受损航空钛合金锻件局部结构连续点式锻压激光成形修复

To solve the practical problem that it is difficult for conventional laser forming repair technology to make the damaged aviation titanium alloy forgings to regain the mechanical properties which meet the requirements of aviation service condition, this project will combine laser forming repair technology and continuous point-forging, and establish a matching heat treatment regime. On the basis of in-depth study of microstructures evolution process and its evolution mechanism of the 'growth and repair titanium alloy material', stress formation law, and deformation behavior of titanium alloy forgings during continuous point-forging and laser forming repair process, acquiring the theoretical understanding of key physical metallurgy and material preparation science issues, stress formation mechanism and structural deformation mechanism during the process of the damaged titanium alloy forgings repaired by using continuous point-forging and laser forming repair technology, exploring a new repair technology that is able to achieve the consistency in internal microstructures and mechanical properties of the repaired titanium alloy forging, the mechanical properties of the repaired titanium alloy forging meeting the requirements of aviation service condition, and the deformation degree of the damaged titanium alloy forging being controlled during repair process, and optimizing the continuous point-forging and laser forming repair process window and the recrystallization heat treatment process condition, lay a solid basis of material preparation science and technology for high-quality reparation of the damaged large-scale complex titanium alloy forgings in planes and craft engines.

为解决常规激光成形修复技术难以使受损航空钛合金锻件重新获得满足航空服役条件要求的力学性能的实际问题，本项目将激光成形修复技术与连续点式锻压相结合，并建立相配套的再结晶热处理制度。在深入研究连续点式锻压激光成形修复过程"生长修复"钛合金材料显微组织形成过程及形成机制、应力形成规律、钛合金锻件变形行为的基础上，获得对受损航空钛合金锻件局部结构连续点式锻压激光成形修复过程关键物理冶金与材料制备科学问题、应力形成机理、结构变形机制的理论性认识，探索出能够实现修复钛合金锻件内部组织和力学性能一致、力学性能满足航空服役条件要求、修复钛合金锻件变形可控的新型受损航空钛合金锻件局部结构成形修复技术，并优化出连续点式锻压激光修复技术工艺窗口和再结晶热处理工艺条件，为飞机、航空发动机中受损大型复杂钛合金锻件的高质量修复奠定坚实的材料制备科学与技术基础。

本项目针对传统的激光成形修复技术难以使受损航空钛合金锻件重新获得满足航空服役环境条件要求的力学性能的实际难题，提出并建立了受损钛合金锻件连续点式锻压激光快速成形技术，该技术最突出的技术特点是：可激光增材制造出具有钛合金锻件组织和力学特征的钛合金零件；该技术另一个显著的技术特点是：有效消除了传统钛合金零件激光增材制造过程中由于热应力与残余应力交互作用导致的应力强度累积效应，保证了连续点式锻压激光增材制造钛合金零件的精确成形。本项目取得的重要结果如下：（1）建立了整套的具有自主知识产权的钛合金零件连续点式锻压激光快速成形工艺装备系统；（2）采用连续点式锻压激光快速成形技术制备了TC11、TA15钛合金厚壁零件，利用OM、SEM等手段研究了连续点式锻压激光快速成形TC11、TA15钛合金的组织和力学性能。结果表明，TC11钛合金试样内部的等轴晶晶粒尺寸均匀，平均晶粒尺寸～48.7μm。等轴晶的晶界α相连续，晶内是初生α相板条+β转变组织组成的双态组织。在连续点式锻压激光快速成形过程中，连续点式锻压时，TC11钛合金厚壁零件的表层变形区深度约为1.5 mm，变形量为20%。在连续点式锻压冷变形TC11钛合金上表面沉积新层过程中，当激光束扫描经过时，熔池热影响区中约1 mm厚(4层)冷变形TC11钛合金被加热到钛合金β转变温度之上，并在0.86 s内完成再结晶；（3）热处理结果表明，经α+β两相区热处理退火后，TA15钛合金试样内部等轴晶组织中连续的晶界α相发生断裂并球化，与此同时，等轴晶晶内的显微组织随退火温度升高按以下顺序转变：网篮组织→双态组织→等轴α+β组织。上述研究结果充分表明，通过选择连续点式锻压激光快速成形工艺参数和合适的热处理工艺制度，不仅可以对连续点式锻压激光快速成形的钛合金内部等轴组织的晶粒尺寸大小进行主动设计和控制，而且还可以对连续点式锻压激光快速成形钛合金等轴晶内部显微组织进行调整和优化，进一步设计和控制连续点式锻压激光快速成形钛合金的力学性能。