Surface microstructure and mechanical property of WC-6% Co hard alloy irradiated by high current pulsed electron beam

The surface microstructure of WC-6% Co hard alloy irradiated by high current pulsed electron beam (HCPEB) at a moderate energy density of 3 J/cm2 and pulse number of 1-35 was investigated by using scanning electron microscopy, X-ray diffractometry and transmission electron microscopy. It is found that the WC particles got remelted with the increasing number of HCPEB pulses, and a flat and compact surface with micro-crack network of cell size ~several decades of μm was generated. At the same time, the rapid thermo cycles during HCPEB irradiations led to the formation of surface nano-grained microstructure on WC-6% Co hard alloy with a thickness of 0.8-1 μm. When using 20 HCPEB pulses, an optimum surface microstructure composed of a mixture of nano-grained (20-100 nm) WC1−x and Co3W9C4 phases was obtained which gave rise to a significant improvement in surface microhardness of 21.8 GPa and wear resistance by 4 times. The performance of irradiated surface would be deteriorated by overused HCPEB irradiations due to the excessive dissolution of WC hard particles and the large amplitude of residual tensile stress accompanied by severe surface cracking and local cavity defects.