等径角挤压诱发TiNi基合金中第二相回溶及与晶粒细化关系研究

The present applicant previously found that the effect of second phase on the microstructure of TiNi-based alloys processed by equal channel angular pressing (ECAP) is related to the type of second phase. It should be emphasized that dissolution of Ti3Ni4 phase can be caused by ECAP and significantly promotes the grain refinement of TiNi-based alloy. We proposed that this is related to the interaction between dislocation and second phase under a thermal-mechanical coupling condition. Therefore, the present project selects the different TiNi-based alloys with different second phases and investigates microstructural evolution of ECAP-processed TiNi-based alloys, and illustrates the mechanism of dissolution of second phase by considering the combined effect of the interaction between second phase and dislocation in matrix and that between second phase and dislocation in itself. Secondly, the relationship between dissolution of second phase and grain refinement is revealed. The emphasis was placed on understanding the relationship among the segregation of solutes, tangled dislocations and grain refinement to reveal the microstructural mechanism of the effect of dissolution of on grain refinement. In the last part, effect of second phase on martensitic transformation and shape recovery properties of ECAP-processed TiNi-based alloys is investigated and the mechanism behind is revealed. This may provide the new way to develop the TiNi-based alloys with high strength, high shape recovery properties and excellent irradiation resistance. The related results also enrich the theory of grain refinement induced by plastic deformation and provide helpful experiences for development of other high strength alloys.

申请人前期发现不同类型的第二相对等径角挤压TiNi基合金显微组织的影响存在极大差异。值得关注的是，等径角挤压诱发Ti3Ni4相回溶，并且回溶能够显著促进合金晶粒细化。我们认为这与热力耦合作用下位错等缺陷与第二相之间的交互作用有关。因此，本项目选择具有不同第二相特征的TiNi基合金，研究等径角挤压TiNi基合金微观组织演化规律，分析第二相与基体内位错、第二相内位错之间的交互作用，阐明第二相回溶的微观本质；明确第二相回溶与晶粒细化之间的关系，分析溶质原子偏聚、位错缠结与晶粒细化之间的内在联系，揭示第二相回溶对等径角挤压TiNi基合金晶粒细化影响的微观机制。研究第二相回溶对等径角挤压 TiNi基合金马氏体相变与形状记忆特性的影响机制，为发展具有高强度、高恢复特性与良好耐辐照能力的 TiNi基合金提供新思路。相关研究成果还将丰富塑性变形导致晶粒细化的理论，为发展其他高强合金体系提供借鉴。

以等径角挤压和高压扭转为代表的大塑性变形工艺以及冷轧、冷拔等传统的塑性变形工艺制备的超细晶TiNi基合金受到研究者的广泛重视。塑性变形导致的材料微观组织变化，如晶粒细化、非晶化等很大程度上受初始材料内第二相的影响，进而影响材料的马氏体相变与形状恢复特性。因此，本项目的目的在于系统研究等径角挤压诱发的TiNi基合金中第二相回溶及其与晶粒细化关系、对马氏体相变与形状恢复特性的影响与机制。.本项目选择具有不同第二相特征的TiNi基合金作为研究对象，首先研究了等径角挤压TiNi基合金的微观组织演化规律，分析了位错在第二相回溶中的作用，阐明了第二相回溶的微观本质，分析了其热力学机制，确定了单道次挤压条件下，第二相回溶的临界尺寸；其次，建立了第二相回溶与等径角挤压后合金晶粒尺寸之间的关系，揭示了第二相回溶影响晶粒细化的微观机制；第三，系统研究了第二相回溶对等径角挤压TiNi基合金马氏体相变特征的影响规律，结合微观组织分析，分析了等径角挤压TiNi基合金马氏体相变的影响因素与机制，提出了第二相回溶影响多步马氏体相变的模型；最后，研究了等径角挤压TiNi基合金的力学行为与形状恢复特性，分析了其影响因素，阐明了第二相回溶影响TiNi基合金形状恢复特性的机理。通过本项目的研究，成功揭示了等径角挤压诱发TiNi基合金中第二相回溶的微观机理，建立了第二相回溶与晶粒细化之间的关系，丰富了塑性变形导致晶粒细化的理论，明确了第二相回溶对TiNi基合金马氏体相变与形状恢复特性影响的本质，为进一步研发高强高形状恢复特性的TiNi基合金部件提供理论依据。