An Analytical Approach From Oxide Growth Kinetics to the β-Phase Depletion Behaviour in a CoNiCrAlY Coating

This paper presents an analytical solution to predict the β-phase depletion behaviour from the oxide growth kinetics in a CoNiCrAlY coating. The CoNiCrAlY coating was prepared by low pressure plasma spraying (LPPS) and was characterised by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). It exhibited a two-phase structure, consisting of a fcc γ-Ni phase and a bcc β-NiAl secondary phase. The as-sprayed CoNiCrAlY coatings were subjected to isothermal oxidation at 1100 °C. An analytical approach was proposed to estimate the β-phase depletion behaviour from the oxide growth kinetics via mass balance conversions. In addition, the growth of mixed oxides (including spinel oxides and alumina) on the rough and flat surfaces in the as-sprayed condition were considered. It was shown that the calculated β-phase depletion agreed well with the experimental measurements. The work reported in this study presents a rapid evaluation on the β-phase depletion behaviour in MCrAlY coatings.