Thermophysical properties and solidification behavior of liquid Vit106a in microgravity.

Understanding thermophysical properties such as surface tension (σ), total hemispherical emissivity (ε), specific heat capacity (cp) and viscosity (η) as a function of temperature is essential for optimizing the vitrification of bulk metallic glasses (BMGs). In this study, the thermophysical properties of liquid Vit106a were measured aboard the International Space Station (ISS) using the electromagnetic levitator (EML). The surface tension σ exhibited a similar value with other Zr-based BMG, with a weak temperature dependence described by σ(T) = 1.557-4.36 ×10-5 × (T - 1106) N.m-1. The viscosity temperature-dependence η(T) was analyzed using the Vogel-Fulcher-Tammann (VFT) equation, yielding a kinetic fragility parameter of D* = 9.8 at high temperature, compared to D* = 21.6 at low temperature, that indicates a fragile-to-strong transition characteristic of Zr-based metallic glass formers. XRD analysis confirms full crystallization of the sample, despite being cooled at a rate of 16 K.s⁻¹, over nine times faster than the critical cooling rate of 1.75 K.s⁻¹ reported in the literature. The crystallized sample reveals a heterogeneous distribution of binary intermetallic phases, including ZrAl3, Zr2Cu, Zr2Ni, ZrAl and Nb2Ni. These findings provide insights into the thermophysical behavior of liquid Vit106a for large-scale manufacturing but also raise important questions regarding its good glass-forming ability for larger casting thickness.