Thermal stability of laminated Ru–Al/Ru–Al–Zr coatings on Inconel 617

Abstract

Ru–Al–Zr multilayer coatings with a Ru interlayer were fabricated through cyclical gradient concentration deposition by using direct current magnetron cosputtering on Inconel 617 substrates. The thermal stability of these Ru–Al–Zr coatings after annealing at 800 °C in ambient air was investigated through X-ray diffraction, Auger electron spectroscopy, and transmission electron microscopy. A multilayered structure of the Ru–Al–Zr coatings was maintained, transformed to small grains, and grew into large grains as the annealing duration was increased from 30 min to 4 h, and then to 12 h, which was accompanied with the outward diffusion of Ni, Cr, and Co from Inconel 617 substrates. Moreover, the Ru–Al–Zr coatings could not prevent the inward diffusion of oxygen. With the deposition of a Ru–Al top coating, the laminated Ru–Al/Ru–Al–Zr coatings restricted the inward diffusion of oxygen by forming a continuous Al2O3 scale.