Structural and mechanical responses of (Zr,Al)N/ZrB2 superlattice coatings to elevated-temperature annealing

Multilayered (Zr,Al)N/ZrB2 coatings with bilayer periods of 2–10 nm were deposited by reactive magnetron sputtering. The coatings were subsequently annealed at elevated temperatures of 850–1000 °C for 1 h, followed by characterization using low-angle X-ray reflection, high-angle X-ray diffraction, and nanoindention. A marked polycrystalline multilayered structure with bilayer periods of 3–6 nm and a thickness of 1.5 μm corresponds to the highest hardness. The hardness values increased from 28 GPa to nearly 40 GPa and compressive residual stress was about 0.4 GPa after annealing. These properties were related to strong mixed ZrN preferred orientations as well as to crystalline ZrB2 with (0 0 1) texture. The formation of AlO and ZrO bonding after annealing also helped to improve thermal stability of the structure.