亚稳β钛合金应力时效行为及变体选择晶体学机制研究

Metastable β titanium alloys are important bearing structural materials for aeronautical applications due to their excellent mechanical properties. The dynamic evolution of microstructure under the coupling process of stress loading and aging precipitation has become a hot science issue. It is also the key of accurate control of microstructure and performance optimization of titanium alloys. However, the stress aging behavior of titanium alloys is not completely clear, especially the variant selection mechanism. The present project combines In-/Ex-situ characterization methods and crystallographic calculations to elucidate the alloying elements diffusion mechanism in metastable titanium alloys under different stress loading states, reveal the precipitation behavior and crystallographic variant selection mechanism of ω phase and α phase, establish the precipitation kinetics model of ω phase and α phase under stress aging condition, quantitatively characterize the relationship between stress aging technology-microstructure characteristics-mechanical property, and reveal the damage-fracture mechanism. The results can enrich the solid state transformation theory of metastable β titanium alloy and further develop the basic research of the phase transformation crystallography of titanium alloy. It can also provide a novel way for strengthening and toughening of metastable β titanium alloy. The study has great theoretical significance and engineering application value to the precise control and optimization of microstructure-property in thermomechanical processes.

亚稳β钛合金由于其优异的力学性能而成为航空工业应用领域重要的承力结构材料。近年来钛合金在应力加载与时效析出过程耦合作用下的微观组织动态演化规律成为热点科学问题，也是实现其组织精确调控和性能优化的关键，而目前关于钛合金应力时效行为的研究尤其是变体选择机制研究还不完全清楚。本项目将In-/Ex-situ表征手段以及晶体学计算等方法相结合，阐明亚稳β钛合金在不同应力加载方式下合金元素扩散机制，揭示不同应力加载方式对ω相及α相形核析出规律及变体选择晶体学机制，建立应力时效条件下ω相及α相析出动力学模型，定量表征应力时效工艺-微观组织特征-力学性能关系，揭示应力时效组织变性损伤断裂机理。研究结果不仅可以丰富亚稳β钛合金固态相变理论，进一步发展钛合金相变晶体学的基础研究，而且可为此类合金强韧化提供新的途径，对实现该类钛合金热成型过程中的组织-性能精确调控和优化具有重要的理论意义和工程应用价值。

亚稳β钛合金由于其优异的力学性能而成为航空工业应用领域重要的承力结构材料。近年来钛合金在应力加载与时效析出过程耦合作用下的微观组织动态演化规律成为热点科学问题，也是实现其组织精确调控和性能优化的关键。本项目以新型亚稳β钛合金Ti-7Mo-3Nb-3Cr-3Al（Ti-7333）作为研究对象，阐明了Ti-7333合金在等温应力时效、变温应力时效以及预变形时效等不同处理方式下ω相及α相析出演变规律，揭示了不同应力加载方式对ω相及α相变体选择的晶体学机制，掌握了应力时效条件下ω相及α相析出动力学特征，定量表征了应力时效工艺-显微组织特征-力学性能关系，探明了亚稳β钛合金应力时效组织变形损伤断裂机理，丰富和发展了亚稳β钛合金相变晶体学理论，为亚稳β钛合金组织性能调控和优化提供科学的理论依据。研究结果表明，施加弹性应力或室温预变形可以显著影响ω相及α相析出动力学特征，根据工艺参数条件不同抑制或促进相变发生；在此过程中发生强烈的变体选择效应，析出相变体种类具有典型的应力敏感性；外加弹性应力通过改变析出相与β基体的晶格常数，进而影响相界面特征，改变α相的析出及生长机制；预变形应力诱发马氏体同样存在变体选择效应且对后续时效α相析出产生决定性影响；不同时效工艺后合金组织变形、损伤、断裂机理显著不同。研究成果共发表学术论文15篇，其中SCI论文14篇；培养博士研究生3名，硕士研究生3名；申请国家发明专利4项，其中授权2项；获得2020年度陕西高等学校科学技术奖励一等奖（项目负责人排名第三）；参加学术会议7人次并作口头报告，获优秀报告奖2次。