Experimental investigation on high-temperature fatigue failure of different bolts of Ni-based superalloy GH4169 in an aero-engine

Recently, a coupling bolt fractured in the low cycle fatigue test of an aero-engine gas turbine in China. To investigate the reason for bolt failure, three types of bolts used in the gas turbine and standard specimens manufactured by Ni-based superalloy GH4169 were axially fatigued at 600°C and 650°C. Scanning electron microscope (SEM) was applied to observe and analysis the fracture surfaces of failure specimens. Results showed that the fatigue life of specimen increased with increasing the material hardness. The bolt tested at 600°C had a higher fatigue life than the same bolt tested at 650°C. The element segregation differences among different bolts might have a significant effect on the discrepancies among fatigue lives. Thus, it was suggested that hardness testing should be operated on the as-received GH4169 alloy bars, and the bolts should be manufactured by the higher hardness bars. The temperature of the bolt in service should be monitored, and appropriate actions should be taken to lower the bolt temperature.