(哈尔滨工业大学 材料科学与工程学院，哈尔滨 150001)
摘 要: 在一定的温度梯度下，采用Bridgman定向凝固炉对Ti-46Al-8Nb合金进行不同抽拉速度(3~70 μm/s)的定向凝固实验。研究定向凝固过程中的相变过程、微观组织以及微观偏析情况，并测量枝晶间距λ、层片间距λL和维氏硬度HV随凝固条件的变化规律。结果表明：在生长速度范围内，初生相为β相，凝固过程中发生包晶反应，最终得到α2/γ层片结构和B2相的组织。包晶反应导致较大的偏析，其中Al在枝晶间富集而Nb在枝晶心部富集。另外，随着生长速度的增加，枝晶间距以及层片间距逐渐减小，并且分别遵从λ=719.88v-0.21和λL=2.86v-0.25关系。而其维氏硬度随着生长速度的增加而增加，这是由于高的生长速度对应较大的过冷度，使层片组织细化，硬度值升高，其线性拟合函数式为HV=300.2v0.08。并将所得数据与先前的实验结果进行对比和分析。
关键字: 钛铝合金；定向凝固；微观组织；层片结构；硬度
（School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China）
Abstract:Ti-46Al-8Nb alloy was studied in directional solidification experiments at different growth rates (3-70 μm/s) using a Bridgman type directional solidification furnace at a constant temperature gradient. The phase transition, microstructure and microsegregation were investigated during the directional solidification, and the evolution of cellular spacing (λ), lamellar spacing (λL) and Vickers hardness with the growth rate were measured. The results show that, at the selected growth rates the growth of primary β phase accompanied with the peritectic reaction is observed, and the final microstructure is composed of a2/g lamellar structure and B2 phase. The peritectic reaction leads to the distribution of solute inhomogeneous severely, in which Al is rich in the interdendritic region and Nb is rich in the core of the dendrite. Additionally it is obtained that the cellular spacing and the lamellar spacing decreased with the increase of the growth rate in the selected growth rates according to the relationship of λ=719.88v-0.21 and λL=2.86v-0.25, respectively. While the values of Vickers hardness HV increase with the increase of the growth rate according to the relationship of HV=300.2v0.08, which could be attributed to the fined lamellar structure due to the high undercooling. The results obtained above were compared with the previous results in this work.
Key words: TiAl-based alloy; directional solidification; microstructure; lamellar structure; hardness
