Amorphous structure of binary Ca61Al39 metallic glass close to transition temperature

Ca-based bulk metallic glasses (BMG) with their unique properties being very low density, good compressive strength and shear modulus comparable to modulus of human bones have found utility in biomedical field. Their poor oxidation and corrosion resistance can be improved substantially when they are synthesized in a glassy state. Although, according to the confusion principle, the bulk form of binary metallic system is seldom possible; recent experimental studies have aimed to achieve these goals and succeeded in preparing CaxAly binary BMG with (x, y) pair as (8, 3), (13,14) and (61, 39). We examine and verify the amorphous structure and glass forming temperature of binary Ca61Al39(at.%) metallic glass using molecular dynamics simulations combined with an evanescent form for interaction potential at the experimental density. Good agreement is observed with recent in-situ high energy X-ray experimental findings for pair-correlation function g(r) and static structure factor S(q). Evidenced from the structural analysis, the estimated liquid to glass transition temperature (Tg) is found between 520 to 555 K. Large principal peak heights in g(r) and S(q) is attributed to the strongness of the potential, whereas the large-r Friedel oscillations results in to the oscillatory behavior of g(r). Nevertheless, present result for co-ordination number (NC) 12.44 to 12.79 is in excellent agreement with the experimental value 11.9 ± 0.3 at Tg, and changes by about 7.6% when temperature is varied from 300 to 1200 K while keeping the density constant. Unlike the other composition pair (x, y) for Ca-based BMG, a large co-ordination number is suggestive, and proposes a closed packed structure in its probable solid phase. Since the closed packed structures are commonly observed with metallic materials, this proposition is partly supported by a successful application of the evanescent form for bare-ion local pseudopotential to analyze the structural aspect of binary Ca61Al39 metallic glass.