Preparation Of Rare Earth Modified Cobalt Coated Wc Powder And Its Spark Plasma Sintering

Cobalt was deposited on WC particle by a method similar to the one used in industrial cobalt powder production. This new method greatly simplified powder preparation in cemented carbides manufacturing. Rare earth was added in a heterogeneous basic solution by hydrazine decomposition. Compound powder produced by the new method and by mechanical milling was consolidated by SPS. The sintering temperatures were selected by results from finite element analysis of sample temperature distribution during sintering. Finally, sample mechanical properties and microstructures were examined.In compound powder preparation, two methods were investigated and one is the newly invented cobalt chemical deposition by hydrazine. Compared to commonly used chemical plating, this new method can coat WC particle with a uniform cobalt layer without too much coordinating chemicals. In powder rare earth modification, two procedures were analyzed. One was heterogeneous deposition by hydrazine decomposition, the other was of the same mechanism but by using urea instead of hydrazine. Results showed that hydrazine can prevent cobalt corrosion, so it is superior to urea.Finite element analysis results showed that sample temperature in the center is higher that the outer boundary between powder and die, and temperature differs less vertically. In addition, the highest temperature appears near the boundary between punch and powder and lies inside the punch. Overall temperature variation among different part of the sample is less than 50℃.Test results showed that chemically deposited power had a uniform microstructure and its mechanical properties were better than physically blended powders. The results also indicated that rare earth modification improved the density and mechanical properties considerably.