Chen Zhanxing, Ding Hongsheng, Chen Ruirun, Guo Jingjie, Fu Hengzhi
National Key Laboratory for Precision Hot Processing of Metals, School of Materials Science and Engineering, Harbin Institute of Technology, Harbin, 150001, China.
Sci Rep. 2019 Apr 2;9(1):5518. doi: 10.1038/s41598-019-41881-z.
In this article, microstructural evolution during the solidification of Ti-48Al-2Cr-2Nb with current density, as well as the formation mechanisms, are discussed, along with the impacts on microhardness and hot compression properties. The applied electric current promotes the solidification from the α primary phase to a largely β solidification in Ti-48Al-2Cr-2Nb. With an increase in supercooling, the solidification process have a tendency to change from an α-led primary phase to (α + β)-led primary phase. The primary dendrites, grain size, and lamellar spacing show a tendency to decrease first before increasing with increasing current density. Microhardness and high-temperature yield strength increase with a decrease in primary dendrite spacing, grain size, and lamellar spacing. Correlations between primary dendrite spacing, lamellar spacing, microhardness, yield strength, and current density are described by a fitting formula. An increase of α phase, due to the application of electric current, results in improved microhardness. The yield strength of Ti-48Al-2Cr-2Nb alloy increases linearly with microhardness. Yield stress increases with a decrease in microstructure parameters, in accordance with the Hall-Petch equation. The predominant modification mechanism with electric current application for TiAl solidification is the variation of supercooling and temperature gradients ahead of the mush zone due to Joule heating.
本文讨论了电流作用下Ti-48Al-2Cr-2Nb凝固过程中的微观结构演变及其形成机制，以及对显微硬度和热压缩性能的影响。施加的电流促进了Ti-48Al-2Cr-2Nb从α初生相凝固转变为主要的β凝固。随着过冷度的增加，凝固过程有从以α为主的初生相转变为以(α + β)为主的初生相的趋势。初生枝晶、晶粒尺寸和片层间距随电流密度增加呈现先减小后增大的趋势。显微硬度和高温屈服强度随初生枝晶间距、晶粒尺寸和片层间距的减小而增加。通过拟合公式描述了初生枝晶间距、片层间距、显微硬度、屈服强度和电流密度之间的相关性。由于施加电流导致α相增加，从而提高了显微硬度。Ti-48Al-2Cr-2Nb合金的屈服强度随显微硬度呈线性增加。根据霍尔-佩奇方程，屈服应力随微观结构参数的减小而增加。电流作用下TiAl凝固的主要变质机制是由于焦耳热导致糊状区前方过冷度和温度梯度的变化。
