粗晶Ti40合金超塑性变形时的动态软化行为研究

The dynamic softening during superplastic deformation and its mechanism was studied by means of tensile tests, TEM observation and EBSD analysis for coarse-grained Ti40 alloy. The results show that the coarse-grained Ti40 alloy exhibits good superplasticity under the test conditions and the maximum elongation of 436% is obtained under the condition of 840℃, 1×10^-3 s^-1. The deformation conditions can be divided into three areas: none superplasticity area, dynamic recovery area and dynamic recrystallization area based on the Zener-Hollomon factor and elongation combined with the microstructure analysis. The critical strain model and dislocation density evolution model of dynamic recrystallization were established based on Sellars model and KM equation, respectively. The dynamic recovery mechanism is dominated by dislocation motion-dislocation cells-polygonization-subgrain formation, while the recrystallization mechanism is mainly the continuous dynamic recrystallization resulting from high-angle grain boundaries caused by the subgrains rotation.