Influence of coating thickness and substrate elasticity on the tribological performance of PEEK coatings

Poly-ether–ether–ketone (PEEK) coatings are often applied as solid lubricant films in tribosystems because of their notable wear resistance, corrosion resistance, and self-lubricating capacity. However, little is known about the effect of coating thickness on the plastic deformation, residual stresses and energy dissipation of PEEK when placed under sliding load. Moreover, the effect of substrate rigidity on coating stresses and deformation under sliding load are also under-researched. Having such knowledge is of significant importance in order to reduce damage of engineering parts and extend their lifetime. In this study, the effects of PEEK coating thickness and substrate elasticity are analyzed using a 3D ball-on-flat finite element model as well as experimental analysis using a linear reciprocating tribometer. The experimental tests were performed with samples that incorporated PEEK coatings of various thicknesses on alumina and steel substrates. It was found that under a constant normal load, stresses, strain and energy dissipation were sensitive to both substrate material and coating thickness. Thicker coatings were shown to provide a cushioning effect to the substrate under high stress. Additionally, PEEK-coated alumina samples demonstrated a lower friction coefficient than steel samples with coatings of similar thickness. It was shown from both simulation and experiment, the optimum combination, within the range the experiments were conducted, for minimizing residual stress and possible fatigue damage was an alumina substrate with a relatively thick PEEK coating layer.