Laser cladding of CoNiCrAlY bond coat on Co-Ti-W alloy

Abstract

In this research, a CoNiCrAlY coating is deposited on $\gamma/\gamma'$-strengthened Co-Ti-W alloy upon laser cladding, and the microstructural evolution of the heat affected zone and the dilution effect on oxidation resistance were investigated. Using electron microscopy and atom probe tomography two distinct heat affect zones were observed, namely γ islands containing $\gamma'$ precipitate colonies and heat affected $\gamma/\gamma'$ regions outside the $\gamma$ islands comprising fine $\gamma'$ precipitates. Based on the experimental data and thermodynamic calculations, a model formation of these two heat affected zones was discussed. Oxidation behaviors of bare sample and CoNiCrAlY coated sample with two different dilution rates were investigated. Low Al concentration of highly diluted sample leads to absence of stable alumina layer after isothermal oxidation test. Lowly diluted sample formed alumina layer after oxidation which show that optimization of process parameter related to dilution rate are significant when depositing MCrAlY through laser cladding.