Production And Sintering Property Of Ultra-fine W-Cu And Mo-Cu Powders

W-Cu and Mo-Cu materials have been of great interest in many high and new technology applications. They have been used as heavy-duty electronic contacts, heavy- duty circuit breakers and thermal management devices, and so on, because of their unique properties of superior thermal and electronic managements and high microwave absorption capacity etc. The properties of W(Mo)-Cu alloys depend on their densification. Due to the mutual insolubility between W(Mo) and Cu and the high contact angle of liquid copper on tungsten and molybdenum, W(Mo)-Cu alloy compacts can hardly reach a high densification by the conventional methods such as infiltration or liquid phase sintering (LPS), especially with high W(Mo) contents.The ultra-fine particle size and homogeneous distribution of ingredients in the starting powders could highly improve the sinterability of the powders. This is more important for W(Mo)-Cu systems, in which the main densification mechanism is the rearrangement of W(Mo) particles in Cu liquid during liquid phase sintering. In this dissertation, two novel methods namely airflow-crushing and coreduction and gelation-coreduction were designed to produce ultra-fine W(Mo)-Cu composite powder.W-Cu nanopowders were successfully prepared by an airflow-crushing and coreduction method, in which WO₃ and CuO powders were first crushed in a high pressure airflow, then co-reduced in H₂ to convert into W-Cu composite powders. The WO₃ and CuO powders, as well as the resulting W-Cu powders were characterized by X-ray diffraction analysis (XRD), Transmission electron microscope (TEM). Subsequently W-Cu sintered parts were prepared by compacting the W-Cu powders in a rigid die and sintering the compacts in H₂. The micro structure and properties of the sintered W-Cu parts were characterized by scanning electron microscope (SEM), universal material test machine etc. It was shown that airflow crushing effectively reduces the particle size of the starting WO₃ and CuO powders. W-Cu powders with nanosize of 50 to 100nm were obtained by coreduction the airflow crushed WO₃-CuO powder mixes in H₂. The W-Cu powder exhibits high sinterability. Density of more than 98% of the theoretical was obtained for W-Cu compacts sintered at 1200℃for 2h. Furthermore, the sintered W-Cu parts showed good physical and mechanical properties. The bending strength and Vickers hardness are more than 1000 MPa and 300 MPa, respectively, and the electrical conductivity is 35.76% IACS.Mo-Cu composite powders were prepared by a gelation-coreduction method, in which gelcasts were first obtained from precursors of (NH₄)₆Mo₇O₂₄·4H₂O and CuO powders by the crosslinking agents of acrylamide and methylene-dimalonic acrylamide. The gelcasts were then calcined at 600℃and coreduced at 700℃in H₂ to convert into Mo-Cu powders. Phase constitute and morphology of the caicined gelcasts, as well as the Mo-Cu composite powders were characheterized by X-ray diffraction analysis and transmission electron microscope. The Mo-Cu powders were die-pressed and sintered in H₂ atmosphere at temperature ranging 1050-1150℃. Physical and mechanical properties of the sintered Mo-Cu materials were tested, and microstructure observed by scanning electron microscope. It was shown that Mo-Cu composite powders with a mean particle size of about 200nm were obtained by the gel-reduction method. The powders exhibit a good dispersion of Mo and Cu ingredients and high sinterability. A relative density of 99.65% of the theoretical was achieved for Mo-Cu composites sintered at 1150℃for 90min in H₂. Furthermore, the prepared Mo-Cu materials showed good physical and mechanical properties. The bending strength and Vickers hardness are 841.54MPa and 201.60 MPa, respectively, and the electrical conductivity is 41.67% IACS.