Very High Cycle Fatigue Characteristics of Zr-Base Bulk Amorphous Alloy in Rotating Bending

概要

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In order to investigate very high cycle fatigue characteristics of the Zr55Al10Ni5Cu30 (in at.%) bulk amorphous alloy, fatigue tests were performed in rotating bending at a frequency of 52.5 Hz with a stress ratio of R=-1. The test environment was in room atmosphere without any control of temperature nor humidity. The fatigue endurance limit σw of the bulk amorphous alloy was about 700 MPa and the fatigue strength ratio σw/σB (fatigue endurance limit divided by the ultimate tensile strength) was found to be 0.38. Fracture surfaces of failed specimens were observed by scanning electron microscope (SEM). The fracture surface was separated into three typical regions; (1) multi-facet region, (2) stable crack propagation region and (3) instantaneous fracture region. The cracks took place on the specimen surface and fatigue striations were clearly formed in the stable crack propagation region on the fracture surface. A distinct boundary was observed between the stable crack propagation region and instantaneous fracture region. The instantaneous fracture region was covered by the dimple-type morphology. Vein-like patterns peculiar to the static fracture surface of amorphous alloys were also found in the edge region of the fracture surface. The fatigue fracture toughness of this bulk amorphous alloy was in the range of 20-29 MPa·m1/2.