单晶叶片基体表面微裂纹成因分析

单晶高温合金是制造先进航空发动机涡轮叶片的主要材料，其优异性能主要来源于消除了与主应力轴垂直的晶界，而 单晶材料中如果出现再结晶会显著降低其高温力学性能。为探究发动机单晶涡轮导向叶片试验后在叶身前缘下缘板R区产生裂 纹的原因，利用视频显微镜、金相显微镜和扫描电镜等手段对裂纹截面组织进行宏、微观分析，明确了R区的宏观裂纹为抗氧化涂 层裂纹，宏观裂纹附近的叶片基体存在由于叶片表面胞状再结晶晶界开裂所引起的微裂纹。结果表明：单晶叶片表面产生胞状再 结晶主要与叶片抛光、吹砂等修整过程中引入的塑性变形及后续的钎焊工艺有关；抗氧化涂层的开裂促进了胞状晶晶界的开裂； 通过对导向叶片的多个截面组织进行对比分析，发现高温能够加速胞状再结晶的晶界开裂。

Microcracks Analysis of Matrix Surface of Single Crystal Blade

The excellent mechanical properties of single crystal superalloys mainly result from the elimination of grain boundaries per? pendicular to the principal stress axis, which is the main material for manufacturing advanced aeroengine turbine blades. However, if re? crystallization occurs in single crystal materials, its high-temperature mechanical properties will be significantly reduced. In order to inves? tigate the causes of the cracks in the R region of the hub side endwall near the leading edge of the single crystal turbine guide vane after the test, the crack sections were analyzed by macro and micro analysis utilizing video microscope, metalloscope, and SEM. It was found that the macroscopic cracks in the R region were anti-oxidation coating cracks, and there were microcracks in the blade matrix near the macroscop? ic cracks caused by the cracking of cellular recrystallization grain boundaries on the blade surface. The results show that cellular recrystalli? zation on the surface of single crystal blades is mainly related to the plastic deformation introduced in the dressing process such as polish? ing, sandblasting and the subsequent brazing process. The cracking of the anti-oxidation coating promoted the matrix cracking of the cellu? lar recrystallization grain boundary. Through comparative analysis of multiple cross-section metallographic structures of the guide vane, it was found that high temperature can accelerate the cracking of the cellular recrystallization grain boundary.