Abstract MCrAlY coatings deposited by LPPS or HVOF spraying are widely used on turbine blades and vanes to mitigate the effects of oxidation and corrosion. The service life of a MCrAlY layer is dependent on the loss of aluminum, which is consumed by oxidation on the surface and by diffusion into the substrate. After long term heat treatments in air, LPPS and HVOF CoNiCrAlY coatings on IN738 and Hastelloy X substrates were examined and their interdiffusion and Al depletion layers were characterized based on the distribution of phase constituents, the amount of residual Al content, and average layer thickness. The results of the study show that differences in coating behavior with respect to Al consumption are mainly due to the oxidation of yttrium in the CoNiCrAlY powder during HVOF spraying.