Microstructure Features of Cold-Sprayed NiCoCrAlTaY Coating and its High Temperature Oxidation Behavior

Superalloy coating was deposited by cold-spraying using a commercial NiCoCrAlTaY powder. The coating microstructure was investigated by scanning electron microscopy and X-ray diffraction to reveal the change of the b-NiAl phase in the as-received powder particle during coating deposition. The oxidation behavior of the cold-sprayed MCrAlY coating and its microstructural evolution during the isothermal treatment were examined. The results show that significant microstructural change occurred to NiCoCrAlTaY superalloy during cold spraying and the thermal exposure. The intensive plastic deformation upon high velocity impact of spray particles results in transformation of b-NiAl to the matrix phase, forming metaltable b-NiAl depletion zones (b-PDZs) which are distributed around the boundaries of deposited particles in the coating. The central part of the deposited particles with limited deformation retained the original phase constitutions of the starting powder. The b-phase with fine grains is re-precipitated uniformly in the areas in b-PDZs in the as-sprayed coating during high temperature exposure. A stable Al2O3 scale was formed on cold-sprayed NiCoCrAlTaY during oxidation possibly due to active b-PDZs on the top surface of the coating.