Annealing effects on nanostructure and mechanical properties of nanolaminated Ta–Zr coatings

This paper proposes Ta–Zr multilayer coatings fabricated by using magnetron co-sputtering, achieving high nanohardness and low roughness after annealing, as appropriate protective coatings for die materials. The as-deposited nanolaminated Ta–Zr coatings exhibited nanocrystalline or amorphous phases, depending on the chemical compositions. The Zr oxidized preferentially when annealed in oxygen-containing atmospheres. The nanohardness increased in relation to the oxygen content in the coating, which was attributed to the formation of a crystalline tetragonal ZrO2 phase. To serve as a protective coating when applied in high-temperature conditions with an appropriate nanohardness, such as coatings on glass molding dies, the coating must endure an annealing treatment in an oxygen-containing atmosphere at 600 °C. In this study, the periods of nanolaminated coatings were controlled by the rotation speed of the substrate-holder. The annealing treatments were conducted at 600 °C in atmospheres of 20-ppm and 50-ppm O2–N2. The variations in crystalline structure, nanohardness, and in-depth chemical composition profiles after various annealing durations were investigated. The feasibility of a protective Ta–Zr coating was improved by annealing the coating in a 1% O2–Ar environment for 30 min at 600 °C to achieve a nanohardness of 10 GPa, which is higher than the hardnesses of molded glasses, and by being subsequently exposed to a 10-ppm O2–N2 atmosphere, which is a realistic glass molding atmosphere.