Modeling of microstructural evolution and lifetime prediction of MCrAlY coatings on nickel based superalloys during high temperature oxidation

MCrAlY coatings are deposited onto superalloys to provide oxidation and corrosion protection at high temperature by the formation of a thermally grown oxide scale. In this project, the oxidation behavior of a HVOF CoNiCrAlYSi coating on IN792 was studied for both isothermal oxidation (900, 1000 and 1100 °C) and thermal cycling (100-1100 °C). The microstructural evolution of the CoNiCrAlYSi coatings after oxidation was investigated. It was found that the Al-rich β phase is gradually consumed due to two effects: surface oxidation and coating-substrate interdiffusion. Some voids and oxides along the coating-substrate interface, or inside the coating, were considered to play a role in blocking the diffusion of alloying elements. Based on the microstructural observation, an oxidation-diffusion model, considering both surface oxidation and coating-substrate interdiffusion, was developed by using Matlab and DICTRA software to predict the useful life of MCrAlY coatings. A new concept of diffusion blocking is also introduced into the model to give more accurate description on the microstructural evolution. The results from modeling and the experimentally established composition profiles showed good agreement.