred embodiments of the invention is merely to facilitate discussion of the present invention and it is envisioned that those skilled in the art may devise various modifications and equivalents without departing from the, scope of the appended claims.
The present invention is generally related to a method for producing a composite material comprising a matrix phase and a dispersed phase, in particular metal-metal, metal-ceramics/carbide or composite material, such as tungsten-bronze, tungsten-copper, AI-SiC and Al-AI203. The hard base component could be particulates, dispersoids, cermets, short or continuous fibers, monofilament or whiskers reinforcements of any material type having significantly lower CTE value than that of the matrix. The process includes hot pressing, sintering and infiltration, acting simultaneously in one stage to yield microstructure of even distribution of the dispersed phase in the metal matrix.
The "three in one densification process" relates to the sintering/infiltration of metal-metal or metal-ceramics/carbide composite material by one process comprises sintering, hot pressing and enforced infiltration acting simultaneously in one step. The objective of this invention is to produce, pore free, homogeneous sintered compact structure with minimum defects at its near theoretical density. The hard metal or ceramics reinforcements uniformly distributed in a softer metal matrix. The first stage is the preparation of the as received composite powder components, either by mixing or ball milling. Usually the composite consists of two or more components, i.e.
the hard base metal component of higher melting point like tungsten and the matrix soft component having lower melting point, like bronze or copper. The powders mixture consist of W base metal ranges between 50-90 wt percent and the balance. is pre alloyed bronze or admixture of Cu-SnlOwt%. The ball milled and the as-received admixed powders are die-pressed separately under uniaxial pressure ranges between 360-720 MPa preferably around 400 MPa to yield compact discs of 13mm diameter and around 4 mm thickness. In case of utilizing the as received hard pre-alloyed bronze powder as the compact soft component i.e.. the matrix, it is necessary to add 0.01 of zinc stearate as a binder to enhance the green compaction process, while it is not important to add any sort of binder if the compact soft component is Cu or Cu-Sn10wt% admixture. The green compact is then placed in a ceramic mold of suitable cavity, large enough to accommodate the green compact and then covered all around by Cu or bronze powder called here as the outer shell. In case of green compact being fabricated from ball milled and mechanically alloyed powders, the outer covering shell should be a single phase elemental powder; otherwise the sintered, compact suffers severe swelling induced by the divergency in diffusion pathways and powder particle size between the core and the covering shell. The composite system i.e. the green compact as a core and the covering shell is then sintered in a furnace following a pre designed sintering program comprises heating up stage at heating rate of 5-8 C/min and isothermal sintering stage at a temperature of 1150 C- 1300 C for 2-3 hours. The final stage is the cooling down stage. It is essential to pay great attention to the cooling down rate. Usually 4-8 C/min is suitable for the W composite system.
Hereinafter the detailed description of the invention will be described in accordance with the accompanying drawings which will be referred either individually or collectively, in any combination thereof, wherein:
Fig. 1 is a schematic representation of the process for producing a metal-matrix composite of significant ACTE between the hard base-metal and the soft matrix according to the preferred embodiments of the present invention. This figure.
shows that the process which is a "three in one densification process" on its ongoing action.
As the skin of the outer shell starts to solidify and as the solidification process proceeds the outer shell shrinks and compresses continuously towards the center, the compression stress builds up gradually driven by the differential thermal expansion coefficients ACTE of the shell and the compact materials at the core.
Fig. 2 shows a 3D schematic diagram of the present invention technique wherein the core is representing the W-Cu-Sn compact encircled or surrounded by Cu-Sn shell. As the shell solidifies, it shrinks and exerts compression stress on the core which enhances the core densification process.
Fig. 3 (a) shows an optical graph of W80wt.%-Cu18-Sn shell-on-core sintered compact cross section of as received elemental powder, the shell is bronze admix. The compact sintered at 1150 C for 3 hours under H2/N2 20/80 wt. ratio as protective gas utilizing the process of the present invention.
