Duplex Solidification Mechanisms of Glass Forming Zr₅₅Cu₃₀Al₁₀Ni₅ Alloy During Electromagnetic Levitation Processing

The liquid undercooling capability and rapid solidification kinetics of quaternary Zr₅₅Cu₃₀Al₁₀Ni₅ alloy were investigated by electromagnetic levitation technique. On the basis of molecular dynamics simulation for liquid thermophysical properties, the temperature field and fluid flow pattern during containerless processing were revealed through electromagnetic field analyses. In the small undercooling regime < 213 K, a multilayer onion-like structure was formed by containerless solidification, which consisted mainly of primary Zr₂Cu dendrites and ternary (Zr₂Cu + ZrCu + Cu₁₀Zr₇) eutectics. Once liquid undercooling exceeded 235 K and even attained 310 K (0.27 T_L), a duplex solidification mode involving the glass formation in core region and the normal crystallization at outer area was observed during levitation processing. This resulted in a composite morphology composed of amorphous core and crystalline shell. The coupled effects of radial undercooling gradient and sluggish primary phase growth were responsible for inducing such a complex solidification mechanism.