VAR熔炼TiAl铸锭的成分分布及显微偏析

 采用XRD、SEM和化学成分分析等方法,分析了VAR二次熔炼获得的Ti-46Al-2Cr-2Nb铸锭的成分分布、微观组织及显微偏析,研究了其形成的规律。结果表明,沿铸锭径向,Al元素在R/2处质量分数最高,边缘及中心质量分数较低,Cr元素由边缘向中心质量分数逐渐增多,Nb元素从铸锭边缘到中心质量分数逐渐减少；沿铸锭轴向,Al元素自底部到顶部质量分数逐渐降低,Cr元素分布遵循正偏析元素规律,Nb元素偏析规律与Al元素相似。铸锭大部分区域为由α₂+γ片层团及晶界处少量等轴状γ相组成的近全片层组织,在铸锭中心偏上的区域存在由(α₂+γ)片层团组成的全片层结构。铸锭中显微偏析主要存在于片层团交界处,其中Cr元素的显微偏析比较严重。

Composition Distribution and Microsegregation in TiAl Ingot by Using VAR Process

A Ti-46Al-2Cr-2Nb alloy ingot was prepared by the process of double vacuum arc melting. The composition distribution and microsegregation in Ti-46Al-2Cr-2Nb alloy were studied. The microstructure and phase composition of the alloy were investigated by means of back scattered electron imaging, X-ray diffraction, energy dispersive spectrometry, and chemical composition analysis. The main results in detail are as follows：In the transverse sections, the content of Al is at the highest level in the place of R/2, however, the content of Al is low on the edge and radial zone of the ingot. The content of Cr is increased and the content of Nb is gradually decreased from the fringe to the center of the ingot, respectively. Along the longitudinal sections, the content of Al is gradually decreased from the bottom to the top of the ingot, the distribution of Cr is following the law of positive segregation elements, and the segregation law of Nb is similar to that of the Al element. The microstructure of the ingot mainly consists of α₂ and γ phases. Most areas of the ingot are composed of α₂+γ lamellar groups and a small amount of equiaxed γ phases at the colony boundaries, what is called nearly fully lamellar. The areas in the centre of the upper part ingot have a full lamellar structure composed of α₂+γ phase. The microsegregation of the ingot exists around colony boundaries, where the microsegregation of Cr element is quite serious.