WC-12% Co超硬合金の引張・圧縮疲労破面

抄録

A fractographic study on fatigue of WC-12% Co hardmetal under tension-compression loading was made by using SEM and EDX at various stress ratios, namely, R=0, -1, -4, -9 and -∞ (compression fatigue), where R is the stress ratio σ_min/σ_max. Under R=0 and -1, fatigue cracks were initiated from the inside of the specimen, where cleavage fracture and high concentration of Co were always found. These results seem to suggest that the fatigue cracks in these cases were initiated from the cleavage of hcp Co transformed from fcc Co existing in the as-sintered state, due to cyclic straining. On the other hand, in compression fatigue (R=-∞) and tension-compression fatigue (R=-4, -9), in which σ_max is lower than the fatigue limit in tensile fatigue (R=0 and -1), fracture was initiated from the surface of the specimen. The fracture origins in these cases were grooves formed by the dropping of the surface layer of the specimens. In these cases (R=-4, -9 and -∞) no concentration of Co was found by EDX in the area of fracture initiation.