Tungsten Powder and W-Cu Composite Powder II

It is an object of the invention to obviate the disadvantages of the prior art.

It is another object of the invention to produce a W-Cu composite powder which can be used to make W-Cu pseudoalloys having high electrical and thermal conductivities.

It is a further object of the invention to produce a W-Cu composite powder which may be pressed and sintered to near theoretical density without copper bleedout.

It is still a further object of the invention to produce a W-Cu composite powder which may be used to make sintered articles having a high degree of dimensional control.

In accordance with one object the of invention, there is provided a tungsten-copper composite powder comprising individual particles having a tungsten phase and a copper phase wherein the tungsten phase substantially encapsulates the copper phase.

In accordance with another object of the invention, there is provided a W-Cu composite oxide powder comprising individual particles having a copper tungstate phase and tungsten trioxide phase wherein the tungsten trioxide phase exists primarily at the surface of the individual particles.

In accordance with a further object of the invention, there is provided a method for forming a homogeneous W-Cu pseudoalloy comprising pressing a tungsten-coated copper composite powder to form a compact and sintering the compact.

In accordance with a still further object of the invention, there is provided a W-Cu pseudoalloy having a microstructural cross-section having tungsten areas and copper areas, the tungsten areas being less than about 5 µm in size and the copper areas being less than about 10 µm in size.

Several factors influence the solid-state (below 1083°C - the melting point of copper) and liquid-phase (above the melting point of copper) sintering behavior of submicron W-Cu powder systems. Compacted refractory metal powders undergo considerable microstructural changes and shrinkage during solid-state sintering (in the absence of liquid phase). Submicron particle size powders effectively recrystallize and sinter at temperatures (T) which are much lower than the melting temperatures (Tm) of refractory metals (T ≅ 0.3 Tm). The initial sintering temperature for submicron (0.09-0.16 µm) tungsten powder is in the range of 900-1000°C. The spreading of copper and the formation of a monolayer copper coating on tungsten particles occurs in the temperature range of 1000-1083°C. By lowering the activation energy for tungsten diffusion, monolayer copper coatings activate the solid-state sintering of tungsten. Therefore, a number of complementary conditions are met for bonding submicron tungsten particles into a rigid tungsten framework within the composite powder compact during solid-state sintering (950-1080°C). High fineness and homogeneity of the starting composite powders are expected to enhance the sintering of a structurally homogeneous tungsten framework. Such framework should, in turn, aid in making a homogeneous pseudoalloy.

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