不同应变率下高氧含量钛的力学行为及失效机制研究

Titanium and its alloys are widely studied and used in areas such as aeronautics, aerospace and oil industry, because of their promising properties including high specific strength, good corrosion resistance and excellent creep resistance. Also, owing to the outstanding biocompatibility of titanium, they are also known and actually widely-used as medical implant materials. However, in recent years, clinic research on Ti alloys used for medical implants revealed that most of the alloying elements put into Ti, especially the rare earth and noble elements, are potentially harmful to human health. Therefore, development of commercially pure Ti with high oxygen content was proposed and has been made a great progress. Nevertheless, there has been no research being carried out in regards of mechanical behavior, deformation mechanisms and failure manner of the Ti-O binary alloys at various loading rates. For the purpose of boosting the application process of the alloys in industries, research works from various aspects are urgent to be performed for them. To this end, we propose to investigate the relationship among the microstructures, mechanical behavior and failure manner of the alloys at different strain rates, and also to explore the rule of microstructural evolution under loading, as well as the effect of oxygen solid solution on the deformation mechanism, strain rate sensitivity and constitutive relationship of the alloys. In addition to a solid theory in understanding the micro/macro-mechanics and reliability of the Ti-O binary alloys, we will provide a criterion to evaluate the failure and service life of these materials in application.

钛及钛合金材料具有轻质高强、抗腐蚀、抗蠕变以及良好的生物相容性等特点，因此不仅在航空航天和石油勘探等领域得到广泛的应用与关注，而且也是生物医学领域最受欢迎的植入体材料。近年来，在开发不掺杂贵、重金属合金的高性能钛合金方面，利用高氧含量固溶的高强韧钛-氧二元合金取得了一定进展。然而，对该类材料在准静态、动态等不同应变率加载下的力学行为、变形机理以及断裂失效机制等的研究几乎还是一片空白，亟待开展相关研究以便推进工程应用领域的研究与评估。本项目拟通过对该类材料在不同应变率加载环境下的微观组织演变过程、力学表现行为以及断裂失效方式等三者之间的研究，揭示氧固溶原子含量对钛及钛合金塑性变形机理、应变率效应以及本构关系的影响；并建立高氧钛及钛合金材料的失效预测判据，为该类材料在宏/微观力学性能、服役寿命预估以及可靠性等工程应用研究提供坚实的基础理论。

钛及钛合金材料因轻质、高强韧等力学性能和良好的防腐蚀性能在航空航天、医疗器械、体育运动以及石油勘探和零配件等领域具有广泛的应用。但是直到最近，钛的昂贵成本一直是钛合金使用的主要障碍，并且钛合金中使用稀有元素进一步加剧了这种现象。而氧作为一种高效的间隙元素，可以有效解决这些问题。同时，由于钛合金强度对氧含量极为敏感，氧原子能够显著提高钛合金的硬度、强度，但超过一定含量时将剧烈地降低合金的塑性、断裂韧性。但是本项目申请人克服了这一矛盾，经过特定工艺制备出高强高韧高氧含量的纯钛材料。但是目前这类材料的研究处于起步阶段，对该类材料在多环境变量加载下的系统研究（包括但不限于在准静态、动态等不同应变率加载下的力学行为、变形机理以及断裂失效机制等）几乎还是一片空白。本项目研究了该类材料在不同应变率单轴加载环境下的力学响应及其破坏行为，并结合微观表征试验的结果发现，氧原子导致密排六方晶格常数比值c/a单调增大，对材料的晶粒尺寸、织构几乎没有影响。另外，氧除了对材料的强化作用外，氧含量的增加还导致了材料绝热剪切破坏倾向的增加。对加载后高氧钛的显微组织检测发现，高氧钛绝热剪切带中发生了明显的相变，且绝热剪切带中的纳米晶由母晶相变而来，即α→β→α相变过程参与了ASB的演化。同时，本项目开展了氧对单一<a>型柱面滑移系的影响的研究，揭示了氧对钛的微观力学性能的影响，结果表明，氧含量对<a>型柱面滑移系的激活几乎没有影响，但显著降低了单晶微柱的应变率敏感性。该项目的研究结果是对氧原子对材料力学响应影响机制的进一步完善，是对绝热剪切带传统再结晶晶粒细化机制的重要补充，并为完善动态冲击载荷下的绝热剪切演化机制提供了重要理论支撑。