Al0.7CoCrFeNiCu0.5高熵合金的定向凝固组织演变规律

Microstructure Evolution of Al 0.7 CoCrFeNiCu 0.5 High Entropy Alloys During Directional Solidification

为探究Al0.7CoCrFeNiCu0.5高熵合金定向组织在不同抽拉速度下的微观组织演化规律,文中实验设置抽拉速度(v=1μm·s^-1、2μm·s^-1、3μm·s^-1、10μm·s^-1),采用真空电弧熔炼炉和高温度梯度定向凝固炉(温度梯度20K·mm-1)制备试样。利用扫描电镜及能谱仪表征定向组织固液界面以及宏微观组织演变。研究结果表明:试棒沿生长方向可以分为淬火区、固相区及固态相变区。随着抽拉速度增大,固液界面形貌演变过程为:平界面→胞状→树枝状,胞枝转变临界点约为2μm·s^-1。凝固组织与抽拉速度及界面形态密切相关,抽拉速度增大,微观组织定向特征增强。固液界面为树枝状时,Cu原子被排斥到枝晶间形成富Cu相。

The paper studies the evolution of the directional microstructure of Al 0.7 CoCrFeNiCu 0.5 high entropy alloys at different pulling velocities.The Al 0.7 CoCrFeNiCu 0.5 alloy was prepared by vacuum arc melting and the directional solidi cation(DS)technique at the pulling velocities of 1~10μm·s^-1.A scanning electron microscope and an energy spectrometer were used to characterize the evolution of its liquid/solid interface and microstructure.There are regions of quenching zone,solid phase zone,and solid phase transformation zone in the direction of crystal growth.With the pulling velocity increasing,the morphology of the solid/liquid interface elolves from flat to cell and to dendritic,and the critical point of cell branch transition was about 2μm·s^-1.The solidification microstructure is closely related to the pulling velocity and interface morphology.The microstructure orientation characteristics strengthens when the pulling velocity increases.Cu rich phase forms due to the fact that Cu atoms are repelled between the dendrites when the interface is dendritic.