Two-material powder injection molding of functionally graded WC–Co components

Functionally graded cemented tungsten carbide (WC–Co) components with graded cobalt concentrations have been developed to offer solutions to the tradeoff between wear resistance and fracture toughness. However, the problem of cobalt homogenization during liquid phase sintering is currently still a challenge. This paper presents the two-material powder injection molding (PIM) of functionally graded WC–Co components without cobalt concentration gradients. The powder compositions of the outer layer and core layer of the molded ring are WC–0.5 wt%Co–0.5 wt%VC–4.5 wt%W and WC–0.6 wt%Co respectively. The PIM process facilitates abnormal grain growth as a result of the loose powder structure that is present after debinding. The loose powder compact facilitates rearrangement and grain boundary formation and consequently facilitates abnormal grain growth during sintering process. The abnormal grains serve to toughen the core layer of the component. VC diffusion generates a graded microstructure in terms of the density of abnormal grains varying radially from the initial boundary to the core layer. The graded microstructure results in a gradual decrease in hardness from the outer layer to the core layer.