Annealing and oxidation study of Ta–Ru hard coatings

Refractory metal alloy coatings have been widely used as protective coatings on glass molding dies. The formation of intermetallic compounds in the coatings inhibits grain growth at high-temperature environment in the mass production of optical components. The current work presents Ta–Ru coatings with a Cr interlayer on cemented carbide substrates and silicon wafers deposited by direct current magnetron co-sputtering at 400 °C. The as-deposited Ta–Ru coatings possessed a hardness of 13–14 GPa and a surface roughness of 1.3–4.0 nm. The annealing treatments were carried out at 600 °C under two vacuum levels of 3 × 10− 3 and 3 Pa, respectively. After annealing in vacuum at 3 × 10− 3 Pa, the Ta–Ru coatings showed grain size, hardness, surface roughness and phase stability comparable to those of the as-deposited coatings. While annealing in vacuum at 3 Pa, preferential oxidation of Ta in the Ta–Ru coatings was verified by X-ray photoelectron spectroscopy, a variation of the chemical composition in depth was analyzed by Auger electron spectroscopy and the internal oxidation zone consisting of a laminated structure was observed by transmission electron microscopy.