脉冲电流辅助多向扭转锻造制备超细晶/纳米晶Ti2AlNb合金及其变形机理研究

With the increasing demand for lightweight in the aerospace field, the novel structural-materials with lightweight and high-temperature resistant such as Ti2AlNb alloys need to be widely used. Microstructure optimization based on grain refinement is regarded as an effective way to obtain the high-performance Ti2AlNb alloys. However, it is difficult to obtain the sufficient strain accumulation by traditional processes to meet the requirement of grain refinement. In this study, Ti2AlNb alloys prepared by elemental powder metallurgy are selected as the starting materials. The novel process of pulse current assisted multidirectional torsion forging is designed to fabricate the bulk ultra-fine/nanocrystalline Ti2AlNb alloys. Firstly, microstructure evolution under pulse current will be analyzed, the flow stress constitutive model coupling with pulse current will be established and the electroplasticity mechanism will be revealed systematically. Subsequently, the formation mechanism of ultra-fine/nanocrystalline Ti2AlNb alloy in pulse current assisted deformation will be explained. Besides, the in-situ microstructure adjustment of the ultra-fine/nanocrystalline Ti2AlNb alloy will be carried out and the effect of pulse current on dynamic behavior of microstructure will be analyzed. Furtherly, the hot workability of the ultra-fine/nanocrystalline Ti2AlNb alloy will be evaluated. Finally, the lightweight and high-temperature fastening bolts will be fabricated as typical components, which will provide theoretical foundation for the deformation technology and development of ultra-fine/nanocrystalline Ti2AlNb alloy parts with excellent properties.

随着航空航天领域关键装备轻量化需求的日益增加，Ti2AlNb合金等新型轻质耐高温结构材料亟待得到更广泛地应用。基于晶粒细化实现组织优化被认为是获取高性能Ti2AlNb合金的有效途径，而传统塑变工艺难以满足晶粒细化所需的大塑变累积。本项目以粉末冶金Ti2AlNb合金为研究对象，提出脉冲电流辅助多向扭转锻造制备块体超细晶/纳米晶Ti2AlNb合金的新工艺。系统分析脉冲电流辅助变形过程中的组织演变规律，构建脉冲电流耦合的流变应力模型，阐明电致塑性机制；揭示脉冲电流作用下超细晶/纳米晶形成机制；对制备的超细晶/纳米晶Ti2AlNb合金进行原位组织调控，揭示脉冲电流对其微观结构动态行为的作用机制，并对其热加工性进行评价；最终，以轻质耐高温紧固螺栓为典型构件进行试验验证，为合理确定超细晶/纳米晶Ti2AlNb合金塑性加工工艺和发展性能优异的超细晶/纳米晶零部件奠定理论基础。

随着航空航天领域关键装备轻量化需求的日益增加，Ti2AlNb合金等新型轻质耐高温结构材料亟待得到更广泛的应用。基于此，本项针对Ti2AlNb合金所面临的塑性变形能力差、变形温度高、设备条件苛刻等颈问题，深入研究了Ti2AlNb合金电流辅助变形机制，开展了如下工作：（1）研究了Ti2AlNb合金的电流辅助加热规律，得到了Ti2AlNb合金电流辅助下目标温度与电流之间T=1.3I+230℃；（2）构建了脉冲电流条件下Ti2AlNb合金本构模型，解耦了电场下的激活能；（3）阐述了Ti2AlNb合金电致塑性机制，电流促进位错滑移，抑制位错缠结，提高塑性；（四）揭示了Ti2AlNb合金剪应力变形机理，电场促进原子迁移，再结晶形核，晶粒细化；（五）研究了脉冲电流原位热处理对变形组织的影响规律及（六）超细晶Ti2AlNb合金热处理组织演变研究。总体上，Ti2AlNb合金脉冲电流辅助变形过程中合金变形能力提高与电流影响合金微观结构动态行为（微观组织形貌、相转变、位错运动、原子扩散等）密切相关，这为难变形材料塑性加工奠定了理论基础。