具有TRIP/TWIP效应的高强高塑性β钛合金制备及其形变机理研究

Titanium and its alloys have been extensively used in numerous application fields. However, both their low ductility and their lack of work-hardening when compared with steels or Co-Cr alloys, limit their use in advanced applications where superior combinations of strength and ductility are required. As a consequence, it is necessary to develop new Ti-alloys with combination of high strength, large ductility and a high work-hardening rate. Therefore, inspired from the superior mechanical properties of TRIP/TWIP steels (TRIP for Transformation Induced Plasticity and TWIP for Twinning Induced Plasticity), we proposed a new type of metastable β Ti-alloys showing combined TRIP/TWIP effects through controlling the β stability of Ti-alloys. The alloys were designed based on the “d-electron alloy design method” and controlling of electron/atom ratio (e/a). The detailed microstructural analysis was performed to understand the deformation process. Various mechanisms, mechanical twinning and stress-induced phase transformation, were identified after mechanical testing, resulting in a complex network of deformed microstructures with very special synergetic features. Moreover, the relation between dislocations and new interfaces of deformation products were analyzed. Detailed analysis of above results showed that the novel approach can be explored in guiding the alloy-design, aiming to develop new metastable β Ti-alloys with high strength, large ductility and a high work-hardening rate thanks to combined TRIP and TWIP effects.

钛合金与不锈钢或Co-Cr合金相比具有两大明显缺陷：低塑性和差的加工硬化行为，这将会限制其在高强和高塑性环境下的应用和发展。针对这两大缺陷，本项目将不锈钢中的TRIP/TWIP效应应用于β钛合金，采用d-电子设计方法和控制合金电子浓度(e/a)的策略，通过控制合金的β稳定性，设计具有高强、高塑性和良好加工硬化能力的TRIP/TWIP效应亚稳β钛合金。研究所设计合金的TRIP/TWIP行为，探讨合金在均匀塑性变形过程中的结构演化规律，揭示变形产物（包括应力诱发相变和机械孪晶等）的产生机制，分析应变导致的相变界面和挛晶界面等新界面与位错的关系，建立结构演变的物理模型，明确TRIP/TWIP效应β钛合金设计准则，使该理论在指导合金设计过程中对合金性能和组织能做到可控、可靠、可优化，以期为发展具有高强高塑性的β钛合金探索一个新的方向。

本项目借鉴不锈钢中的TRIP/TWIP效应，利用d-电子设计方法和控制合金电子浓度(e/a)策略，通过添加适量的合金化元素，调控合金的β稳定性，设计出了TRIP/TWIP效应的钛合金：Ti-xV(x=15,16-22)、Ti-16V-4Sn、Ti-12Mo-5Zr、Ti-12Mo-10Zr和Ti-18Zr-13Mo等。单轴拉伸试验结果表明该系列合金具有高强、高塑性和良好的加工硬化性能。采用XRD、SEM-EBSD、TEM/HRTEM、ACOM TEM 等表征手段分析了该系列合金试样在塑性变形过程中的结构特征，研究所设计合金的组织演化过程，揭示变形产物的产生机制，分析变形过程中所产生的新界面与位错的关系，建立结构演变的物理模型。分析了不同类型合金化元素（比如Zr-Mo，V-Sn等）耦合作用对TRIP/TWIP效应的钛合金在塑性变形过程中所产生TRIP/TWIP效应的影响机制。研究合金设计参数（Bo，Md和e/a等）与组织、性能之间的关系，优化了TRIP/TWIP效应亚稳β钛合金设计理论。并在国际学术期刊上发表SCI论文11篇，它引超过60次，授权专利2项，培养研究生4名。