Fig. 3 (b) shows an optical graph of shell-on-core sintered compact cross section of W50wt.%-Cu45-Sn sintered compact of two-steps ball milled powder. The shell.
is copper wherein the compact is sintered at 1150 C for 3 hours under H2/N2 20/80 wt.
ratio as protective gas utilizing the process of the present invention;
Fig. 3 (c) shows an optical graph of shell-on-core sintered compact cross section of W80wt.%-Cu18-Sn sintered compact. The compact is sintered at 1150 C for 3 hours under H2/N2 20/80 wt. ratio as protective gas utilizing the process of the present invention Fig. 3 (d) shows an optical graph shell-on-core sintered compact cross section of W40wt%-pre-alloyed bronze sintered compact. The compact is sintered at 1150 C
for 3 hours under H2/N2 20/80 wt ratio protective gas utilizing the process of the present invention Fig. 4 shows the micro hardness profile across. the solidified Cu-Sn shell and the W80wt.%-Cu18-Sn sintered compact of 99% of its theoretical density.
Fig. 5 shows the SEM micrographs of W 80wt.%-Cu18-Sn sintered compacts of as received elemental powder densified by the process, in which hot pressing, sintering and infiltration process acting together. The micrographs reveal sintered compacts having 99% theoretical density. The last micrograph represents sintered compact of similar composition sintered by the conventional method of uniaxial compaction and sintering.
Fig. 6 (a) shows the optical micrographs of W80wt.%-Cu18-Sn compacts of as-received powder sintered conventionally at 1150 C for 3 hours;
Fig. 6 (b) shows the optical micrographs of W80wt.%-Cu18-Sn compacts of as-received powder sintered by the process of the present invention under similar sintering conditions as in Fig. 6 (a).
5 Fig. 6 (c) shows the optical micrographs of W90wt.%-Cu18-Sn compacts of as-received elemental powder sintered conventionally at 1150 C for 3 hours.
Fig. 6 (d) shows the optical micrographs of W90wt.%-Cu18-Sn compacts of similar composition to Fig. 6 (c) sintered by the process of the present invention under similar 10 sintering conditions as in Fig. 6 (c).
Fig. 7 shows a schematic representation of the process of the present invention at its final stage. As the sintering process elapsed and the covering shell melt cools down and gradually solidifies, it undergoes a substantial contraction driven by its high 15 thermal expansion coefficient and step by step it commences compressing and tightening firmly the core which has less thermal expansion coefficient and less contraction. This action is hot-isostatic-pressing-like action and leads to denser sintered compacts of near its theoretical density.
Fig. 8 (a) shows a SEM micrograph of W50wt.%-pre-alloy bronze compact of ball milled powder sintered conventionally.
Fig. 8 (b) shows a SEM micrograph of W50wt.%-pre-alloy bronze compact of ball milled powder sintered by the present invention wherein sintered density of 99%
theoretical density is achieved.
Fig. 8 (c) shows a SEM micrograph of W50wt.%-Cu45-Sn compact of two-step ball milled powder sintered conventionally.
Fig. 8 (d) shows a SEM micrograph of W50wt.%-Cu45-Sn compact of two-step ball milled powder sintered by the present invention technique wherein sintered density of 98% theoretical density is achieved.
Fig. 9 (a) shows the EDX line scan across the shell/core boarder of W50wt%-Cu45-Sn sintered compact of ball milled powder sintered by the process of the present invention..
Fig. 9 (b) shows the EDX line scan of sintered compact of . similar composition of W50wt%-Cu45-Sn sintered compact of ball milled powder sintered by the present invention technique but with pre-alloy bronze matrix. The shell is of Cu element.
Fig. 10 shows the alumina ceramics mould shows the cavity in where the W-bronze green compact placed and covered all around.by the Cu-Sn powder mix shell before sintering.
Fig. 11 shows a typical thermal and infiltration sintering cycle program of the present invention wherein the sintering, heating and cooling temperature rates can be altered according to the sintered material specifications.
