预变形对钛合金两相区冷却过程中次生α相形核的影响

The synchronous and precise control of primary α phase and secondary α phase not only plays a key role to optimize the mechanical properties, but also be a serious problem in the heat treatment during the α+β phase region of titanium alloy. The investigation about the effect of pre-deformation on the nucleation of secondary α phase in the α+β phase region of titanium alloy can help to solve this serious problem. Firstly, this project will investigate the effect of pre-deformation on the content, grain size, orientation relationship and crystal defect of primary α phase and β phase. Secondly, the macro effect of pre-deformation on the morphology, content and grain size of secondary α phase well be investigated. Thirdly, based on the examination and analysis of the orientation relationship among the secondary α phase, primary α phase and β phase, the nucleation site and its selected criteria of secondary α phase will be investigated. Finally, based on the synthetical analysis of the previous results, this project will investigate the influencing micro-mechanism of pre-deformation on the nucleation of secondary α phase. This project would improve the solid phase transformation theory of titanium alloy depending on the progress in crystallography criteria for the nucleation of secondary α phase. Meanwhile, this project would benefit the development of precise control of microstructure, which lays the theoretical foundation for the design and new development of process for the heat treatment of titanium alloy.

同步、精细化调控钛合金初生α相和次生α相的组织状态，不仅是优化其力学性能的关键，也是钛合金两相区热处理领域的一大难题。预变形可调控次生α相的形核过程，进而调控次生α相和初生α相的组织状态。因此，研究预变形对钛合金两相区冷却过程中次生α相形核的影响具有一定的工程和科学意义。本项目首先研究预变形对初生α相和β相含量、晶粒尺寸、位向关系和晶体缺陷等组织状态的影响；其次，研究预变形影响次生α相几何形貌、含量和晶粒尺寸的宏观规律；然后，通过分析次生α相、初生α相和β相三者之间的位向关系，研究次生α相的形核位置、以及形核位置的选择准则；最后，综合分析预变形对次生α相形核影响的微观机制。本项目一方面有望在钛合金次生α相形核的晶体学条件方面取得新进展，完善钛合金固态相变理论；另一方面为钛合金热处理制度的制定和新工艺的开发奠定理论基础，促进钛合金微观组织精细化调控技术的发展。

钛合金双态组织由于具有良好的综合性能，因此备受关注。双态组织中，初生α相和次生α相的同步、精细化调控是优化其力学性能的关键，也是钛合金两相区热处理领域的一大难题。预变形可调控次生α相的形核过程，进而调控次生α相和初生α相的组织状态。因此，研究预变形对钛合金两相区冷却过程中次生α相形核的影响具有一定的工程和科学意义。.本项目提出通过预变形调控初生α相和β相的组织状态，从而调控次生α相的析出条件，进而实现初生α相和次生α相的同步、精细化调控。研究发现：（1）钛合金等轴组织高温变形过程中，β相承担了大量的塑性变形，容易发生动态再结晶。应变速率增大会促进初生α相的动态再结晶的发生，但是过高和过低的温度都会抑制动态再结晶的发生。（2）钛合金双态组织高温变形过程中，次生α相和初生α相之间存在变形不均匀性，且不同形貌的α相的分布也会使得不同区域的β相具有变形不均匀性。（3）钛合金轧制退火过程中，初生α相的再结晶机制为连续再结晶，而β相为晶界合并长大机制。这使得随着退火温度的升高，初生α晶粒尺寸先减小后增大，而β相晶粒尺寸逐渐增大。（4）钛合金冷却过程中初生α相长大和次生α相析出之间存在竞争关系，冷却速度和保温温度对这种竞争行为影响显著。（5）预变形在β相中产生大量位错时，次生α相将从片层状向等轴状转变。.本项目共发表学术论文8篇，其中SCI论文6篇。研究成果一方面在钛合金次生α相形核的晶体学条件方面取得了新进展；另一方面为钛合金热处理制度的制定和新工艺的开发奠定了理论基础，可促进钛合金微观组织精细化调控技术的发展。