Damage Mechanisms under Fretting of Self-mated Stainless Steel (SS 316L) and Chromium Carbide Coatings

Fretting is of a serious concern in many industrial components, specifically, in nuclear industry for the safe and reliable operation of various component/system. Comprehensive experimental and numerical studies have been carried out to understand the mechanics and mechanisms involved under fretting conditions. Experiments were performed on a first-of-a-kind fretting machine, with the capabilities of simulating different fretting regimes under ambient and high vacuum (10–5mbar) conditions and, temperatures up to 873K. Studies were made on self-mated stainless steel (SS) and stainless steel mated against coated surfaces. Chromium carbide with 25% nickel chrome binder coatings using plasma spray and High Velocity Oxy Fuel (HVOF) processes on SS were investigated in detail. As evident from the experimental studies, the initiation or nucleation of damage in self-mated SS is due to severe plastic deformation. Ratcheting has been observed as the governing damage mode under cyclic tangential loading condition. Once the crack has been initiated under ratcheting, the propagation is controlled by fatigue. The orientation of crack propagation has been observed to be governed by the contact conditions prevailing at the contact interface. Numerical analysis result shows that the propagation of the subsurface cracks is controlled by strain energy release rate.