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 degrees 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.