粗晶Ti40合金超塑性变形时的动态软化行为研究

The dynamic softening behavior of coarse-grained Ti40 alloy during superplastic deformation

摘要:

采用单向拉伸试验对粗晶Ti40合金进行了超塑性能测试，并结合TEM和EBSD分析技术研究了该合金超塑性变形过程中的动态软化行为及机制。结果表明：粗晶Ti40合金在所选实验条件下具有良好的超塑性能并在840oC、1×10-3s-1条件下获得最大延伸率436%；基于形变Z因子和断裂延伸率并结合微观组织分析可将变形条件划分为无超塑性、动态回复、动态再结晶三个区域；分别基于Sellars模型和KM方程建立了Ti40合金超塑性变形的动态再结晶临界应变模型和位错密度演变模型；粗晶Ti40合金超塑性变形过程中的动态回复以位错运动—位错胞—多边形化—形成亚晶的机制为主；动态再结晶机制主要为亚晶持续转动导致大角度晶界形成的连续动态再结晶。

Abstract:

The dynamic softening behavior of coarse-grained Ti40 alloy during superplastic deformation was studied by means of tensile tests as well as TEM observation and EBSD analysis. The results show that coarse-grained Ti40 alloy exhibits good superplasticity in most test condition and the maximum elongation 436% was obtained at the condition of 840oC, 1×10-3s-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 continous dynamic recrystallization resulting from the subgrains rotation leading to the formation of high-angle grain boundaries.