Effects of addition of ultrafine WC and fine WC/Co on microstructure and mechanical properties of WC-10Co cemented carbides

Abstract

The ultrafine WC powders with particle size of 0.5 μm were coated by nano Co particles for preparation of the fine WC/Co powder. Then it was mixed with the coarse WC and Co powders, following compacted and sintered in vacuum at 1420 ℃ for 1 h for obtaining the WC-10Co cemented carbides. The morphology, the grain structure, hardness, bending strength and fracture toughness of WC-10Co cemented carbides with the fine WC/Co and ultrafine WC for comparison were investigated by scanning electron microscopy, transmission electron microscope, universal testing machine, etc. The results reveal that the addition of the fine WC/Co has greater influence on the densification of WC-10Co cemented carbides than the ultrafine WC, and can form the dual-grained structure with a mean WC grain size of 2.18 μm, and the WC-10Co with ultrafine WC has a mean WC grain size of 3.57 μm. The WC-10Co with fine WC/Co can reduce grain growth rate and hinder dissolution of the fine grains, resulting in generation of coarse grains with truncated triangular prism and stepped surface by defect-assisted and dissolution-precipitation mechanism. The WC-10Co with fine WC/Co can improve both hardness and fracture toughness, 1131HV30 and 22.1 MPa·m1/2, respectively. Furthermore, with the same hardness of 1131HV30, its fracture toughness is 27.7% higher than linear fitted fracture. The mechanism analysis shows that the addition of ultrafine WC will lead to the formation of abnormal grains, which is not conductive to the performance; while the addition of fine WC/Co simultaneously forms the dual-grained structure and uniform Co distribution structure and reduces the defects in the grains, improves the comprehensive properties.

Keywords

• wc-10co cemented carbide
• fine wc/co additive
• ultrafine wc additive
• microstructure
• mechanical property