超声冲击辅助激光快速成形Ti2AlNb基合金开裂控制及组织性能调控研究

Ti2AlNb-based alloy is one kind of key structural materials potentially used under 650~750℃ for aerospace. Laser melting deposition process demonstrates its outstanding advantages in technology and cost in fabricating components of Ti2AlNb-based alloy. But some problems such as cracking tendency and performance degradation due to the coarse microstructure should be resolved urgently. This project aims to control the cracking, microstructure and performance of laser melting deposited Ti2AlNb-based alloy through ultrasonic impact treatment process, which can refine materials microstructure obviously and form residual compressive stress. The finite element model for stress field analysis during laser melting deposition Ti2AlNb-based alloy assisted by ultrasonic impact treatment will be established. The formation, evolution of stress and mechanism of cracking control during the process will be analyzed. The refinement effect of ultrasonic impact treatment for laser melting deposited Ti2AlNb-based alloy will be analyzed based on the microscopic theory of plasticity and recrystallization theory. Based on above, study on microstructure and performance adjustment by heat treatment and mechanical behavior of laser melting deposited Ti2AlNb-based alloy assisted by ultrasonic impact treatment will be carried out. This work will lay a foundation of theory and technology for promoting the development and application of laser melting deposited Ti2AlNb-based alloy.

Ti2AlNb基合金是650~750℃下使用的最具潜力的航空航天结构材料之一，采用激光快速成形技术制造Ti2AlNb基合金结构件具有显著的技术及成本优势，但急需解决成形件易开裂及组织粗大导致性能下降的问题。项目充分利用超声冲击处理能显著细化材料组织并产生压应力的技术特性，提出开展超声冲击辅助激光快速成形Ti2AlNb基合金的开裂控制及组织性能调控研究，通过建立超声冲击辅助激光快速成形Ti2AlNb基合金的应力场有限元模型，分析超声冲击处理激光快速成形Ti2AlNb基合金过程中应力产生、演化及开裂控制机理；采用细观塑性理论及再结晶理论分析超声冲击处理对激光快速成形Ti2AlNb基合金的组织细化作用，在此基础上，开展超声冲击辅助激光快速成形Ti2AlNb基合金的热处理组织性能调控及力学行为研究，项目研究将为促进激光快速成形Ti2AlNb基合金的发展及应用奠定理论及技术基础。

Ti2AlNb基合金是650~750℃下使用的最具潜力的航空航天结构材料之一，采用激光增材制造Ti2AlNb基合金结构件具有显著的技术及成本优势，但急需解决成形件易.开裂及组织粗大导致性能下降的问题。项目深入研究了激光增材制造Ti2AlNb基合金凝固组织形成规律，并通过温度场模拟解释了沉积态薄壁试样底部材料发生固态相变的机理，分析了激光增材制造Ti-22Al-25Nb合金在不同相区热处理时的相变规律，设计了预处理+固溶时效和直接固溶时效两种热处理制度，对比分析了不同热处理制度对组织和性能的影响规律，薄壁试样经920℃/2 h/AC+800℃/24 h/AC热处理后，性能提升明显，水平方向底部和顶部室温抗拉强度分别达到了999 MPa、953 MPa，断后伸长率分别为6.0%、5.3%；采用间接耦合法，对激光增材制造成形和冷却过程中的应力场进行模拟分析，得出通过减缓散热有效控制成形和冷却过程中的应力水平，避免开裂发生；开展了激光增材TC11/Ti2AlNb、TA15/Ti2AlNb双合金界面及组织性能调控研究，项目研究为激光增材制造Ti2AlNb基合金的发展及应用奠定了理论及技术基础。..及应用奠定理论及技术基础。