目的 探究某重型燃气轮机涡轮叶片服役过程中表面裂纹的形成原因。方法 利用场发射扫描电子显微镜及能谱仪确定开裂叶片裂纹周围的显微组织及元素分布情况，揭示高温氧化导致的涂层外表面及涂层/叶片基体界面处的组织演变规律。结果 此叶片经高温长时间服役后，表面未发现热障涂层，抗氧化涂层是NiCoCrAlY涂层，主要显微组织为γ-Ni相+β-NiAl相;叶片基体材质为GTD-111镍基高温合金，主要显微组织为γ-Ni相+γ?-Ni3(Al, Ti)相及γ/γ?共晶组织和块状(Ti, Ta)C碳化物。表面裂纹主要集中于叶身与叶根的过渡平台位置。涂层内部、裂纹周围及涂层/叶片基体界面处均发现明显的金属氧化现象，氧化产物主要为金属Al和Cr的氧化物。高温服役环境下，铝元素的氧化导致涂层外表面的β-NiAl相及涂层/叶片基体界面位置的γ?-Ni3(Al, Ti)相向γ-Ni相转变，导致上述2位置的弱化。此外，截面形貌表明，在涂层表面位置，裂纹与凹坑相连接，并呈现向涂层内部扩展的态势，局部位置已贯穿抗氧化涂层，并扩展进入叶片基体。结论 由于高温氧化导致涂层表面Al含量的显著下降，富Al的β-NiAl强化相转变为γ-Ni相，在表面已存在凹坑的前提下，加之较大的应力集中于叶身与叶根过渡区域，导致涂层表面的开裂及向内的裂纹扩展。

The work aims to investigate the reasons for surface cracking of a first stage rotor blade in a heavy duty gas turbine, which has been in service for about 80 000 h. The microstructures and corresponding element distribution at the critical positions of the cracked blade were determined with field emission scanning electron microscope (FESEM) and energy disperse spectroscopy (EDS). The microstructure evolution both at the surface position of the coating and at the interface between the coating and the substrate of blade caused by the high-temperature oxidation in the service process were revealed. A coating with single-layer structure and corrugated surface morphology was observed on the surface of the blade. The results of EDS analysis confirmed that this coating with high contents of elements Co, Ni, Cr and Al was the anti-oxidation coating (or named as bonding coating) rather than thermal barrier coating. Besides, the protective thermally grown oxide layer which was usually formed during high-temperature service was not observed on the top surface of anti-oxidation coating for the blade. It could be inferred that the thermal barrier coating as well as the thermally grown oxide layer on the top surface of the blade fell off in the service process. The anti-oxidation coating was NiCoCrAlY alloy with a mixture microstructure of γ-Ni+β-NiAl phases, while the blade substrate was GTD-111 nickel-base superalloy with a mixture microstructure of γ-Ni+γ?-Ni3(Al, Ti) matrix, γ/γ? eutectic and (Ti, Ta)C carbides. The surface cracks were mainly distributed at the transition platform between the airfoil and the root section of the blade. In addition, the cross sectional morphology indicated that the surface cracks originated from the thermal erosion pits which formed on the surface of the coating in the long-term service process, and then gradually grew into the interior in the following high temperature service process. Severe metal oxidation in the inner of cracks demonstrated that the cracks facilitated the inward diffusion of oxygen and accelerated the oxidation of metal elements. The accumulation of elements sulfur and vanadium which mainly came from the corrosive contaminants contained in the air and fuel was detected in the inner of the cracks. Furthermore, plenty of oxides were also found in the inner of the anti-oxidation coating and at the interface between the coating and blade matrix. The oxidation products were mainly composed of oxides containing elements Al and Cr. The oxidation of element aluminum during service induced the phase transformation from β-NiAl to γ-Ni at the surface position of the coating and γ?-Ni3(Al, Ti) to γ-Ni at the interface between the coating and the substrate of blade. The β-NiAl phase acted as a strengthening phase played a significant role in determining the performance of the coating. The formation of γ-Ni layer accompanying with the disappearance of β-NiAl phase on the top surface of the coating lead to the deterioration of mechanical properties. It can be concluded that the disappearance of the high hardness β-NiAl phase combining with the surface hot-corrosion pits and stress concentration result in the formation and propagation of cracks at the transition platform between the airfoil and the root section of the blade.