So far, the most widely used method to attain fully dense W-bronze or W-Cu composite compacts, is to infiltrate pre sintered, porous W-base metal preforms by bronze or Cu melts. This technique proves to be costly and time consuming as it comprises many stages. In this investigation, manipulation the powder constituent physical properties of W composites has led to the implementation of exclusively novel "three in one densification invention" process includes sintering, in-situ hot isostatic pressing (HIP) and infiltration acting simultaneously at relatively low densification temperature of 1150 C under H2/N2 20/80 wt. ratio as protective gas. Pilot sintered/infiltrated compacts of = 99% theoretical density of different W (50, 80 and 90) wt.% balance is Cu-10wt.%Sn compacts of as received W, Cu and Sri metal powder precursors were produced. Other. sintered/infiltrated compact sets of W50wt.%
and W80wt.%, balance is bronze 10wt.%Sn compacts of ball milled powder mixes gave sintered density 95% of theoretical density. The compacts were subjected to density measurements, shrinkage and porosity characterization. Microstructure, hardness and densification mechanisms of the sintered/infiltrated compacts were evaluated and examined using scanning electron microscopy (SEM), energy dispersive x-ray analysis (EDX) and x-ray diffraction analysis (XRD).
During the heating up stage and the isothermal stage, sintering of the compact at the core is proceeding. The main sintering mechanisms at those two stages are,.
firstly by solid state diffusion and as the liquid phase forms particles rearrangement becomes the dominant sintering mechanism. As the temperature exceeds the shell's powder melting temperature, the powder starts to melt and wet the compact surfaces which now become a concentric core within the covering shell and forming the so called shell-core system. The melted covering shell usually assumes spherical shape under its surface tension. At this stage, the melted. shell enhances the sintering process of the core. It improves core protection from furnace environment, reduces oxidation and prevents contamination. As the heating-up stage and the isothermal stage are elapsed. The melted shell cools down and eventually starts to solidify. The solidification process proceeds gradually from the outside towards the center.
Now if the density of the solidified shell is greater than that of its liquid, the new solidified thin shell will occupies less volume than the original liquid from which it solidifies;
accordingly negative internal pressure builds up in the not-yet-solidified metal melt around the core. The magnitude of this negative internal pressure depends on the cooling rate, the solidified sphere diameter and its material physical properties (CTE of metal, metal thermal conductivity and the ratio of solid/liquid density). As far as this internal negative pressure is not counter balanced by an external force or by outer sphere surface buckling, it will experience vacuum-sintering-like effects and leads to the elimination of some voids and porosities from the core. As the solidification of the outer shell terminates, it undergoes a substantial thermal contraction due to its high CTE and starts compressing firmly and.isostaticly the compact at the core which is not solidified yet, firstly because of the heat transfer sequence and secondly because it contains tungsten particles having low heat dissipation rate and act as a thermal source. At this stage the strength modulus of the solidified covering shell is substantially higher than that of the not-yet-solidified soft component (mushy matrix) within the compact at the core. The tensile strength of bronzel0%Sn is temperature dependant. As the temperature increases from room temperature to 3009Cthe bronze metal looses around 80% of its original ultimate tensile strength.
Accordingly, the matrix component of lower strength within the core, yields under the applied external isostatic pressure and bring the W particles together and expel all voids and residual porosities out to the compact/covering shell interface leaving high dense sintered core.
The sintered compact i.e. the core remains under compressive stress even after its own matrix entirely turns to solid and its temperature reaches room temperature.
The main features of the "three in one densification invention" are.
= It is very simple and cost effective.
The weight percentages of the sintered compact components can be preliminary controlled. It is easy to increase the matrix weight percentage of the compact which is important in improving the thermal conductivity of the product.
= No need for any sort of sintering additives which can lead to non controllable shrinkage during liquid phase sintering and have negative effects on thermal conductivity of the sintered part.
= The covering shell shields the composite compact during sintering process and prevents compact oxidation and contamination.
= Post sintering/infiltration process, it is easy to salvage the outer shell machined metal for the next production batch usages.
An aspect of the present invention specifies a method for producing a composite material having matrix and dispesoid phase like W-bronze, where W is the dispesoid phase and the bronze is the matrix. The method comprises die pressing of the composite elemental powders to yield a green compact and then to place this compact.
in a ceramics mold of suitable cavity. The green compact is adjusted and placed in the cavity as a concentric core surrounded by the covering shell powder. The weight of the loose covering shell powder encircled the green compact is at least equal to its weight.
