Modelling of phase equilibria in MCrAlY coating systems

Selection of high temperature coatings and structural materials, used in turbine applications, requires extensive understanding of materials phase equilibria at elevated temperatures for the estimation of long-term materials behaviour. With the advent of computer modelling means, involving reliable thermodynamic and kinetic databases, it is now possible to predict phase changes and interdiffusion processes in such systems. The present paper discusses the application of one such computer modelling in understanding the effects of cobalt and rhenium additions on the phase stability in Ni–Cr–Al coating systems. The results of modelled phase formations and phase changes as a function of temperature are extensively discussed in the light of detailed experimental verifications involving light and electron microscopy and X-ray diffraction studies. The presented results illustrate that the applied computer modelling does predict the phase formations to a high degree of reliability with all the elements investigated. Phase movements predicted on exposures to high temperatures up to 1050 °C match closely with the experimental determinations. Minor differences have been observed between the modelling and the experimental results for the alloys containing high amounts (≥20 wt.%) of cobalt.