Effect of deep cryogenic treatment on the fracture toughness and wear resistance of WC-Co cemented carbides

The main failure causes of cemented carbide tools are fracture and wear. However, for the most of cemented carbide materials, fracture toughness can usually be increased at the expense of wear resistance by traditional modification technologies. In the present investigation, a novel method, deep cryogenic treatment, is conducted to optimize the properties of WC-20Co cemented carbides. The methods of optical microscopy (OM) and scanning electron microscopy (SEM) are used to detect and analyze the fracture paths, fractographic features and worn surfaces of cemented carbides before and after deep cryogenic treatment. The changes of microstructure are examined by SEM and X-ray diffractometer (XRD). The results show that deep cryogenic treatment can improve both fracture toughness and wear resistance of WC-20Co cemented carbides successfully. Compared to the as-sintered specimens, there exist more trans-crystalline fracture, micro-cracks and torn metallic zones in the fracture morphology, and less wear and spelling on the worn surfaces in cryogenically treated specimens. The enhancement of fracture toughness can be attributed to densification and homogenization caused by deep cryogenic treatment. The main reason for the improved wear resistance is that deep cryogenic treatment has promoted the martensitic transformation of fcc alpha-Co into hcp epsilon-Co.