Processing issues for cryomilled WC-Co nanopowders : Nano-Hetero Structures in Advanced Metallic Materials

Processing issues of cryomilled WC-VC-Co nanopowders were investigated. A powder mixture of WC-9.8Co-0.8VC-xC was milled at -50°C in liquid nitrogen, using WC-Co balls. The particle sizes of the powders, in the form of agglomerates, were reduced to 18 nm and 13 nm for WC and Co, respectively by this process. The roles of some of the processing parameters such as compacting pressure, reduction of powders, and temperatures for the heating schedule were evaluated at a sintering temperature of 1450°C. The use of CIP resulted in a more uniform microstructure and enhanced mechanical properties: hardness (13-14 GPa) and K IC (12-15 MPam 1/2 ). The findings herein suggest that carbon control and the use of a proper compaction technique were key factors in the successful production of nano-sized WC-Co alloys with no detectable η phase.