高强β钛合金的α变体形变各向异性及强度预测模型

Precipitate strengthening has been always an effective strategy for enhancing strength of β-titanium alloys. Disclosing the intrinsic deformation and strengthening mechanisms of the precipitate phase is crucial for thoroughly understanding and accurately predicting mechanical properties of these high-strength titanium alloys. However, the research on this issue has been yet insufficient due to the difficulties in characterizing the elaborative deformation behaviors of α-variants. In this project, a typical high strength β-titanium alloy, i.e., Ti-10V-2Fe-3Al, will be chosen as a model material and the super-refined α-particles will be produced from β-matrix by means of the novel “pseudo-spinodal decomposition” process. The deformation and strengthening mechanism of the super-refined α-variants will be systematically studied using the micro-/nano-fabrication and testing techniques involving Focused Ion Beam (FIB) and Nanoindenter XP. The research will be performed as follows: (1) the different interactions between β-matrix dislocations and each α-variant, especially the deformation response of α-variants encountered by different deformation modes of β-matrix will be revealed; (2) the physics of the specific deformation path of α-variants will be elucidated by constructing both the atomic lattice model and energy landscapes from the first-principles calculation; (3) the intrinsic relationship among “α-variants, deforming and strengthening” will be disclosed. The assessment criteria of strengthening effect of α-variants will be created and a quantitative strength prediction model of β-titanium alloys, in which the deformation anisotropies of α-variants is taken as a crucial parameter, will be established. These results would be not only beneficial to understanding the fundamental deformation behavior of titanium alloys, but also provide with the experimental data and theory support to develop high-strength titanium alloys with much better reliability and performance.

析出强化是高强β钛合金的主要强化手段，深入揭示析出相的精细变形特性及强化效应对于准确理解、预测和设计钛合金高强性能至关重要。本项目以Ti-10V-2Fe-3Alβ钛合金为模型材料，通过“伪调幅分解工艺”析出超细α颗粒，采用微纳加工测试技术并结合第一性原理计算，系统研究β钛合金中α变体的形变特性及强化效应：(1)分析α颗粒与β基体位错的交互作用，揭示α变体的形变各向异性，阐明β基体各变形模式下α变体的变形响应规律；(2)结合晶体点阵分析和第一性原理计算，构建α变体形变原子尺度的点阵模型和能量图谱，透彻理解特定变形路径的物理成因；(3)厘清合金“析出相变体-形变-强化”的关联规律，建立α变体强化效应的评定准则，发展基于析出相变体形变各向异性的合金强度表征预测模型。通过以上研究，从理论上深入理解钛合金的基础变形行为，为组织调控、材料强化、发展高强钛合金提供实验依据和理论指导。

亚稳β钛合金中丰富相变诱导的结构强化赋予了合金高强度，而充分认识第二相的组织特征、变形行为以及对合金性能的影响是设计微观结构、挖掘强度潜力、实现合金高性能化的前提和基础。本项目针对亚稳β钛合金中第二相的精细结构、变形特征及其对合金形变、损伤、断裂及力学性能的影响进行了系统深入地研究，取得以下四方面重要研究结果：（1）研究了钛合金中ω第二相介导的韧脆转变的内在机理及物理起源。我们发现，普遍存在的钛合金“ω脆化”现象涉及等温ω粒子的“自硬化”，这种自硬化进一步被揭示为在原子结构上向稳定态的调整以及化学成分上β稳定化的原子扩散，结构和成分上的这两方面改变最终增加了原子结合键中的共价键倾向。（2）研究了高错配钛合金中“ω致脆”的形变、损伤、断裂特征及其机理。结果发现，合金在低温短时时效即可发生脆化，在微观结构上显示为严重局域化的变形带，同时在变形带个别位置发展出本质上具有“类非晶结构”的白斑。这些变形形貌仍归结为时效引起ω相成分结构变化导致的共价键倾向增加。（3）研究了增加高强β钛合金塑性的α相均匀化析出的策略。我们将合金热轧棒材进行适度固溶处理，尽量保持β相的锻造结构而不发生完全再结晶，利用组织中残留的位错缺陷改变α相的时效析出行为。结果发现，α析出相极为均匀细小，合金拉伸强度高达1670MPa，并获得超过5%的可观塑性。（4）研究了基于新结构的低成本高强韧钛合金开发。我们提出了采用化学界面工程制造纳米马氏体的新策略，同时结合元素扩散特性进行成分筛选，使得合金维持低成本并获得优异的强塑性匹配。这些研究结果丰富了钛合金形变的基础知识，为钛合金结构设计及强韧化提供一定的理论支撑。在项目资助下，在Nature Communications、Acta Materialia等国内外期刊上发表学术论文15篇，获得国家发明专利授权1项，参加学术会议并作特邀报告5次，培养研究生3名。