细晶Ti2AlNb基合金制备机理及其热变形过程组织性能调控

As a class of novel and light high temperature structural material, Ti2AlNb-based alloy has been received considerable attentions and rapidly developed throughout the world because of its higher yield strength, fracture toughness, creep resistance and low coefficient of thermal expansion et al. However, when the traditional methods of casting and ingot metallurgy were employed to prepare this kind of material, a series of undesirable problems would happen, including the coarse microstructure, poor mechanical property and complicated deform processing et al, which limit the practical application. Thus it is fairly significant to refine the grain size of Ti2AlNb-based alloy to improve microstructure and enhance mechanical property. In the present investigation, the fine-grained Ti2AlNb-based alloy, which is characterized by the high compactness and fine-grained microstructure, will be prepared using the hydride approach of mechanical milling and hot-pressing sintering. In addition, the control of microstrucutre and property of the prepared material during hot deformation will be carried out. The main study research contents of this work contains the evolution mechanism of powder structure, densification behavior, microstructural evolution at elevated temperature et al. With the help of implement of the proposed research, it will build a solid foundation and provide the technical support for the preparation of high quality and fine-grained Ti2AlNb-based alloy and its improvement of hot working ability.

Ti2AlNb基合金具有较高的高温屈服强度、高断裂韧性、高蠕变抗力、低热膨胀系数等优点，成为当前国内外广泛关注和迅速发展起来的新型轻质高温结构材料。但采用传统铸造和铸锭冶金方法制备该材料会导致组织粗大不均匀，力学性能不理想，不能直接用来成形零部件以及成形工艺复杂等问题的发生，阻碍了其实用化进程。因此，细化Ti2AlNb基合金晶粒尺寸对改善该材料的显微组织及提高其力学性能具有重要意义。本项目采用机械球磨与热压固结相结合的方法制备具有高致密度及细晶组织的粉末冶金Ti2AlNb基合金，并实现所制备材料热加工过程组织性能调控。主要研究Ti2AlNb预合金粉末机械合金化过程中粉末结构、形貌及尺寸的演变机理，粉末体的致密行为以及坯料在热变形过程的显微组织演变规律及其与力学性能关系等内容。本项目的实施将为高质量细晶Ti2AlNb基合金的制备及其热加工性能的提高奠定理论基础并提供技术支持。

Ti2AlNb基合金由于具有较高的高温屈服强度、高断裂韧性、高蠕变抗力、低热膨胀系数、无磁性和阻燃性能好等优点，已成为目前国内外广泛关注的新型轻质高温结构材料。采用传统铸造和铸锭冶金方法制备该材料会引起组织粗大不均匀，力学性能不理想，不能直接用来成形零部件以及成形工艺复杂等问题，使该材料的工程化应用受到了限制。本研究基于粉末成形工艺的研究进展与现状分析，提出采用机械球磨与热压固结相结合的方法制备具有高致密度的粉末冶金Ti2AlNb基合金。.本研究通过机械球磨技术，研究了球磨工艺参数对粉末冶金Ti2AlNb基合金粉末晶粒尺寸的影响规律，基于人工智能技术建立了球磨工艺参数与粉末特征参量的神经网络关系模型，确定了最佳的机械球磨工艺。采用真空热压烧结工艺，制备了细晶、高性能的粉末冶金Ti2AlNb基合金。基于有限元模拟数值模拟技术，揭示了不同热压烧结条件对粉末体坯料致密度的影响。阐明了不同热压烧结温度对粉末冶金Ti-22Al-25Nb合金显微组织、相组成及含量、力学性能等方面的影响。研究了热压烧结试样中B2晶粒的热稳定性，揭示了不同等温热处理参数下显微组织的演变规律，建立了晶粒长大动力学模型。研究了该合金在高温变形过程的流动应力特征及其软化行为，建立了塑性变形本构关系模型。基于功率耗散理论，构建了三维热加工图，分析了Ti-22Al-25Nb合金在不同热加工区间内的热加工性能，优化了热加工工艺参数，并且采用二次开发技术，实现了热成形过程中热加工图重要参数在坯料内部分布与演变规律的动态可视化表征。.通过本项目的研究，确立了一条以机械球磨与真空热压固结相结合的方法制备具有高致密度、组织细小、成分均匀的粉末冶金Ti2AlNb基合金的实用化技术途径，解决了相关基础科学问题，突破了关键工艺技术难点，不仅为金属间化合物材料的工程实际应用奠定了理论基础，而且对推动此类材料向高端结构零件应用的发展具有重要意义