Understanding how to predict the fatigue lifetimes of bulk-metallic glass (BMG) materials is crucially important for their selection as structural alloys. In our paper, the nature of likely fatigue mechanisms for BMGs is revealed. Fatigue cracks, arising from machining/polishing damage, were experimentally observed to initiate from shear bands near defects. At the crack tip, a plastic-zone creation is observed through the formation of many shear bands, and the fatigue crack is found to propagate along these shear bands. The size of the plastic zone can be characterized by fracture-mechanics quantities, and each fatigue cycle is seen to produce a fine striation instead of a single coarse one. We propose a shear-band mechanism to explain the characteristics of the observed fatigue cracking. Numerical computations, based on linear-elastic- fracture mechanics, yield reasonably good agreement with experiments. Our findings are significant to predict the fatigue lifetimes of these materials.
ASJC Scopus subject areas
- Physics and Astronomy(all)