Annealing of sputter-deposited nanocrystalline Cr–Ta coatings in a low-oxygen-containing atmosphere

As a protective hard coating on glass molding dies, Cr–Ta coatings were fabricated on binderless tungsten carbide substrates with a Ti interlayer by RF magnetron sputtering. The nanocrystalline Cr–Ta coatings were deposited at 550 °C, which revealed one nanocrystalline phase for the Ta-rich coating and two nanocrystalline phases for the Cr-rich coating. Annealing treatment was conducted at 600 °C in a 12 ppm O2–N2 atmosphere to evaluate the coating performance in a realistic glass molding environment. Both Auger electron spectroscopy and X-ray photoelectron spectroscopy depth profiles verified the outward diffusion of Cr, which formed a protective coating for the Cr-rich coatings. A scale of Cr2O3 and a Cr-depleted transition zone near the surface were identified by conducting a transmission electron microscopy investigation on the annealed Cr0.71Ta0.29 coating. The Cr-rich coating absorbed a smaller amount of oxygen, exhibited greater hardness, and maintained nanoscale surface roughness after annealing in the glass molding atmosphere, thus making it an appropriate protective coating for the die material.

► We prepared amorphous or nanocrystalline Cr–Ta coatings using RF magnetron sputtering.
► The outward diffusion of Cr formed a protective coating for the Cr‐rich coatings.
► The surface roughness of the annealed Cr-rich coatings was remained at a nanoscale.
► The Cr-rich coatings became an appropriate protective coating for the die material.