Evolution of shear bands and fatigue striations in a bulk metallic glass during fatigue

Four-point-bend fatigue experiments are conducted on rectangular beam samples of a Zr50Cu37Al10Pd3 (in atomic percent) bulk metallic glass (BMG). In general, a fatigue crack initiates from the corner of the beam sample at the tensile stress surface and subsequently grows inside during cyclic loading. As a result, many shear bands form around the crack growth path due to the plastic deformation at the crack tip. Moreover, the size of the shear-band zone shows a good relationship with the stress intensity factor range, which is similar to the plastic zone in the crystalline alloys. Moreover, the shear-band spacing is consistent with the coarse fatigue striation spacing, which implies that the fatigue-crack growth in BMGs is related to the formation of shear bands. A reasonable mechanism is proposed to understand the fatigue-crack-growth behavior in BMGs.