High temperature oxidation of HFPD thermal-sprayed MCrAlY coatings

NiCrAlY and CoNiCrAlY powders were thermal-sprayed using the high frequency pulse detonation method (HFPD) onto AISI 310 austenitic stainless steel samples in order to obtain dense, adherent high temperature oxidation resistant coatings. The cyclic oxidation behaviour in air of both types of coatings was determined at a maximum temperature of 1273 K. The porosity, internal oxidation (after the first 8-h oxidation cycle), hardness, coating thickness and substrate-coating adherence were not significantly modified by the high temperature oxidation cycles. The surface phase composition was evaluated throughout the tests using X-ray diffraction and scanning electron microscope techniques revealing the formation of a continuous and highly protective alumina layer. The oxidation kinetics of both coatings can be characterized by parabolic rate constants, which are very similar to those of pure alumina.