Comparison of the microstructure and mechanical properties of WC-Ti(C, N)-Ni gradient cemented carbides prepared by SPS pre-sintering and vacuum pre-sintering

Abstract

Two-step sintering to prepare gradient cemented carbides tends to the grain growth of hard phases, which adversely affects the mechanical properties. Spark plasma sintering is a promising pre-sintering process to mitigate grain growth by rapid prototyping and densification. In the present work, gradient cemented carbides with Ni binder instead of traditional Co binder were fabricated by both SPS pre-sintering and vacuum pre-sintering, followed by gradient sintering. The microstructure and elemental distributions of the prepared gradient cemented carbides were thoroughly investigated by XRD, SEM, EDS, EPMA and EBSD, focusing on the gradient layer formation and WC grain growth. The influence of WC grain size on the gradient layer formation was discussed with the aid of the DICTRA simulation. Finer WC grains in the SPS pre-sintered alloy show a smaller tortuosity factor, resulting in a thicker thickness of the gradient surface layer. The variations of hardness from the surface to the interior and the fracture toughness of the bulk for the gradient cemented carbides with different pre-sintering methods were measured through the micro-indentation method. Higher hardness and fracture toughness were obtained by SPS pre-sintered gradient cemented carbide.