航空发动机高温合金涡轮叶片增材制造/修复熔池流动稳定性与缺陷形成关联研究

One of the key challenges that constrains the high-performance laser additive manufacturing to mature applications in high-temperature components of aerospace engines, especially turbine buckets, is the quality consistency and micro-defects (pores and inclusions). Micro-defects are difficult to completely avoid during laser additive manufacturing process due to the molten pool disturbance and lack of external pressure. Defects are detrimental to fatigue performance and mechanical properties since they act as stress concentrators leading to an earlier onset of plasticity. Furthermore, the on-line monitoring and afterwards non-destructive testing methods are insufficient so the positions and distributions of defects are difficult to predict, which could seriously affect the serviceability of high-temperature components under actual load conditions..In response to the above problems, this project will focus on the morphology, classification, mechanism and control of defects during nickel-based super-alloy laser additive manufacturing and repairing process. Firstly, 2D/3D morphologies of additive manufacturing defects would be reconstructed by using synchrotron radiation method, the classification of high-temperature alloy laser additive manufacturing/repair defects would be summarized. Secondly, the on-line monitoring of melt pool temperature field, flow field and defect generation process during laser melting would be adopted. On the basis of the two-dimensional and three-dimensional morphologies, the melt pool instability and defect formation during laser melting are correlated to explore the formation mechanism of different types of defects. Thirdly, on the basis of the defect morphology, classification and considering the material properties along with the melt flow instabilities, optimized process parameters will be proposed to ensure the quality consistency and defects inhibiting.

制约高性能金属增材制造在航空发动机高温部件（尤其是转子部件）上成熟应用的关键难题之一是质量一致性和微缺陷控制。由于成形过程存在熔池扰动和缺少外部压力，微缺陷（气孔与夹杂）难以完全避免，出现位置难以预测，成形后无损检测手段和能力不足，严重影响高温部件在实际载荷环境下的使用可靠性。.本项目针对上述问题，开展缺陷形貌、分布与成形过程在线监控研究，期望从熔池稳定性的角度阐明缺陷形成机制和规律。一是采用先进缺陷分析和检测手段，获得内部缺陷的二维和三维形态特征，形成高温合金激光增材制造/修复缺陷分类说明；二是开展温度场、流场及缺陷产生过程实时观测与分析，在缺陷二维和三维形态研究的基础上，将成形过程中的熔池震荡、熔核不稳定与缺陷形成相关联，探索不同种类缺陷的形成机制；三是在缺陷形态、分类、机制研究的基础上，从材料物性和熔体流动稳定性出发，提出缺陷在线抑制和成形质量一致性保证的工艺措施。

针对航空发动机高温合金部件增材制造需求，采用GH4169（IN718）变形镍基高温合金和DD407铸造单晶镍基高温合金两种材料，以及粉末床激光熔融成形（PBF-L）和激光熔覆沉积（DED-L）两类工艺，实现叶片试制和修复。分析成形过程中可能出现的缺陷类型、特征和分布规律，进行科学分类；分析熔池动态行为和缺陷产生过程，进而与实际成形参数和条件相关联，阐明其形成机制；实现成形过程在线监测、工艺优化和缺陷抑制，提出成形质量一致性保证的工艺措施。.项目采用先进的缺陷/飞溅分析和检测方法，开展PBF-L成形“熔池飞溅与缺陷形成”关联研究。探究工艺参数对缺陷特征的影响，依据形貌特征对缺陷进行科学分类。通过提取熔池飞溅信息，分析飞溅行为对缺陷形成的影响机制，提出抑制缺陷的工艺措施；借助高速摄像和红外成像技术，开展DED-L成形“熔池行为-气孔缺陷”关联研究。清晰观察到熔池表面气泡演化与缺陷形成之间的关联，分析熔池表面流场、温度场等物理现象的时空演化规律，阐释气孔缺陷的内在形成机制，为抑制内部冶金缺陷、发展过程监控系统提供指导；基于低成本的光电探测器，建立熔池辐射信号与增材工艺参数的内在联系，提出异常工艺（缺陷产生）的识别判断准则和纠错调控方法，阐释了熔池辐射信号的基本物理内涵，探索出一种适合规模化应用的激光成形过程监控方式。.项目的研究获得了航空发动机材料增材制造/修复随机孔洞等缺陷（缺欠）的形貌特征和分布规律，揭示了熔池飞溅、流动和气泡演化等行为与缺陷形成的内在关联，提出了各类缺陷的形成机制和工艺优化方法，初步实现了成形过程在线监测和缺陷抑制，促进了金属激光成形在航空发动机中的实际应用。