Oxidation resistance and mechanical properties of Cr–Ta–Si–N coatings in glass molding processes

In this study, Cr–Ta–Si–N coatings were prepared using reactive magnetron co-sputtering on silicon wafers and cemented carbide substrates to evaluate their feasibility for protective purposes on glass molding dies. The nitrogen gas flow-rate ratio (N2/(N2 + Ar)) was set at 0.4 to fabricate the Cr–Ta–Si–N coatings with an overstoichiometric ratio, N/(Cr + Ta + Si) > 1, for the rock salt structure. The as-deposited Cr–Ta–Si–N coatings, with Cr and Si contents in the ranges of 1–15 at.% and 9–15 at.%, respectively, exhibited a nanohardness of 14.6–21.6 GPa and a surface roughness of 0.4–1.0 nm. The coatings with a Si content between 11 and 15 at.% exhibited X-ray amorphous. Annealing treatments were conducted in a 1% O2–99% Ar atmosphere at 600 °C for 500 min, which is an oxidation-accelerating condition, and thermal cycling annealing was conducted at 270 °C and 600 °C in a 15 ppm O2–N2 atmosphere, which is a realistic glass molding atmosphere for mass production. The outward diffusion of Si resulted in the formation of a Si-oxide scale 12–14 nm thick, thus maintaining a surface roughness of approximately 1 nm and confirming the thermal stability of the Cr–Ta–Si–N coatings. The chemical inertness of the Cr6Ta25Si11N58 coating during the molding of B2O3–ZnO–La2O3-based and SiO2–B2O3–BaO-based glasses was evaluated.