Preparation and annealing study of CrTaN coatings on WC-Co

► We prepared crystalline CrTaN coatings by reactive d.c. magnetron sputtering. ► Oxygen diffused into the CrTaN coatings after annealing in air in excess of 500 °C. ► CrTaN coatings served as diffusion barriers for outward diffusion of Co up to 600 °C. ► A 50 ppm O2-N2 atmosphere was used as the glass molding atmosphere. ► CrTaN coatings are appropriate protective coatings under a glass molding atmosphere.