Specially designed SEM in situ fatigue tests have been conducted to trace the whole process of crack initiation and propagation to fracture in an Al2O3 seeded P/M Rene 95 superalloy.The results show that the loading wave shape has a strong effect on the micromechanical behavior.Under triangle wave loading crack initiation and propagation life decrease on the inclusion/matrix interface,but specimen failure is not due to the surface or sub surface inclusions.On the other hand,sine wave loading is accompanied by a significant increase the crack initiation life and surface or sub surface inclusions are always the primary cause of fatigue fracture.Furthermore,under the same loading waveform the crack initiation life increases as the amplitude of applied stress decreases.