Laminated structure in internally oxidized Ru–Ta coatings

Abstract

During the development of refractory alloy coatings for protective purposes at high temperature under oxygen-containing atmospheres, previous studies noted and examined the internal oxidation phenomenon for Mo–Ru and Ru–Ta coatings. The internally oxidized zone shows a laminated structure, consisting of alternating oxygen-rich and deficient layers stacked with a general orientation. Previous studies proposed a forming mechanism. To investigate in detail, Ru–Ta coatings were prepared with various rotating speeds of a substrate-holder. The coatings were annealed at 600°C in an atmosphere continuously purged with 1% O2–99% Ar mixed gas for 30min. Transmission electron microscopy was used to examine the laminated-layer periods. Auger electron spectroscopy depth profiles certified the periodical variation of the related constituents. X-ray photoelectron spectroscopy proved the valence variation of Ta in the near surface, accompanied by the introduction of oxygen ions. The inward diffusion of oxygen was dominated by lattice diffusion.