Microstructure, oxidation behavior and adhesion of a CoNiCrAlTaY coating deposited on a high Nb–TiAl alloy by plasma surface metallizing technique

Abstract A CoNiCrAlTaY coating was deposited on the Ti–45Al-8.5Nb substrate by plasma surface metallizing technique. The microstructure, morphology and composition of CoNiCrAlTaY-coated specimens were studied by X-ray diffractometer, scanning electron microscope, and transmission electron microscopy. The as-prepared coating consisted of mixed phases including Al13Co4, CrCo, and Ni3Al, resulting in an increased microhardness. The Al2O3, CoO and Cr2O3 phases formed during initial oxidation at 900 °C. However, Al2O3 accompanied with CoCr2O4, NiCr2O4 and Cr2TiO5 phases generated during isothermal oxidation, which was responsible for the oxidation resistance. These oxides leaded to the increased surface hardness of the coated specimens. The adhesion strength between the CoNiCrAlTaY coating and Ti–45Al-8.5Nb substrate were improved caused by the interdiffusion of involved elements.