Original Paper(Vol.62 No.3 pp.191-196)

Ultra-High Cycle Fatigue Properties in Zr55Al10Ni5Cu30 Metallic Glassy Alloy Using Ultrasonic Fatigue Testing Machine

Shin-ichi YAMAURA and Kazutaka FUJITA

Abstract:In this work, the ultra-high fatigue fracture behavior of the Zr55Al10Ni5Cu30 metallic glass was investigated by using ultrasonic fatigue testing method. The test alloy rods with a diameter of 8 mm were prepared by tilt-casting with copper mold. The test specimens were machined to hourglass shape type (the minimum diameter; 2.0 mm), and after machining the surface of the specimens was manually polished with polishing paste. The specimens were tested at a frequency of 20 kHz under a stress ratio of -1. The fatigue limit (ƒÐw) (half a total stress amplitude) and fatigue ratio (ƒÐw/ƒÐB) of the alloy show 893 MPa and 0.53, respectively. Furthermore, we did not see any fish-eye like crack-growth morphology on fracture surfaces. The initiation region of fatigue crack was always observed at the surface of the specimens. A viscous-flow fracture region with large dimples between the fatigue crack-growth region and the final unstable fracture region were observed. This peculiar fracture morphology may be due to adiabatic heating of the metallic glass during the fracture, resulting in transition to supercooled liquid, under extremely high frequency of fatigue stress using ultrasonic loading.

Key Words:Amorphous, Giga cycle fatigue, Fractography, Ultrasonic fatigue, Metallic glass, Supercooled liquid