Abstract: By means of stereomicroscopy and scanning electronic microscopy(SEM),the fracture mode and mechanism of the broken K18 superalloy cast blade in a supercharger turbo were investigated.A blade with a heavy fracture appearance has been confirmed to be the source of the accident,and some other blades displaye damage with various degrees.The fracture mechanism of this blade is due to fatigue fracture under conditions of high rotational speed and high temperature,and the crack source of this blade is a casting defect of cold shut located beneath the subsurface of this blade for 1 cm.