Failure Analysis of GH4033 Nickel Based Alloy Coupling Ring of an Aircraft Engine

During the overhaul decomposition inspection of an aircraft engine, it was found that serious deformation and cracking occurred in the coupling ring of stage Ⅱ turbine guide. The cause of the deformation and cracking was analyzed by macro- and micro-morphology observation, fracture analysis, chemical composition analysis and hardness test. The results show that the cracks in the inner wall of the installation hole of the coupling ring were high cycle fatigue cracks. The fit clearance between axle neck of the guide vane and installation hole of the coupling ring, and the gap between lower edge plates of the guide vane were both small; the linear expansion coefficients of the guide vane and the coupling ring were different and therefore the axle neck could not move freely in the installation hole under high temperature condition. Under the thermal stress, the coupling ring was extruded to the center, resulting in the deformation and fatigue cracking. The periodic change of the clearances caused by temperature variation was the main reason for fatigue crack growth. The similar accidents could be effectively avoided by properly reducing the size of the axial neck of stage Ⅱ turbine guide vane to enlarge fit clearance between the axle neck and the binding ring installation hole as well as the gap between lower edge plates of the guide vane.