Microstructure and mechanical properties of ultra-fine WC-10Co hardmetals

The mechanical properties of ultra-fine WC-10 wt.%Co-X hardmetals were investigated. Ultra-fine precursor powders were prepared by spray drying of solution containing AMT and cobalt nitrate. The precursor powders were reduced and carbonized into WC/Co powders by mechano-chemical process. The WC powders were about 100 nm in diameter and were mixed homogeneously with Co binder. The powders were wet ball-milled in n-Hexane with ball-to-powder ratio of 5:1 for 24 hrs and dried for 24 hrs. The milled powders were sintered at 1375 oC under a pressure of 1 mtorr. In order to compare the microstructures and mechanical properties with ultra-fine hardmetals, the commercial WC powders with 0.57-4 μm in diameter were mixed with Co powders, and were followed by sintering at 1375 oC under a pressure of 1 mtorr. Varying amount of TaC, Cr3C2 and VC were added into ultra-fine WC-10 wt.%Co hardmetals as grain growth inhibitors. It was observed that Co phase was precipitated within faceted WC grains in sintered ultra-fine hardmetals. The hardness of WC-10 wt.%Co hardmetals increased with decreasing WC grain size following the Hall-Petch type relationship. The transverse rupture strengths of WC-10 wt.%Co hardmetals were dependent on the solute contents within the Co binder phase. (author)