冲击拉伸载荷下两相钛合金的塑性变形机理研究

α+β titanium alloys have been of great importance in the military and civil fields due to their low weight and high strength. These alloys would be unavoidably subjected to extreme service conditions, i.e. high strain rate, high temperature, and large plastic strain et al..Accurate understanding of mechanical behavior and deformation mechanism of two-phase titanium alloy in the super-normal environment and load conditions is of great significance. A single stress pulse impact tension technique is used to conduct loading-unloading tests at different temperatures, plastic strains and strain rates. Deformation mechanism under the coupling condition of strain, temperature and strain rate is determined based on the micro- and macro- observation of freezing samples. A physically based crystal plasticity model of two-phase titanium alloy incorporating the dislocation slip and twinning mechanism is proposed. Based on the numerical modeling and analysis, it will uncover the influences of strain, temperature and strain rate on the mechanism and bridge the deformation mechanism evolution rules and mac-mechanical behavior. The expected results may provide deeper insights into the relationship between material structure and mechanical behavior, and also provide richer clues for the optimization design of titanium alloy. The relevant theory and method can also lay the research foundation of other structural material.

轻质高强的两相钛合金是军民领域内的重要材料，服役中不可避免地经历高应变率、高温、较大塑性变形等超常条件。因此深入理解两相钛合金在超常加载条件下的力学行为和变形机理具有重要意义。本项目拟采用单应力脉冲拉伸加卸载实验技术，对两相钛合金实施不同温度和应变率的冲击拉伸加卸载实验，并结合对“冻结”试样的微细观显微观察及分析，实验研究应变和温度、应变率等耦合条件作用下两相钛合金宏观力学行为的微细观变形机制；针对冲击载荷可能引起的孪生机制，建立同时计及位错滑移和孪生机制影响的两相钛合金晶体塑性多晶本构模型；基于上述本构模型，开展不同加载条件下的多晶数值分析，最终揭示两相钛合金变形机理演化规律与宏观力学行为的关联。通过以上研究，预期加深对两相钛合金材料结构-性能关系的认识，为两相钛合金（尤其是抗冲击型钛合金）的力学改性提供指导，所形成的本构理论和方法也可为其他结构材料的研究奠定基础。

本项目以军民领域内轻质高强的两相钛合金为对象，围绕该材料高应变率、宽温域、较大塑性变形等超常服役需求背景，解决宏观拉伸力学行为和微细观变形机理关联研究不充分等关键问题。首先，通过双重热处理工艺探索获得了具有双态组织结构的TC11钛合金，结合单应力脉冲拉伸加卸载实验技术、金相显微镜、扫描电镜等试验手段，获得了TC11钛合金的宏观拉伸应力应变行为和组织演化规律，揭示了力学行为的温度和应变率相关性；结果表明：初生和次生α相的比例受限于固溶温度，次生α相的厚度随冷却速率的提高而减小，材料中次生α晶片层厚度的减小会提高材料的屈服强度而略微降低失稳应变；不同于准静态加载情况，高应变率拉伸加载下材料早期失稳的原因是绝热温升，而非孔洞微裂纹；利用基于Zerilli-Armstrong（ZA）的修正模型，较好地表征了TC11拉伸力学行为的温度和应变率敏感特征。其次，基于经典热激活理论建立了滑移系初始临界切应力对温度的依赖关系，通过多晶体塑性分析，较好地模拟了TC11双态组织两相钛合金在213 K～573 K温度范围内的单向拉伸流动特性，一定程度上解释了合金元素浓度和次生α相尺寸对TC11力学性能的强化作用。研究成果加深了对两相钛合金材料结构-性能关系的认识，可为两相钛合金（尤其是耐温抗冲击型钛合金）的力学改性提供指导，所形成的本构理论和方法也可为其他结构材料的研究奠定基础。相关内容和成果已发表SCI论文2篇，中文期刊论文1篇，在审论文1篇，满足了项目拟定所有研究目标。