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

- Zr-Si-N coatings with cyclic gradient concentration were prepared using cosputtering.
- The nanohardnesses increased 1-3 GPa, relative to those of the monolithic Zr-Si-N.
- As-deposited high-Si-content (> 14 at.% Si) Zr-Si-N coatings were near-amorphous.
- Si-Zr-O scales that formed on high-Si-content coatings improved oxidation resistance.
- Annealed high-Si-content (> 15 at.% Si) coatings retained mechanical properties.

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 21.0-23.6 GPa and a Young's modulus of 248-267 GPa, 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 19.7-18.4 GPa and a Young's modulus of 204-207 GPa. When the Si content ranged from 14 to 19 at.%, the structures of Zr-Si-N coatings were X-ray amorphous; those coatings exhibited lower nanohardness levels of 13.7-10.3 GPa and Young's modulus values of 196-148 GPa. The high-Si-content coatings, Zr28Si24N48 and Zr22Si30N48, exhibited an amorphous structure, accompanied with a nanohardness of 13.7-16.2 GPa and a Young's modulus of 196-217 GPa, which were higher than those of the coatings with a Si content of 14-19 at.%. 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.