Mechanical properties and microstructural evolution of WC-binderless and WC-Co hard materials by the heat treatment process

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In this study, the heat treatment process was performed to improve the mechanical properties of WC-binderless and WC-Co hard materials pre-fabricated by PCAS process. The microstructural and mechanical properties were varied significantly by the heat treatment process with the treatment time. To increase the fracture toughness value, the heat-treatment process of the WC-binderless, WC-5 wt.% Co and WC-10 wt% Co hard materials were performed at (1,300, 1,150, and 950) °C under (5 and 48) h, respectively. Enhancement of fracture toughness that focused on the major reasons was estimated for four mechanisms. Firstly, the microstructure formation of a mechanism was investigated to demonstrate the grain coarsening behavior for variation of heat treatment time. Secondly, the fraction of the coherent interface at WC/Co to the existing in the specific plane orientation was investigated. In particular, the texture distribution of WC (0001)hcp plane and Co (111)fcc plane were discussed in the EBSD micrograph. Thirdly, the increase of the mean free path by the Co content was exhibited in relation to the variation of mechanical properties. Finally, the mechanism of the decarburization effect of WC, which occurs during the heat treatment process under specific condition were demonstrated in the XRD peaks and FE-SEM analysis. In this chemical reaction, the separated W phases were locally precipitated, resulting in an increase in fracture toughness.