Ti-V-Cr系阻燃钛合金大晶粒超塑性变形特性与变形机制研究

Superplastic forming technology is one of the most effective methods which can process the hard-forming materials. In order to resolve the difficulty of hot workability and grainboundaries cracking easily during the high temperature deformation of Ti-V-Cr burn resistant titanium alloys, considering the characteristic of Ti-V-Cr alloys with single large beta grains which is difficult to obtain superplasticity with refined grains, large-grained superplasticity of Ti-V-Cr alloys is proposed. The basic research is focus on the characteristic and the mechanism of large-grained superplastic deformation in this project. Firstly, the deformation characteristic of Ti-V-Cr alloys will be researched by tensile tests and the constitutive equation will be constructed. Then, based on the dynamic evolution of microstructure, the effect of thermodynamic parameter on the substructure variables will be discussed. The relationship between curvature change of grainboundaries and defects evolution will be established. The mechanism of continuous deformation in coordination during the large-grained superplastic deformation will be identified and the superplastic deformation mechanism of Ti-V-Cr alloys with large grains will be investigated. Based on the above results, the parameters of superplastic isothermal forging of Ti-V-Cr alloys will be designed and the forging characteristic of these alloys under superplastic state will be researched to explore the practicability of superplastic isothermal forging of titanium alloys with large grains. The results of this project can provide the theory basis on the hot workability improvement of Ti-V-Cr alloys and realizing the large-grained superplastic isothermal forging technology.

超塑性成形技术是加工难变形材料极为有效的方法之一。为解决Ti-V-Cr系阻燃钛合金热加工困难，高温变形晶界易开裂的问题，针对该系合金β晶粒粗大，难以实现细晶超塑性的特点，本项目提出研究Ti-V-Cr系阻燃钛合金的大晶粒超塑性，针对大晶粒超塑性变形的力学、组织特征和变形机制开展基础研究工作。采用单向静载拉伸试验研究Ti-V-Cr系阻燃钛合金大晶粒超塑性的变形行为，构建大晶粒超塑性状态方程。基于微观结构的动态演变规律，明确热力学参数对亚结构变量的影响，建立微观尺度晶界曲率变化与缺陷演变之间的关系，阐明大晶粒在超塑性变形时保持连续性的微观机理，揭示大晶粒超塑性变形机制。在此基础上设计Ti-V-Cr系阻燃钛合金超塑性等温锻造参数，研究该合金超塑性状态下的锻造特性，探索钛合金大晶粒超塑性等温锻造的可行性。研究结果可为改善Ti-V-Cr系阻燃钛合金的热加工性，实现大晶粒超塑性等温锻造技术提供理论依据。

本项目从解决Ti-V-Cr系阻燃钛合金热加工困难的实际问题入手，采用大晶粒超塑性变形的加工方法，系统研究了该系合金大晶粒超塑性变形的力学行为及组织特征，并探讨了大晶粒超塑性的变形机制。首先对由单向拉伸试验所获得的相关力学参量进行解析，确定了合金可实现大晶粒超塑性的变形区间，建立了基于热力参数的唯象型本构关系；结合粗大晶粒变形时的演变规律以及晶粒内部位错及亚结构特征，建立了动态再结晶临界应变模型及位错密度模型，明确了位错及亚结构在变形中的作用机理，揭示了大晶粒超塑性的变形机制。在此基础上，结合热模拟压缩试验，对超塑性等温锻造进行了评估。项目研究成果具有显著的科学意义及应用前景，对于改善Ti-V-Cr系阻燃钛合金的热加工性，实现大晶粒超塑性成形过程和质量的有效控制，促进钛合金大晶粒超塑性成形技术向工程化应用发展具有重要的理论价值。