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

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 degrees C. In situ high-energy X-ray diffraction showed that powdered face-centered cubic (fcc) CrTaN displays an excellent oxidation resistance up to similar to 1050 degrees C, where the formation of tetragonal (t) CrTaO4 and rhombohedral (r) Cr2O3 sets in. The compact CrTaN deposited on sapphire subjected to 1225 degrees 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. (c) 2021 The Author(s). Published by Elsevier Ltd on behalf of Acta Materialia Inc. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)

Automated summary

CrTaN coatings have gained increasing interest as suitable materials for metal cutting applications due to their combination of high hardness and increased fracture toughness. However, the mechanisms underlying the oxidation of this coating system are not thoroughly understood. This study revealed that CrTaN coatings exhibit excellent oxidation resistance up to approximately 1050 degrees C, where the formation of CrTaO4 and Cr2O3 compounds occurs. At 1225 degrees C, the structure evolution of the CrTaN coating includes 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.