Effect of strain rate on the size of dimple and periodic nano-corrugation patterns on the fracture surfaces of a Zr-based bulk metallic glass tested at cryogenic temperatures
Paper ID : 1049-ICNS (R1)
Authors:
Mohammad Taghi Asadi Khanouki *
Department of Materials Engineering and Metallurgy, Shahid Bahonar University of Kerman, Kerman, Iran
Abstract:
In this research, after three-point bending tests of a Zr-based bulk metallic glass at 77 K and different strain rates ranging from 1.6 × 10-4 to 1.6 × 10-2 s-1, the fracture surfaces were analysed by SEM. Results indicate that the fracture at 77 K occurs in a brittle manner. However, the appearance of dimple structure on the fracture surface indicating a type of ductile fracture mechanism in this alloy. The observation of nanoscale periodic corrugation confirms that the fracture still proceeds through the local softening mechanism but at different length scales. At 77 K, the activation of diffusion mediated phenomena is negligible and plastic deformation in BMG occurs via the operation of shear transformation zones at a characteristic time scale. Therefore, with increasing strain rate, the STZ operation occurs more instantaneously with a time scale equivalent to the inverse of strain rate, and very few or only one shear band can be activated. According to findings, the dimple and nano-corrugation size decreases with the increasing strain rate. This means that the increase of strain rate causes deteriorating ductility in microscale, and is accompanied by a lower activation of STZs, i.e. severe shear localization, which decreases the plastic zone size.
Keywords:
Bulk metallic glass; Strain rate; Shear transformation zone; Dimple; Nano-corrugations;
Status : Abstract Accepted (Poster Presentation)