Thermophysical properties and solidification behavior of liquid Vit106a in microgravity

Kurzfassung

In this study, we investigate the effects of thermal history, gravitational environment, and processing conditions on the vitrification and crystallization behavior of Vit106a bulk metallic glass (BMG) alloys. Samples were processed either on ground using arc melting, or in short-term and long-term microgravity conditions in parabolic flight and aboard the International Space Station (ISS) using electromagnetic levitation (EML). Despite employing a two-step synthesis approach with a Nb–Ni pre-alloy, large Nb-rich regions were observed in the lower sections of Earth and parabolic flight samples, indicating gravitational segregation of Nb due to its high density and limited reactivity. In contrast, no such segregation was observed in the ISS-processed sample, suggesting that microgravity, possibly suppressed density-driven separation. The critical cooling rate for achieving vitrification in a 6.5 mm diameter Vit106a sphere exceeds 30 K s−1, much higher than previously reported for smaller samples of 2 mm diameter, highlighting the scale sensitivity of vitrification probably due to strong sensitivity to heterogenous nucleation. However, glass-forming ability cannot be described only by cooling rate. Our results demonstrate that liquid-state processing conditions play a decisive role in governing subsequent crystallization behavior. In particular, sinusoidal thermal modulation combined with high overheating temperatures (above ∼1275 K) markedly extends the supercooled liquid region, with reductions in crystallization temperature of up to 80 K. Our findings underscore the combined influence of microgravity, overheating temperature, and thermal modulation in controlling liquid-phase behavior and optimizing processing conditions for bulk metallic glass formation at large scales.