Effects of residual thermal stress on mechanical behavior of cermets with different grain sizes

The distribution of the residual thermal stress (RTS) in the as-sintered cermets and its interactions with the applied stress were studied by simulations and experiments, using the WC-Co cemented carbides as examples. The influences of grain size, grain morphology and phase configuration on the stress state and mechanical behavior were quantified in the model, which was constructed from real multi-phased microstructures. The results indicate that the volume-averaged RTS is a power function of the mean WC grain size. There is a high level of compressive stress in the WC regions near the triple junctions of adjacent WC grains and Co binder, and a high level of tensile stress inside the Co phase in the vicinity of WC/Co phase boundaries. In the cermets with RTS, the metallic binder exhibits a gradually increasing strain response rate under the external loading. It is found that a smaller WC grain size, a lower proportion of Co thin-layers, and a higher fraction of triple junctions of adjacent WC grains and Co phase, are beneficial to have less stress concentration and simultaneously high strength and fracture toughness of the cermets. This study provides a new approach to characterize stresses in the multi-phased materials and a strategy to adjust stress distribution by tailoring the microstructure for excellent comprehensive mechanical properties.