The ceramics mold and its charge are then introduced into a furnace and the green compact with the covering shell powder sinter at temperature above the shell powder melting temperature for a certain time under protective gas, hydrogen or inert gas to prevent oxidation. The compact soft component metal, called here the matrix, is usually similar to the covering shell metal unless specified otherwise. Now as the core i.e. the composite green compact gets sintered and as the temperature exceeds the 25. matrix melting temperature the liquid phase forms inside and outside the core and enhance the densification process. When the isothermal sintering stage entirely elapsed, the charge starts to cool down. The differential thermal expansion between the core material and the covering shell material leads to a different degree of contraction depending on their materials thermal expansion coefficients. At certain stage, the completely solidified shell starts contracting and exerting isostatic pressure 5 on the semi solidified core. This induced pressure and stress/strain reaches its maximum degree as the temperature drops to room temperature. The amount of the exerted stress/strain on the sintered compact at the core depends on the temperature gradient, the volume fraction of the W hard component owing .to the lower thermal expansion coefficient and the bulk volume of the core and that of the outer shell. The 10 coefficients of thermal expansion (commonly referred to as iCTE) of the W-bronze core are.
a`= VIb 4.5`10-6 +Vfm18.4`10-6 1 am=18.410"6 ac is the thermal expansion coefficient of the sintered compact named here as 15 the core am is the thermal expansion coefficient of the compact matrix and frequently of the covering shell as well.
Vfb and Vfm are the volume fraction of the W-base metal and the bronze matrix respectively.
During temperature drop from 8009C (the approximate lower solidification temperature of bronze) to 259C (the room temperature), the covering shell metal shrinks and tightly hold around the core compact, which its metal matrix and despite of its similarity to the covering shell metal, is still not yet entirely solidified, exerts compressive stress/strain on it resulting in densification and pore elimination. This process incorporates, hot pressing, sintering and infiltration, acting simultaneously and resulting in homogeneous pore free sintered composite structure.
The process of the present invention generally relates.to a process for producing a metal-matrix composite of significant L\CTE between the hard base-metal and the soft matrix, the process includes the steps of sintering, pressing and enforced infiltration of the metal-matrix composite compact wherein the process is driven by differential thermal expansion coefficients between shell and core materials.
The materials are particulate composite materials or fiber composite materials and the metal-matrix composite is composite comprising tungsten, bronze and zinc stearate binder. The composite preferably includes 50 wt% of tungsten, 49 wt% of bronze and 1 wt% of zinc stearate.
The tungsten component of the composite is ranging from 50 wt% to 90wt%. The bronze component is ranging from 10 wt% to 50 wt% wherein the zinc stearate.
binder of 1 wt% is added to the composite having pre-ally bronze component only.
The zinc stearate binder is intimately mixed with the tungsten and bronze whereas the bronze component of the composite can be pre alloyed bronze or Cu-Sn admixed bronze. The weight of the Sn element in bronze is 10 % whether it is in the pre alloyed bronze or in the Cu-Sn admixed bronze.
During pre sintering of the tungsten-bronze, the green compact is set as a core covered by bronze powder shell whereas post sintering, the tungsten-bronze composite compact becomes a concentric core in bronze solidified sphere shell.
The composite material can be a ball milled tungsten-Cu-Sn powder or as received tungsten-Cu-Sn elemental powder. The composite could be a ball milled tungsten-pre alloy bronze as well.
The material of the covering sphere shell can be as received pre-alloy bronze powder or as received Cu-Sn admix powder or as received Cu elemental powder.
The weight of the covering shell should be at least equivalent to the weight of the compact.
The densification of the tungsten-bronze compacts is conducted at a temperature ranging from 1150 C-1400 C, preferably at 1200 C under H2 or H2/N2 protective gas.
Example Tungsten-Cu-Sn composites In order to apply the "three in one densification invention" for the production of W80wt%-Cu18-Sn sintered compacts, a suitable ceramic mold with a certain cavity of required shape was fabricated.
As received tungsten powder of 12pm particle size and 99.9 purity was admixed with copper powder of <45pm particle size, 99.5 purity and tin powder of <45pm particle size and 99.8 purity. The amount of tungsten was 80wt% and the balance was Cu-SnlOwt. mix, no binder was used. The admixture was mixed manually in small glass container for 30 minutes to avoid any sort of segregation induced by the variations in particle size and density of the mixture components. Then admixture was die pressed uniaxialy under 360 MPa. The green compact disc produced was 5 gram weight of 13mm diameter and nearly 4 mm thickness and having 70% of its theoretical density..
