Impact behavior of Bulk Metallic Glasses
Bulk Amorphous Alloys (BAAs) are multicomponent metal alloy systems (based on Zr, Cu, Fe, Ti, Mg etc.) in a metastable, amorphous state. Compared with conventional crystalline alloys, the absence of dislocations, grain boundaries and crystalline phases in BAAs results in an extraordinary combination of properties, including: ● ultra-high-strength (twice the strength of titanium alloys); ● ultra-high-hardness (comparable to ceramics); ● elastic limits twice that of regular metals; ● excellent corrosion resistance and, in some instances, ● extremely high fracture toughness. The unique multi-dimensional property portfolio of BAAs are attracting the attention of the world’s leading space agencies (e.g. NASA & ESA) as candidate impact resistant materials for aerospace applications, however very little is known about how they respond to impact events and what are the fundamental mode/s of deformation and failure under these conditions.
To address this problem, Escobedo and Hazell have started a program to investigate the strength and fracture behaviour of BAAs under high- and hyper-velocity impact conditions. These efforts are in collaboration with researchers within The University of New South Wales (M. Ferry and K. Laws) and international institutions as Imperial College London (D. Eakins and D Chapman) and Los Alamos National Lab (EK Cerreta). Initial results on the investigation of chemical composition on the dynamic response of two BAAs with different Zr content (46 and 55%) are given in Figure 1. A standard configuration of this type of experiments is given in Fig. 1.a. The results (Fig. 1.b) show a larger drop for the Zr55 alloy (blue line), this measurement can in turn, be associated with a higher strength as compared with the Zr46 alloy. Post mortem examination of the fracture surfaces confirms the marked difference in behaviour. While the fracture surface of the Zr46 alloy is dominated by morphological features characteristic of brittle failure via shear banding (Fig. 1.c), the surface of the Zr55 exhibits a smoother profile in which a dimple structure is observed. The latter features normally associated with a plastic-like behaviour.