This study deals with the investigation of failure mechanism of turbine guide vane and the oxide composition on the surface of failure vane cracks. The material of vane is Co-based superalloy DZ40M, which has directional solidified grain structure. The investigate methods include optical microscope (OM) observation, scanning electron microscopy (SEM) observation and energy dispersive X-ray spectrometry (EDS) analysis. The results of crack morphology observation show that: the cracks are distributed at almost all the rows of cooling holes at the middle of the vane and most macroscopic morphology of cracks are transverse propagation (perpendicular to directional solidification direction). Due to the high temperature environment and action of cycle thermal stress during service, the recrystallization tissue near the cooling holes which produced by high-energy laser production process can easily become the starting point of cracks. And the cracks propagate along the grain boundaries and sub-boundaries as the large difference of thermal expansion coefficient between carbides and matrix in high temperature. The results of oxide composition analysis show that, oxide layer on the surface of cracks can be divided into two layers. The main composition of outer-oxide layer is mainly the oxides of CoO, CoCr₂O₄ and a small amount of Cr₂O₃, evenly distributed on the crack surface with about 10 μm thickness. The inner-oxide layer discontinuous distribution with spherical and needlelike morphologies, mainly composed by oxides of Cr₂O₃ and Al₂O₃, the thickness is about 30 μm.

本研究主要研究涡轮导叶的失效机理以及失效叶片裂纹表面的氧化物成分。叶片材料为钴基高温合金DZ40M，具有定向凝固的晶粒结构。研究方法包括光学显微镜（OM）观察，扫描电子显微镜（SEM）观察和能量色散X射线光谱（EDS）分析。裂纹形貌观察结果表明：裂纹几乎分布在叶片中心的所有冷却孔排上，裂纹的宏观形貌是横向扩展的（垂直于定向凝固方向）。由于高温环境和维修期间循环热应力的作用，通过高能激光生产工艺产生的冷却孔附近的再结晶组织很容易成为裂纹的起点。由于高温下碳化物与基体之间的热膨胀系数相差较大，因此裂纹沿晶界和子界传播。氧化物成分分析结果表明，裂纹表面的氧化物层可分为两层。外部氧化物层的主要成分主要是CoO，CoCr的氧化物 裂纹表面上的氧化层可分为两层。外部氧化物层的主要成分主要是CoO，CoCr的氧化物 裂纹表面的氧化层可分为两层。外部氧化物层的主要成分主要是CoO，CoCr的氧化物₂ O ₄和少量Cr ₂ O ₃均匀地分布在裂纹表面上，厚度约为10μm。内氧化物层呈球形和针状形态的不连续分布，主要由Cr ₂ O ₃和Al ₂ O ₃的氧化物组成，厚度约为30μm。