The green compact was then placed in the ceramic mold cavity and covered all around by 5 g weight as received Cu-Sn10 wt% powder mix. The covered green compact was sintered in alumina tube furnace. The heating up rate was 8 C/min, the isothermal sintering temperature was 1150 for 3 hours and the cooling down rate was 4 C/min.
The "three in one densification invention" sintering process was conducted under H2/N2 gas of 20/80 wt ratio. Post sintering, the.mold charge was dismantled and. the solidified covering shell was machined and grinded away to extract the sintered compact. The invention yielded sintered compact of 99% theoretical density with even dispersion of the W phase in Cu-Sn matrix, homogeneous, voids and cracks free structure. The sintered compact had an average micro hardness value of 250 (Hv).
The Cu-Sn volume fraction in the sintered compact was of 36% which is very difficult to be attained by the existing conventional infiltration technology. However, by this invention, controlling the volume fraction of the soft component in the compact, which is very important factor in electronic industry applications, is not a real problem as it can be designed prior to green compact production.
The three main mechanical and physical parameters governing the "three in one densification invention" are:
= The 4CTE between the compact at the core and the covering shell.
The differential amount of the radial displacement (Ur) of the solidified compact and the surround covering shell.
= The compression stress or the radial stress (võ) induced by the differential radial displacement and becomes responsible for the compact densification.
Sintered compacts of 50-90 W wt% were produced successfully by this invention.
Sintered compacts of 80-90 W wt% showed the best results. Besides these parameters, other factors like, connectivity, contiguity and the particle size of the hard component have great effects on "the three in one densification invention"
action.
Claims (21)
1. A process for producing a metal-matrix composite made of a matrix phase and a dispersed phase materials, the process includes the steps of:
(a) preparing of composite powder components comprising the hard base-material and a soft metal matrix by mixing or ball milling;
(b) pressing the composite powder components as obtained from step (a) under a preferred pressure;
(c) sintering the composite powder components as obtained from step (b) at a preferred heating rate, temperature and time; and (d) cooling composite powder components as obtained from step (c) at a preferred cooling down rate;
wherein the process is driven by differential thermal expansion coefficients between shell and core materials.
(a) preparing of composite powder components comprising the hard base-material and a soft metal matrix by mixing or ball milling;
(b) pressing the composite powder components as obtained from step (a) under a preferred pressure;
(c) sintering the composite powder components as obtained from step (b) at a preferred heating rate, temperature and time; and (d) cooling composite powder components as obtained from step (c) at a preferred cooling down rate;
wherein the process is driven by differential thermal expansion coefficients between shell and core materials.
2. The process as claimed in claim 1, wherein the preferred pressure applied in step (b) is 360-720 MPa, preferably around 400 MPa.
3. The process as claimed in claim 1, wherein the preferred heating rate applied in step (c) is of 5-8 °C/min, temperature of 1150°C-1300°C
for a period of 2-3 hours.
for a period of 2-3 hours.
4. The process as claimed in claim 1, wherein the preferred cooling down rate is 4-8°C/min.
5. The process as claimed in claim 1, wherein the materials are particulate dispersoids, cermets, short or continuous fiber, whiskers or monofilament composite materials.
6. The process as claimed in claim 1, wherein the metal-matrix composite is composite comprising tungsten, bronze and zinc stearate binder.
7. The process as claimed in claim 6, wherein the tungsten component of the composite is ranging from 50 wt% to 90wt%.
8. The process as claimed in claim 6, wherein the bronze component is ranging from wt% to 50 wt% wherein the zinc stearate binder of 1 wt% is added to the composite having pre-ally bronze component only.
9. The process as claimed in claim 8, wherein the composite includes 50 wt% of tungsten, 49 wt% of bronze and 1 wt% of zinc stearate binder.
10. The process as claimed in claim 9, wherein densification of the tungsten-bronze compacts is conducted at a temperature ranging from 1150°C-1400°C, preferably at 1200°C under H2 or H2/N2 protective gas.
11. The process as claimed in claim 6, wherein the bronze component of the composite is pre alloyed bronze or Cu-Sn admixed bronze.
