Homogenization of a metallic melt: Enhancing the thermal stability of glassy metal

Abstract

Molding and thermoplastic processing of metallic glasses rely on using a homogenized state of the melt or supercooled liquid (structure inherited from the melt). To homogenize metallic melts, however, reaching the liquidus temperature is not sufficient, and the upper temperature for quenching is often chosen empirically. Here, it is proved experimentally via fast scanning calorimetry that the homogenization temperature of a prototyped Au-based metallic melt lies 192 K above its liquidus temperature of 663 K. The homogenized metallic melt has enhanced resistance to phase transformations, better thermal stability and improved glass-forming ability. The existence of a high-temperature miscibility gap, below which the melt spinodally decomposes, is the origin of a homogeneous-to-inhomogeneous crossover upon cooling the melt. When the initial quenching temperature is above a critical temperature delineating the existence of the miscibility gap and a high cooling rate is applied, the homogeneous melt structure is preserved in the metallic glass. Consequently, the glass shows suppressed crystallization on reheating. The enhanced thermal stability of the supercooled liquid promises practical engineering applications such as in thermoplastic forming, additive manufacturing or welding. The present study not only evidences the existence of a high-temperature miscibility gap in the multicomponent glass-forming alloy but also offers an alternative route to improve the thermal properties of metallic glasses for engineering applications.