Diffusion of Ta and its influence on oxidation behavior of nanocrystalline coatings with different Ta, Y and Al contents

Oxidation behavior of a Ta-containing nanocrystalline coating with different contents of Y and Al on the N5 single-crystal superalloy is investigated at 1050 and 1150 °C. Results indicate that the refractory element, Ta, is very active during oxidation. It diffuses easily from the interior of the nanocrystalline coating to the interface of coating/scale in the form of γ′-Ni3(Al, Ta), where it is oxidized and ruins the compactness of oxide scale. Adding moderate amount of Y retards the movement and oxidation of Ta, thus increases oxidation resistance. Such retarding effect is strengthened by increasing Al content, while weakened by increasing temperature.