βTi-Mo合金孪生/滑移耦合变形机制及性能优化

Based on the unique phenomenon of plastic deformation that {332}<113> twinning results in low yield strength and large uniform elongation, while dislocation slip leads to high yield strength and negligible uniform elongation in beta titanium-molybdenum alloys, a proposal is put forward for introducing the couple of two deformation modes, namely twinning and slip, into the same material. To explore the mechanism of twinning /slip coupled deformation and the approach of twinning/slip coupled strength-ductility, two kinds of composites will be fabricated for controlling the couple of twinning /slip deformation modes on a large scale: one is the lamilated macro-composite by using the twinning-type alloy and the slip-type alloy; the other is the mechanical twins and omega phase combined micro-composite by using the twinning-type alloy. The evolution of deformation microstructures including twins and dislocations in these composites will be elucidated comprehensively during the twinning/slip coupled deformation, and the interactions of deformation microstructures with interface and omega phase will be clarified by the detailed microstructure analyses. The correlations between the flow stress of coupled deformation and the microstructures such as twins, dislocations, interface and omega phase will be established quantitatively or semi-quantitatively. The mechanism of twinning/slip coupled deformation and the effective approach of twinning/slip coupled strength-ductility will be revealed. Through a combination of two methods of strengthening and toughening, namely the twinning/slip coupled deformation and the traditional microstructure control, the mechanical properties will be optimized for the practical requirement due to the controlled deformation modes and microstructures. Efforts of this study will provide a complement for not only the theory of plastic deformation but also the theory of strengthening and toughening, which serve as the theoretical guides and technical supports for the development of advanced beta titanium alloys.

基于βTi-Mo合金以{332}<113>孪生方式变形时屈服强度低和均匀延伸率高，而以位错滑移方式变形时屈服强度高和均匀延伸率低的独特塑性变形现象，提出在同一材料中引入孪生与滑移两种变形方式耦合的设想。为探索孪生/滑移耦合变形机制及耦合强韧化途径，制备孪生型与滑移型合金多层交替的宏观复合材料以及孪生型合金中机械孪晶与ω相组合的微观复合材料，大范围内调控孪生/滑移变形方式的耦合。观察分析孪生/滑移耦合方式变形过程中孪晶和位错组织的演化规律以及变形组织与界面及ω相之间的交互作用，定量或半定量描述耦合变形流变应力与孪晶、位错、界面及第二相的关系，揭示孪生/滑移变形方式的耦合机制及耦合强韧化效果。通过孪生/滑移方式耦合强韧化和传统的组织控制强韧化相结合，控制多因素组合，实现合金性能的目标优化设计。本项目研究将丰富和发展晶体塑性变形理论与材料强韧化理论，为发展高性能β钛合金提供理论依据和技术支撑。

利用Ti-Mo基合金以{332}<113>孪生方式主导变形时屈服强度低和均匀延伸率高，而以位错滑移方式变形时屈服强度高和均匀延伸率低的独特塑性变形现象，成功制备出具有孪生与滑移耦合变形方式的机械孪晶与ω相组合的微观复合材料、以及孪生型与滑移型合金多层交替的宏观复合材料，并获得了良好的屈服强度和均匀延伸率匹配。阐明了合金中变形孪晶数量随晶粒尺寸减少而减少的变形方式的晶粒尺度效应，以及孪生变体及其对塑性变形贡献的晶粒取向依赖性。基于孪生变形导致孪晶不断分割晶粒产生的动态晶粒细化效应，揭示了变形过程中位错平均自由行程先急剧后平缓减少，而位错密度逐渐增加的演变规律。明晰了等温ω相的析出行为基本不受预变形组织孪晶和位错的影响，以及层界面的存在抑制了孪生与位错滑移在晶内的传递行为。建立了流变应力与变形组织孪晶和位错之间的关系式，阐明了塑性变形初期的应变硬化行为主要归功于孪生引起的动态霍尔-佩奇效应，这对晶体塑性变形理论起到了一定的补充和扩展。通过孪生与滑移变形方式双重耦合，及其与传统的固溶强化、细晶强化、析出强化的多重耦合，实现了在较大范围内对合金的强塑性调控，这为发展高强塑β型钛合金提供了一定的理论基础和技术支撑。