定向凝固Ti-46Al-8Nb合金的微观组织演变与微观偏析

摘要

Directional solidification experiments were conducted for Ti-46Ak-8Nb alloy at the growth rates ranging from 3 to 70μm/s.The microstructure evolution and microsegregation pattern were investigated.In the range of growth rate,a regular dendritic structure appears and the primary dendrite spacing decreases with increasing growth rate.The peritectic reaction is observed during the solidification and the final microstructure is composed of α2/γlamellar structure and retained β(B2) after directional solidification.The lamellar orientation is found to be parallel and 45° to the primary growth direction ofβ dendrite.Peritectic reaction leads to significant chemical inhomogeneity,in which aluminum is rich in interdendritic liquid and niobium is rich in the core ofβ dendrite during the solidification.With the nucleation and growth of α phase,the segregation amplitude of niobium increases,which promotes the formation of B2 phase,while aluminum rich in the interdendritic becomes homogeneous gradually.%在3～70μm/s的生长速度范围内对Ti-46Al-8Nb(摩尔分数,％)合金进行定向凝固实验,研究其微观组织演变和微观偏析形式.在该生长速度范围内,固-液界面表现为规则的枝晶生长,一次枝晶间距随着生长速度的加快而逐渐减小.在定向凝固过程中观察到典型的L+β→α包晶反应,最终得到具有α2/γ层片和B2相的微观组织.在各个晶粒中,层片与β相枝晶初始生长方向呈0或45°.包晶反应导致严重的成分偏析,在凝固过程中,铝富集在枝晶间,铌富集在枝晶心部.随着α相的形核和生长,铌的偏析程度逐渐增大,从而促进B2相的析出,而富集在枝晶间的铝在包晶反应发生后逐渐变得均匀、一致.