单晶薄壁构件增材制造修复微观蠕变性能及失效机理

Working in the environment of high temperature, high pressure and corrosion, the single crystal turbine blades become the consumable parts of aircraft engine. Due to high temperature and high speed rotation, creep becomes the dominant failure mode of single crystal turbine blades. The application of additive manufacturing (AM) technology on the repair of thermal thin wall structures can greatly reduce the maintenance cost of aircraft engine. So far, the creep properties of AM repaired single crystal thin wall structures have not been fully understood, which brings in difficulties in the evaluation of its strength and life. Since the volume of repair zone is limited with irregular geometries, conventional uniaxial tensile/compressive tests can not be carried out. Moreover, conventional tests in macroscale can not reflect the effect of micro-structure gradient on creep properties. Concerning over the microstructure characteristics, this project will be started by local micro-indentation creep tests to investigate the mechanism that how the micro-structure gradient influences creep properties of AM repaired single crystal thin wall structures. The micro-indentation creep mechanism will be revealed by observation and evolution analysis of microstructures. Taking the microstructure and micro-creep property gradient into account, the methodology of residual life evaluation of AM repaired single crystal thin wall structures will be proposed by building the relationship among microstructure, micro-creep properties and macro-creep properties, and verified by repaired in-service single crystal turbine blade. This project will provide important theory foundation for the application of AM technology on the repair of single crystal turbine blades.

单晶涡轮叶片处于高温、高压、腐蚀等复杂工作环境下，成为航空发动机易损件。在高温和高速旋转下，蠕变成为单晶涡轮叶片主要失效模式。增材制造应用于热端薄壁件的修复，可极大地节约发动机维护成本。目前对单晶薄壁构件增材制造修复蠕变性能研究较少，导致缺乏有效的强度与寿命评估方法。由于修复区体积较小且形状不规则，传统的单轴拉伸/压缩试验难以开展，且宏观试验无法反映微结构梯度对蠕变性能的影响。本项目围绕单晶薄壁构件增材制造修复微观组织结构特点，从局部微观压痕蠕变响应出发，通过微结构观察与演化分析，研究微结构梯度对修复件微观蠕变性能的影响，揭示微观蠕变变形及失效机理。考虑微结构和微观蠕变性能梯度，通过建立微结构、微观蠕变性能和宏观蠕变性能之间的联系，提出单晶薄壁构件增材制造修复剩余寿命评定方法，并通过单晶涡轮叶片工程修复件考核。本项目可为增材制造技术在单晶涡轮叶片修复中的应用提供重要理论参考和依据。

增材制造技术又被称为3D打印技术，现已广泛应用于国内外先进航空发动机涡轮部件的制造与修复。涡轮叶片做为航空发动机中的一种易损部件，其造价昂贵，采用增材制造技术对局部损伤的叶片进行修复，会有效降低叶片的维护成本。涡轮叶片长期在高温、高压的环境中服役，镍基单晶高温合金具有优异的高温力学性能，因此被广泛用于发动机涡轮叶片中。近年来，国内外学者对增材制造镍基高温合金工艺参数、微结构特征及其拉伸强度进行了研究，但对增材制造镍基单晶薄壁构件的蠕变性能的研究较少。本项目通过有限元法研究了不同扫描路径对增材制造修复件中温度场和应力场的影响。利用激光立体成形技术制备了增材制造修复镍基单晶薄壁构件，研究了增材制造修复镍基单晶薄壁构件的微观组织结构分布特征。考虑微结构和微观蠕变性能梯度，分析了镍基单晶薄壁修复件的局部压痕响应和循环蠕变寿命，揭示了修复件的循环蠕变性能及其失效机理。本项目可为增材制造技术在单晶涡轮叶片修复中的应用提供重要理论参考和依据。