12. The process as claimed in claim 6, wherein %weight of Sn element in bronze is 10 % whether it is in pre alloyed bronze or in Cu-Sn admixed bronze.
13. The process as claimed in claim 6, wherein the composite is a ball milled tungsten-Cu-Sn powder or as received tungsten-Cu-Sn elemental powder.
14. The process as claimed in claim 6, wherein the composite could be a ball milled tungsten-pre alloy bronze.
15. The process as claimed in claim 1, wherein material of a covering sphere shell is as received pre alloy bronze powder or as received Cu-Sn admix powder or as received Cu elemental powder.
16. The process as claimed in claim 15, wherein the weight of the covering shell is at least equivalent to the weight of the compact.
17. A metal-matrix composite made of a matrix phase and a dispersed phase materials as claimed in claims 1 to 16.
18. The metal-matrix composite as claimed in claim 17, wherein the metal-matrix composite is composite comprising tungsten, bronze and zinc stearate binder.
19. The metal-matrix composite as claimed in claim 17, wherein the tungsten component of the composite is ranging from 50 wt% to 90wt%.
20. The metal-matrix composite as claimed in claim 19, wherein the bronze component is ranging from 10 wt% to 50 wt% wherein the zinc stearate binder of 1 wt% is added to the composite having pre-ally bronze component only.
21. The metal-matrix composite as claimed in claim 20, wherein, wherein the composite includes 50 wt% of tungsten, 49 wt% of bronze and 1 wt% of zinc stearate binder.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| MYPI20093421 | 2009-08-17 | ||
| MYPI20093421A MY153686A (en) | 2009-08-17 | 2009-08-17 | A process for producing a metal-matrix composite of significant ?cte between the hard base-metal and the soft matrix |
| PCT/MY2010/000115 WO2011021923A1 (en) | 2009-08-17 | 2010-07-05 | A process for producing a metal-matrix composite of significant δcte between the hard base-metal and the soft matrix |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2770464A1 true CA2770464A1 (en) | 2011-02-24 |
Family
ID=43838289
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA2770464A Abandoned CA2770464A1 (en) | 2009-08-17 | 2010-07-05 | A process for producing a metal-matrix composite of significant .delta.cte between the hard base-metal and the soft matrix |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP2467223A1 (en) |
| AU (1) | AU2010284750B9 (en) |
| CA (1) | CA2770464A1 (en) |
| MY (1) | MY153686A (en) |
| WO (1) | WO2011021923A1 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP6029222B1 (en) * | 2015-07-08 | 2016-11-24 | 有限会社 ナプラ | Metal particles, paste, molded body, and laminate |
| EP3493934A4 (en) * | 2016-08-06 | 2019-12-18 | Metallum3d Inc. | Apparatus and methods for microwave densification |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA1166043A (en) * | 1979-08-20 | 1984-04-24 | Yew-Tsung Chen | Process for producing a powder metal part |
| US5163499A (en) * | 1988-11-10 | 1992-11-17 | Lanxide Technology Company, Lp | Method of forming electronic packages |
| US5950064A (en) * | 1997-01-17 | 1999-09-07 | Olin Corporation | Lead-free shot formed by liquid phase bonding |
| CA2462977C (en) * | 2001-10-16 | 2005-08-23 | International Non-Toxic Composites Corporation | Composite material containing tungsten and bronze |
-
2009
- 2009-08-17 MY MYPI20093421A patent/MY153686A/en unknown
-
2010
- 2010-07-05 AU AU2010284750A patent/AU2010284750B9/en not_active Ceased
- 2010-07-05 EP EP10810229A patent/EP2467223A1/en not_active Withdrawn
- 2010-07-05 WO PCT/MY2010/000115 patent/WO2011021923A1/en active Application Filing
- 2010-07-05 CA CA2770464A patent/CA2770464A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| MY153686A (en) | 2015-03-13 |
| AU2010284750A1 (en) | 2012-03-15 |
| AU2010284750B2 (en) | 2014-05-08 |
| WO2011021923A1 (en) | 2011-02-24 |
| EP2467223A1 (en) | 2012-06-27 |
| AU2010284750B9 (en) | 2014-07-24 |
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