TGZM效应下Co-87.9%Sb合金糊状区的组织演化及成分变化

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

以TGZM(temperature gradient zone melting)效应为理论基础,将Co-87.9%Sb(质量分数,下同)合金置于定向凝固设备中加热熔化,在一定温度梯度下分别保温20 min,2 h,4 h后淬火,对其糊状区的凝固组织和成分分布进行了研究。结果表明:在一定温度梯度下,介乎于完全液相区和未熔固相区之间存在着固/液相共存的糊状区,Co-87.9%Sb合金的糊状区沿温度梯度方向分为CoSb_3+L,CoSb_2+L以及CoSb+L 3层;在TGZM效应作用下,随着保温时间的增加,糊状区内液相体积分数逐渐减少,糊状区与完全液相区界面向低温区移动;经保温处理后,由EDS获得的糊状区成分分布表明,糊状区内的溶质浓度明显偏离合金初始浓度,完全液相区溶质浓度高于初始值;通过理论分析与计算解释了上述现象。经过4 h保温处理后,糊状区CoSb_3+L部分中的CoSb_3含量大幅增加,在该部分高温端甚至可达98.8%,表明借助TGZM效应经过长时间保温制备CoSb_3热电材料的方法是可行的。

Based on TGZM（temperature gradient zone melting） effect, the Co-87.9 wt%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-87.9 wt%Sb alloy is divided into three parts including CoSb_3＋L, CoSb_2＋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-87.9 wt%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 CoSb_3 in CoSb_3＋L of the mushy zone increases significantly up to 98.8%, indicating it is feasible to prepare CoSb_3 material via TGZM effect.