Oxidation resistance and mechanical properties of Zr–Si–N coatings with cyclic gradient concentration

Abstract

Zr–Si–N coatings with cyclic gradient concentration were fabricated using reactive direct current magnetron cosputtering. The low-Si-content coatings, Zr60N40 and Zr58Si2N40, exhibited a face-centered cubic (f.c.c.) structure, accompanied with a nanohardness of 21.0–23.6GPa and a Young's modulus of 248–267GPa, whereas the medium-Si-content coatings, Zr54Si6N40 and Zr52Si8N40, exhibited a mixture of f.c.c. and near-amorphous structures, accompanied with a nanohardness of 19.7–18.4GPa and a Young's modulus of 204–207GPa. When the Si content ranged from 14 to 19at.%, the structures of Zr–Si–N coatings were X-ray amorphous; those coatings exhibited lower nanohardness levels of 13.7–10.3GPa and Young's modulus values of 196–148GPa. The high-Si-content coatings, Zr28Si24N48 and Zr22Si30N48, exhibited an amorphous structure, accompanied with a nanohardness of 13.7–16.2GPa and a Young's modulus of 196–217GPa, which were higher than those of the coatings with a Si content of 14–19at.%. Coatings formed by adding Si into the Zr–N matrix and performing annealing at 600°C in a 1% O2–99% Ar atmosphere showed notably high oxidation resistance because Si–Zr–O oxide scales formed on the surfaces. The mechanical properties of crystalline Zr–Si–N coatings declined after annealing, whereas near-amorphous Zr–Si–N coatings retained high levels of mechanical properties after annealing.