Some considerations on the mitigation of fretting damage by the application of surface-modification technologies

Fretting is a surface-degradation process due to mechanical and chemical at tack by small-amplitude oscillatory movement between two contacting surface s and it is intimately related to wear, corrosion and fatigue. The introduc tion of surface treatments or coatings is expected to be an effective strat egy against fretting damage. This paper discusses the application of severa l types of advanced surface-modification methods for the mitigation of fret ting damage, such as physical and chemical vapour deposition (PVD and CVD), ion implantation, laser treatment and plasma nitriding, etc. Some coatings are effective in the mitigation of the fretting wear, whereas others are m ore effective under fretting fatigue conditions. The effects of surface-mod ification methods on fretting resistance are explained using fretting maps. There are at least five different mechanisms in using surface-modification methods to increase fretting resistance: (1) inducing a residual compressi ve stress; (2) decreasing the coefficient of friction; (3) increasing the s urface hardness; (4) altering the surface chemistry; (5) increasing the sur face roughness. Apart from this, the intrinsic properties of the coatings, such as their density and mechanical and chemical properties as well as the adhesion condition with the substrate, also significantly affect the perfo rmance of the coatings under fretting conditions. Based on this rationale, a coating-selection method was proposed to select the most appropriate surf ace treatments or coatings to minimise the probability of fretting damage. Selection of a process is guided primarily by identification of the frettin g failure modes, and the ability to adjust and obtain the required surface properties, with a balance between the precise control of the surface prope rties and the process cost. (C) 2000 Elsevier Science S.A. All rights reser ved.