Microstructure Evolution and Composition Variation in Mushy Zone of Co-87.9wt%Sb Alloy under TGZM Effect

Based on TGZM (temperature gradient zone melting) effect, the Co-87.9wt%Sb alloy was melted followed by thermal stabilization for 20 min, 2 h, 4 h and quenching in a directional solidification apparatus. Then, the solidified phases and the composition distribution of the mushy zone were researched. The results show that under the temperature gradient, there exists a mushy zone between the complete liquid zone and the non-melted solid zone. Along the direction of the temperature gradient, the mushy zone of Co-87.9wt%Sb alloy is divided into three parts including CoSb₃+L, CoSb₂+L and CoSb+L. Due to TGZM effect, the volume fraction of the liquid phase in the mushy zone gradually decreases and the interface between the mushy zone and the complete liquid zone moves towards the low-temperature zone as thermal stabilization time increases. According to the composition distribution of the mushy zone, after thermal stabilization, the solute concentration obviously deviates from the initial concentration of Co-87.9wt%Sb alloy, which is smaller than that of the complete liquid zone. Theoretical analysis and computation explain the above experimental observations. After 4 h thermal stabilization, the volume fraction of CoSb₃ in CoSb₃+L of the mushy zone increases significantly up to 98.8%, indicating it is feasible to prepare CoSb₃ material via TGZM effect.