Review of fatigue of coatings/substrates

A review of fatigue of coatings/substrates is presented. Fatigue damage is either local or general, depending on the range of cyclic loads. Local fatigue damage includes rolling contact fatigue (RCF), fretting fatigue, fatigue-wear and general wear. Applied loads are localized consisting of rolling contacts or sliding contacts, and the resulting damage is mostly surface related. Crack initiation, surface pitting, delamination, spalling, buckling and enhanced wear can result from local fatigue damage of coatings. General fatigue damage results when the loads are of longer range such as cyclic bending, torsion or uniaxial or biaxial tension/compression etc. The mechanics of fatigue, role of microstructure, micromechanics in terms of crack nucleation, growth and fracture are reviewed. Defects produced during processing form precursors for crack nucleation. It is shown that optimization of the processing conditions to minimize defect density is essential. to enhance fatigue resistance of coatings/substrates.