β钛合金的马氏体相变与力学行为的相关性研究

Because of the important role of martensitic transformation played in the improvement of mechanical properties of materials and the realization of functional performance, the relationship between the martensitic transformation and the mechanical behavior has been a key issue in materials science and engineering. It was found in recent experimental study that the martensitic transformation in TiNb based β Ti alloys is closely related to their mechanical behavior, especially the strength and the elastic modulus. By athermal martensitic transformation and stress induced martensitic transformation as well as proper thermo-mechanical treatment, the β Ti alloys could gain high strength and low elastic modulus. This provides a novel approach to the design of advanced β Ti alloys with high strength and low modulus. It is of academic importance to clarify the relative mechanism, and of engineering significance to develop novel Ti alloys with high elasticity and the Ti alloys with low modulus. The aim of the present study is to clarify the relationship between the structural stability, martensitic transformation and the mechanical properties of TiNb based β Ti alloys, and to determine the effect of martensitic transformation, precipitation and microstructure on the mechanical behavior. In addition, in the present study the influence of martensitic transformation, precipitation and microstructural evolution on the mechanical properties of TiNb based β Ti alloys will be concerned, in attempt to discover the origin for the relation of martensitic transformation and mechanical behavior. The achievements of the present project will expand and deepen the study of martensitic transformation in β Ti alloys, laying a basis for designing and developing advanced Ti alloys.

由于马氏体相变在改善材料力学性能和实现功能特性方面的重要作用，马氏体相变与力学行为的关系一直是材料科学与工程领域的关键问题。我们在近期的实验研究中发现，TiNb系β钛合金中的马氏体相变与合金的力学行为，特别是与合金的强度和弹性模量具有高度相关性；通过热诱发和应力诱发马氏体相变并辅以热-机械处理，可使β钛合金兼具高强度和低（或超低）弹性模量，这为新型高强低弹模β钛合金设计提供了新思路。阐明与此相关的物理机制具有很高的学术价值，对研发具有重要应用前景的低弹模钛合金和高弹性钛合金具有指导意义。本项目旨在以TiNb系β钛合金为研究对象，弄清楚β钛合金的结构稳定性、马氏体相变与合金力学行为之间的相关性，研究马氏体相变、析出相变和微观组织演变对TiNb系亚稳β钛合金的力学性能的影响规律，揭示马氏体相变和力学行为相关性的内在机制，丰富和深化β钛合金中的马氏体相变研究，为新型β钛合金设计和研发奠定基础。

制备出了具有不同β稳定性的TiNb系β钛合金，并对其成分、相变及微观组织及力学性能进行分析和表征，确定了合金的结构稳定性与马氏体相变对TiNb系β钛合金力学行为的影响规律。深入研究了热－机械处理对TiNb系β钛合金微观组织演变的影响，结果表明，亚稳β钛合金的处理状态与合金的微结构及β相的结构稳定性高度相关，从而显著影响合金的力学行为，如强度和弹性模量。研究中我们采用剧烈冷轧和短时时效的方法，获得了具有超低弹性模量的TiNbSn亚稳β钛合金，揭示了合金在获得高强度的同时具有超低弹性模量的物理机制，即：具有低结构稳定性的合金如果在降温过程中不发生马氏体相变，那么合金的弹性模量则随着温度的下降而降低，从而使得合金在室温获得超低弹性模量。在此基础上，提出了低弹模和高强度兼备的β型钛合金的设计准则：适度降低钛合金中β稳定化元素含量，然后对合金辅以冷轧和短时时效处理引入的大量位错和晶界以提高β相的结构稳定性，同时利用冷轧和短时时效处理后合金中析出的细小α强化相对位错运动的阻碍作用，从而实现低弹模甚至超低弹模钛合金的设计。利用该设计原则，本研究结合当前TiNb系生物医用钛合金的热点和前沿，将马氏体相变与力学行为相关性研究成果扩展到其他TiNb系高强低弹性模量合金设计，并制备了兼具高强度和低弹性模量的TiNbSn、TiNbMoSn、TiNbZr和TiNbZrSn等亚稳β钛合金。本研究结合马氏体相变与力学行为的相关性，阐明了高强度和低弹性模量的物理机制，丰富和深化β钛合金中的马氏体相变研究，为新型β钛合金设计和研发奠定了基础。