Powder metallurgy processes – Powder metallurgy processes with heating or sintering – Powder pretreatment
Reexamination Certificate
2001-08-20
2003-05-13
Mai, Ngoclan (Department: 1742)
Powder metallurgy processes
Powder metallurgy processes with heating or sintering
Powder pretreatment
C419S019000, C419S036000, C419S048000
Reexamination Certificate
active
06562290
ABSTRACT:
BACKGROUND
The present invention relates to a process for the production of metallic and metal-ceramic composite components from composite powders, in particular based on molybdenum/copper and tungsten/copper, by powder injection molding (PIM). The invention furthermore relates to molybdenum/copper and tungsten/copper composite powders having a low primary metal particle size and optionally containing ceramic additives, to their preparation, and to their use for the production of composite components.
Metallic and metal-ceramic composite materials are widely used as special materials, for example in plant, apparatus and equipment construction. Tungsten/copper and molybdenum/copper composite materials are employed in various electrical and electronic applications owing to their comparatively high thermal conductivity. For example, these materials are increasingly being used for various applications in information, communications and transport technology as so-called “heat sinks”, “heat spreaders” and “packagings”. In addition, components made from composite materials based on tungsten/copper or molybdenum/copper are employed as electrical contacts, spot-welding electrodes, for electro-discharge machining, for power switches and for commutator materials owing to their good conductivity and high wear resistance.
For the production of composite components, various processes are known, particular importance being ascribed to powder injection molding (PIM). In this process, a suitable powder mixture comprising the desired metals and optionally further additives is mixed with a so-called binder. This mixture is homogenized, compressed, debindered and sintered.
The quality of the resultant composite components is crucially affected by the quality and composition of the composite powder employed or of the composite powder/binder mixture. Composite powder/binder mixture is also referred to as the feedstock. In particular in the case of processing of composite powders based on tungsten/copper and molybdenum/copper, it is difficult to obtain composite components with densities which are close to the theoretically possible density. It is likewise problematic to maintain tolerance values of ±0.1% for the component dimensions.
U.S. Pat. No. 5,993,731 and U.S. Pat. No. 5,686,676 propose producing metal composite components, in particular tungsten/copper and molybdenum/copper composite components, by metal powder injection molding, where, besides metal, the component subjected to the sintering process also contains chemically bound oxygen, for example in the form of metal oxides. Oxygen must be present in sufficient amount in the mixture in order to improve the sintering properties of the mixture. The sintering is carried out in a reducing atmosphere, with the oxygen present being removed little by little as far as a technically possible minimum value. According to the examples, tungsten/copper and molybdenum/copper composite components having a density which corresponds to about 98% of the theoretical density can be obtained in this way. However, it is problematic here that the composite components still contain relatively large amounts of oxygen in the form of metal oxides before the sintering. Oxygen remaining in the component is dissolved in the copper lattice during conventional liquid-phase sintering and can thus have an adverse effect on the component properties. It is not ensured that the oxygen present in the starting mixture is virtually completely degraded in this process and does not diffuse into the copper structure.
U.S. Pat. No. 5,905,938 describes a process for the production of tungsten/copper and molybdenum/copper composite components starting from tungsten and/or molybdenum powder having a particle size of up to 1 &mgr;m and copper powder having a particle size of up to 7 &mgr;m. The copper powder can also be replaced by copper oxide powder, where the copper oxide must be reduced during the sintering. In order to improve the sintering behaviour, metals from the iron group (Fe, Co and Ni) and phosphorus must be added. This pressure has the disadvantage that it is again not ensured that the composite component is substantially oxygen free. In addition, the cell conductivity of the copper matrix is significantly reduced even by small proportions of iron, cobalt or nickel.
U.S. Pat. No. 5,950,063 and U.S. Pat. No. 5,641,920 disclose various ways of preparing starting mixtures which are particularly suitable for further processing by powder injection molding. Thus, it is proposed to mix the individual components of the binder in an inert atmosphere. The mixing of binder and powder system should also be carried out in an inert atmosphere. This prevents components of the binder of low molecular weight being oxidatively decomposed. However, it is not pointed out that it could be advantageous to protect the powder system against contact with oxygen, in particular through the addition of a protecting liquid, even before the mixing with the binder.
In the processes described for the production of metal composite components by metal powder injection molding, metal powder/binder mixtures which, besides the metals, also contain oxygen are processed. The presence of oxygen is problematic, since it can dissolve in the metal lattice during sintering. In the case of molybdenum/copper and tungsten/copper composite components, the oxygen dissolved in the copper lattice results in an undesired decrease in the thermal conductivity.
The object of the present invention was to provide a process for the production of metallic and metal-ceramic composite components, in particular based on molybdenum/copper and tungsten/copper, by powder injection molding with which composite powders can be converted in a simple manner into high-quality products. A further object was to provide composite powders based on molybdenum/copper and tungsten/copper which are particularly suitable for processing by powder injection molding.
SUMMARY
The invention relates to a process for producing a composite component comprising: (a) mixing a metal composite powder with a protecting liquid in an inert atmosphere, (b) mixing the metal composite powder formed in step (a) with a binder and forming a system comprising the metal composite powder and the binder, and (c) subjecting the system to powder injection molding and forming the composite component.
The invention also relates to a process for producing a composite component comprising: (a) producing a metal composite powder by reduction of oxides of at least two different metals with hydrogen, (b) mixing the metal composite powder with a protecting liquid in an inert atmosphere and forming a metal composite powder product, (c) mixing the metal composite powder product of step b) with a binder and forming a composite powder/binder mixture, and (d) subjecting the composite powder/binder mixture to injection-molding and forming the composite component.
The invention also relates to a molybdenum/copper composite powder comprising a primary metal particle size of predominantly less than about 2 &mgr;m and an oxygen content of less than about 0.8% by weight.
The invention also relates to a tungsten/copper composite powder comprising a primary metal particle size of predominantly less than about 2 &mgr;m and an oxygen content of less than about 0.8% by weight.
In one embodiment, the invention relates to a process for forming a molybdenum/copper composite powder comprising a primary metal particle size of predominantly less than about 2 &mgr;m and an oxygen content of less than about 0.8% by weight, the process comprising: (a) mixing oxides of molybdenum and of copper and forming a mixture, and (b) dry-grounding and reducing the mixture with dry hydrogen at a temperature ranging from about 800 to about 1050° C. and forming the composite powder.
In another embodiment, the invention relates to a process for forming a tungsten/copper composite powder, wherein it has a primary metal particle size of predominantly less than about 2 &mgr;m and an oxygen content of less than about 0.
Fister Dietmar
Knüwer Matthias
Meinhardt Helmut
Meyer Bernd
Wiezoreck Wolfgang
Akorli Godfried R.
Eyl Diderico van
H.C. Starck Inc.
Mai Ngoclan
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