TiNb基合金的β稳定性与单晶剪切模量C44的内在相关性研究

Elastic modulus is an important mechanical parameter to evaluate biomedical titanium alloys, and the mechanism of low modulus in β titanium alloys has been always a key academic issue in the field of biomedical materials and advanced titanium alloys. It is well known that the elastic modulus of β titanium alloy is dominantly controlled by single-crystal shear modulus C’. However, our recent experimental study indicated that the single-crystal shear modulus C44 could exert significant influence on elastic modulus. This is helpful to understand the relationship between β-phase stability and elastic modulus, and might provide a novel approach to the design of low modulus titanium alloys. In this project, the influence of thermo-mechanical treatment on microstructure and mechanical behavior will be systematically studied to fabricate β TiNb-based alloys with ultralow elastic modulus. Based on the above work, the single-crystal elastic constants will be extracted from polycrystalline specimen by using an in-situ synchrotron X-ray diffraction technique to investigate the influence of β-stabilizing element content and temperature on the single-crystal elastic property, and the intrinsic correlation between β-phase stability and C44 will be revealed, and the physical mechanism of the realization of ultralow elastic modulus in β titanium alloys will be illustrated. This will lay a theoretical foundation for the design and development of novel β titanium alloys.

弹性模量是考量生物医用钛合金的重要力学性能指标，β钛合金的低模量机制已经成为当前生物医用材料和先进钛合金领域的关键科学问题。通常认为，β钛合金的弹性模量取决于单晶剪切模量C’。我们在前期研究中发现，单晶剪切模量C44也可对弹性模量产生重要影响。这将有助于理解β钛合金的结构稳定性与弹性模量的关系，并为低模量钛合金的设计提供新思路。本项目拟以TiNb基β钛合金为研究对象，系统研究热机械处理对微观组织和力学行为的影响规律，设计制备具有超低弹性模量的合金。在此基础上，采用同步辐射技术从多晶样品中“抽取”材料的单晶弹性常数，研究β稳定元素含量和温度变化对单晶弹性性能的影响规律，揭示β相结构稳定性与C44的内在相关性，阐明β钛合金实现超低弹性模量的物理机制，为新型β钛合金的设计与研发奠定理论基础。

亚稳β钛合金凭借其良好的耐蚀性、优异的生物相容性以及高强度和低模量等，在生物医用植入件领域具有重要的应有背景。杨氏模量是生物医用钛合金的一个关键力学性能指标，降低弹性模量可以减少应力屏蔽效应，进而增强其力学相容性。本项目以TiNb基β钛合金为研究对象，系统研究成分和热机械处理对材料微观组织、相组成和力学性能的影响规律，设计制备据具有较低弹性模量的Ti39Nb合金和Ti31Nb3Zr4Sn（wt.%）合金，合金模量分别为39 GPa和31 GPa，具有一定的应用前景。利用原位同步辐射实验研究低模量合金在加载过程中的相变行为，发现通过热机械处理获得的近单一β相组织相对于β+α”双相组织具有更高的诱发马氏体相变临界应力，因此具有更好的屈服性能。合适的退火处理对实现高强度和低模量的匹配至关重要。利用弹塑性自洽模型结合同步辐射技术，从多晶样品中抽取合金的单晶弹性常数，发现两种低模量合金不但具有较低的剪切模量C’还具有较低的剪切模量C44，两者共同贡献了合金的低模量，低模量合金的两种剪切模量都与稳定性密切相关。基于上述结果，本研究提出选取合适低稳定性的合金，通过热机械处理引入缺陷降低马氏体相变点，将β相保留至室温获得低稳定性合金，从而可以通过同时降低C’和C44获取低模量钛合金。本研究阐明了合金实现低模量的机制并提出低模量合金设计的一般准则，对于开发和设计新型低模量钛合金具有重要科学意义。