Fretting fatigue damage accumulation in PH13–8Mo stainless steel

The accumulation of fretting fatigue damage in PH13–8Mo stainless steel was investigated by interrupting experiments at several proportions of the total fretting fatigue life. The interruption intervals were chosen to correspond to changes in the frictional force range evolution behavior. Fretting scars and orthogonal sections through them were examined to determine the extent of surface damage and subsurface deformation and cracking. Cracks developed due to fretting within the first 200 cycles (0.14% of total life), and significant subsurface deformation was observed after only 3.5% of the total fretting fatigue life. A microstructurally altered region, which showed a marked increase in hardness, extended to a depth of approximately 80 μm below the scar. The final catastrophic crack nucleated near the interface between the harder and softer regions. Nanoindentation and scanning electron microscopy were used to determine the connection between the observed microstructural changes and the regions of varying hardness.