Ultra-high cycle fatigue properties in Zr₅₅Al ₁₀Ni₅Cu₃₀ metallic glassy alloy using ultrasonic fatigue testing machine

In this work, the ultra-high cycle fatigue behavior of Zr ₅₅Al₁₀Ni₅Cu₃₀ metallic glass was investigated by using an ultrasonic fatigue testing method. Test alloy rods with a diameter of 8mm were prepared by tilt-casting with a copper mold. Test specimens were machined to hourglass shape (the minimum diameter ; 2.0mm), and then manually polished with polishing paste. They were tested at a frequency of 20kHz under a stress ratio of-1. The fatigue limit (σw) (half a total stress amplitude) and fatigue ratio (σw/σB) of the alloy were 893MPa and 0.53, respectively. Furthermore, no fish-eye like crack-growth morphology was seen on the fracture surfaces. The initiation region of fatigue cracking was always observed on the side surface of the specimens. A viscous-flow fracture region with large dimples between the fatigue crack-growth region and the final unstable fracture region was observed. This peculiar fracture morphology may be due to adiabatic heating of the metallic glass specimens during the fracturing, resulting in transition to supercooled liquid, under extremely high frequency of fatigue stress using ultrasonic loading.