Experimental and Theoretical Study of Coating Spalling under High-Cycle Fractional Loading

Abstract

An experimental and theoretical study of contact fatigue damage accumulation at the coating-substrate interface has been carried out for the case of frictional contact between a smooth coating and a rough counterbody. Coatings were synthesized via low-temperature thermal decomposition of metal (Al, Zr) carboxylate solutions, which resulted in the formation of nanoscale amorphous nanocrystalline oxide layers 20–400 nm thick (depending on the concentration of the film-forming solution and the number of loading cycles) on the substrate surface (quartz glass). The investigation included coating deposition, determination of coating mechanical properties by indentation, development of the friction test procedure, stress calculation at the coating-substrate interface by modeling high-cyclic frictional loading, and the choice of a damage accumulation model for the coating-substrate interface that relates the stress state to the number of cycles to coating spalling. Preliminary tests revealed the coating compositions and coating deposition techniques that provide the highest spalling resistance under cyclic contact loading. Parameters in the relation for contact fatigue damage accumulation were determined and the model was verified by analyzing the experimental load dependence of the number of cycles to coating spalling on the microscale. It has been shown that the linear damage summation model conventionally used for describing failure due to fatigue damage accumulation in some materials can be applied to investigate the coating-substrate interface whose properties depend not only on the properties of the interfacing materials but also on the coating deposition technique.