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.