Fabrication and micro-structure of a multilayer functionally graded (WC–Co)–Ni composite

•A multilayer functionally graded (WC–Co)–Ni composite (MFGWC) was successfully fabricated.•The transitional zones formed between two layers are the crucial part of MFGWC.•Liquid phase sintering greatly influences the forming process of MFGWC.•The micro-hardness of MFGWC gradually decreases along the gradient direction.

In order to improve the welding performance of WC–Co to steel, a multilayer functionally graded (WC–Co)–Ni composite (MFGWC) was successfully fabricated by sintering the multilayer green compact, and a Ni-rich layer was covered on the compact surface. The microstructure, composition and micro-hardness of the MFGWC were investigated in this paper, results showed that the MFGWC was composed of WC–Co substrate, multi-transitional layers and pure Ni layer. The key part, multi-transitional layers formed between Ni layer and WC–Co substrate, was obtained successfully. The micro-hardness of the composite gradually decreased from 1300 HV to 66 HV along the direction of WC–Co substrate to pure Ni layer, this was due to a decrease in the amount of WC particles and the corresponding increase of Ni phases. The multi-transitional layer played a role in reducing the residual stresses that were induced by the difference of thermal expansion between WC–Co substrate and steel.