Abstract
Bending and compressive fatigue characteristics of WC-Co alloys were mainly investigated and discussed relating to structural defects, surface residual stress or coercive force in the alloy. The bending fatigue was influenced by the structural defects such as pore, WC and Co pool acting as a fatigue fracture origin. Especially, the fracture origin of Co pool with a step shaped form peculiar to the bending fatigue was often observed in HIP-treated alloys. Therefore, the fatigue life in micro-grain alloy was improved with the decrease of Co pool size. As to the effect of surface condition, the fatigue life was remarkably influenced by compressive residual stress of the ground surface rather than surface roughness, while the decrease of the fatigue life by coating treatment could be explained by residual stress of the coated layer and base alloy or adhesion between them. On the other hand, the compressive fatigue was not influenced by the structural defects, but it showed a positive correlation with the variation of the coercive force influenced by fatigue hardening in Co phase. Namely, the coercive force of the medium-grain alloy increased with increasing applied stress and repeated cycle, and it became much larger in the repeated compressive fatigue test than static compressive test.
