Oxidation resistance of cathodic arc evaporated Cr0.74Ta0.26N coatings

Abstract

Owing to their combination of high hardness and increased fracture toughness, CrTaN coatings have recently gained increasing interest as suitable candidates for metal cutting applications. However, up to now, the detailed mechanisms underlying the oxidation of this promising coating system are not thoroughly understood. Thus within this work, the evolution of microstructure and phase composition of a cathodic arc evaporated Cr0.74Ta0.26N coating were illuminated in ambient atmosphere up to 1400 °C. In situ high-energy X-ray diffraction showed that powdered face-centered cubic (fcc) CrTaN displays an excellent oxidation resistance up to ∼1050 °C, where the formation of tetragonal (t) CrTaO4 and rhombohedral (r) Cr2O3 sets in. The compact CrTaN deposited on sapphire subjected to 1225 °C in ambient atmosphere exhibits intact fcc-CrTaN regions near the substrate, a porous intermediate layer of r-Cr2O3 and t-CrTaO4 and a dense r-Cr2O3 oxide scale at the surface.