高强韧近β钛合金在大塑性变形过程中的超细晶形成及增韧调控机制

High-strength and toughness near β titanium alloy, such as Ti-55511, is a kind of important aircraft structural material. It has become one of the research hotpots in the field of titanium alloys, because of its ability to replace the high-strength steel to achieve the remarkable weight reduction. The further improvement of mechanical strength can be achieved by the fabrication of ultra-fine microstructure using severe plastic deformation. However, it has some problems about the deformation resistance and fracture failure. And the investigations of the related micro-mechanism are also absent. In this project, the SPD of high-strength and toughness near β titanium alloy will be carried out by introducing the concept of the design and control of initial microstructure and process microstructure. And the formation of ultra-fine microstructure and its toughening will be investigated systematically. By considering the peculiarities of this kind of titanium alloy, such as the complex interface evolution, the following mechanisms can be revealed: 1) the launch, development and interaction of dislocation and twinning and their control mechanism under the action of complex interface evolution, 2) the formation and separation patterns of the α and β substructures under the interaction between dislocation and twinning, and 3) the control mechanism about the interface stability and twinning characteristic in the ultra-fine microstructure for toughening. Then, the relationships between the initial microstructure and SPD conditions and the deformation resistance, effect of microstructure refining, twinning characteristic and interface stability can be established. Sequentially, according to the mechanical tests and fracture analysis, the optimized microstructure for toughening and the corresponding SDP control can be ascertained. Finally, the theoretical foundation about the fabrication of ultra-fine microstructure titanium alloys can be further enriched and improved, and the related new technology prototype can be established.

Ti-55511等高强韧近β钛合金是一类重要的航空结构材料，能够取代高强钢、获得显著减重，成为钛合金领域的研究热点。采用大塑性变形（SPD）对该类钛合金进行超细晶制备，能够进一步提升力学强度，但在变形抗力、断裂失效等方面存在难点和问题，相关微观机制研究较为缺乏。本项目基于“初始组织和过程组织设计调控”的思想，对该类钛合金实施SPD，并系统研究其中的超细晶形成及增韧调控机制：针对其界面演化复杂等特点，重点揭示在复杂界面演化作用下的位错和孪晶启动、发展和交互机制及调控机理，在位错和孪晶交互作用下的α和β亚结构形成-分离模式，以及针对超细晶增韧的组织界面稳定性调控和孪晶特征调控机理；构建初始组织、SPD条件与变形抗力、晶粒细化效果、孪晶特征、组织界面稳定性之间的相关性；根据力学性能和断裂分析，明确增韧所需满足的超细晶特征及SPD调控手段；进一步丰富钛合金超细晶制备的理论依据，并建立其新技术原型。

以Ti-55511为代表的高强韧近β钛合金是一类重要的航空结构材料，能够取代高强钢、获得显著减重，成为钛合金领域的研究热点。采用大塑性变形（SPD）对该类钛合金进行超细晶制备，能够进一步提升力学强度，但在变形抗力、断裂失效等方面存在难点和问题，相关微观机制研究较为缺乏。.本项目系统研究近β钛合金中的超细晶形成及增韧调控机制： （1）通过热压缩实验研究Ti-55511合金在变形温度973-1123K、应变速率0.01-10s-1条件下的流变行为。采用应变补偿Arrhenius(SCA)和反向传播人工神经网络(BPANN)方法对该热变形过程本构关系进行建模，并通过统计分析和交叉验证对模型进行评估。将两种模型扩展的应力应变数据植入有限元，仿真热压缩实验过程；（2）基于跨相区双道次热压缩试验，研究了Ti-55511合金跨相区双道次流变行为，分析了Ti-55511合金不同预变形温度下组织演变规律，揭示了两相区预变形温度对Ti-55511钛合金单相区退火再结晶的影响规律；（3）以单向热轧为变形方式，研究不同初始组织的Ti-55511合金在热变形条件下的组织及性能演变。揭示了热轧条件下α相与β相的变形机制，研究了α相与β相演变对性能的影响，分析了亚稳相及亚结构的形成条件与原因。为近β钛合金的热变形行为及组织性能调控提供理论及实验依据；（4）对比性研究单向、交叉轧制对Ti-55511合金组织结构及力学性能的影响。研究交叉轧制下组织细化机制，揭示交叉轧制对合金织构及各向异性的影响。以此为交叉轧制作为近β钛合金特殊的变形方式提供理论及实验依据。..在项目执行期间，发表了高水平学术论文20篇，其中SCI收录20篇；申请国家发明专利1项，已授权1项；获得省部级奖励2项；培养了博士研究生4名，硕士研究生3名。