激光区熔定向凝固Gd5Ge4合金的相选择与组织特征

对具有包晶反应的Gd5Ge4金属间化合物进行激光区熔快速定向凝固实验,研究了Gd基磁致冷材料激光快速定向凝固过程中的相选择机制和显微组织特征.结果表明,激光区熔快速定向凝固后的Gd5Ge4合金具有明显的择优取向,合金在激光快凝条件下同时发生非晶化现象.GdsGe4合金定向凝固组织的片层间距随激光扫描速率的增加而减小,合金的凝固组织特征和激光扫描速率的关系符合J-H模型.

Phase Selection and Microstructure Characteristics of Directionally Solidified Gd5Ge4 Alloy by Laser Zone Re-melting

The Gd5Ge4 alloy with the peritectic reaction during solidification was prepared by the arc-melt method under protection of argon atmosphere.The as-cast alloys were cut and directionally solidified with the help of laser rapid solidification technique.Microstructure characteristics and phase selection of Gd5Ge4 during the rapid directional solidification by laser zone re-melting were investigated.The microstructure originating from steady-state growth was evaluated with the help of optical microscope (OM) and X-ray diffraction (XRD).The alloy after laser zone directional solidification possesses obvious preferred orientation and the amorphization occurs under this condition.The cellular spacing could be expressed as a function of the laser scanning velocity during the rapid solidification.An acceptable combination is found between the experimental results and the classical J-H numerical solidification model for a rapid cellular/dendritic growth.