Fatigue crack initiation and small-crack propagation in Zr-based bulk metallic glass

Fatigue tests on Zr-based bulk metallic glass were conducted under fully reversed cyclic bending (R = - 1), and the surfaces of the fatigued specimen were observed to elucidate the fatigue crack initiation mechanisms. The fracture surface was also observed to examine the crack propagation mechanism. In contrast to most brittle materials, the metallic glass showed fatigue behavior. Its fatigue Strength was much lower than its tensile strength, and it had a fatigue limit. In the S-N curve, the number of cycles at the knee point was much lower than that for crystalline metals. The fatigue crack initiation process observed by atomic force microscopy (AFM) showed that cracks were initiated at the bottom of shear steps just after their formation.