Investigation of phase structure of cobalt and its effect in WC-Co cemented carbides before and after deep cryogenic treatment

The morphology, crystal structure and magnetic properties of cobalt in as-sintered and deep cryogenic treated WC-25 wt % Co cemented carbide was investigated with scanning electron microscopy, X-ray diffractometer (XRD) and Hc meter. The results show that there was no significant change in the morphology and crystal structure of tungsten carbide, but cobalt has undergone an obvious change in its crystal structure. As the diffraction peaks of tungsten carbide shields the peaks of cobalt, additional investigation with as-sintered and deep cryogenic treated pure-cobalt was carried out. The peak intensity of deep cryogenic treated cobalt specimens reveals the phase transformation of cobalt which shows higher ε-Co and increased coercivity. The phase change of cobalt is substantiated by the higher wear resistance exhibited by deep cryogenic treated WC-25Co cemented carbide in pin-on-disc wear testing.