Effect of coatings on microstructure and oxidation behavior of the Ni-based single crystal superalloys containing different Ru contents

The element Ru in single crystal superalloy usually plays an important role in inhibiting the mutual diffusion between coating and substate. The MCrAlY coating and PtAl coating were prepared on the fourth and third generation single crystal superalloy, and the isothermal oxidation behaviors of the two superalloys and the two coatings were investigated in static laboratary air at 1200 degrees C. The oxidation kinetic curves showed that the mass gain of the coated samples was less than the alloys without coatings, which meant the coatings showed more excellent oxidation resistance at high temperature, and the oxidation resistance of the two coatings was slightly enhanced by the addition of Ru during the oxidation tests. Meanwhile, the interdiffusion of elements, such as Al in coating and refractory elements in substrate, was hindered by the addition of ruthenium. The size of gamma' phase was also inhibited. As a result, the formation of interdiffusion zone and the precipitation of topological-close packed phase were suppressed, resulting that the DD91 showed more stable microstructure at elevated temperature than the DD90 during the oxidation process. The advantage of Ru in the alloys with coatings will be discussed in detail as well as the protective performance of coatings.