The structure, oxidation resistance, mechanical and tribological properties of CrTiAlN coatings

Abstract

CrxTiyAlzN coatings (x+y+z=1) with low Al contents were deposited using hybrid high power impulse magnetron sputtering (HiPIMS) and pulsed dc magnetron sputtering (PDCMS). The Ti fraction (fTi=Ti/(Cr+Ti+Al)) was increased from 5 to 64% to produce coatings with different chemical compositions varied from Cr-rich to Ti-rich. The microstructure of the coatings was studied using X-ray diffraction and scanning electron microscopy. Mechanical properties of the coatings were analyzed by nanoindentation. The oxidation behavior of the coatings was evaluated in the ambient air at 900°C and 1000°C. The high temperature wear resistance of the coatings was measured using a high temperature pin-on-disc tribometer in the ambient air from 600°C to 900°C. The CrTiAlN coatings showed a (111) preferred orientation when the fTi is less than 10%. The orientation of the coatings changed from (111) to (311) as the fTi increased. The addition of a small amount of Ti (e.g., fTi=5–10%) effectively improved the mechanical properties and the wear resistance of the Cr0.66Al0.34N baseline coating. The Cr0.61Ti0.10Al0.29N coating exhibited the highest hardness of 40GPa, the lowest coefficient of friction of 0.4 and the lowest wear rate of 7×10−7mm3N−1m−1 at room temperature. The Cr0.61Ti0.10Al0.29N coating also showed excellent oxidation resistance after annealing at 1000°C and good wear resistance from 600°C to 800°C. These enhanced properties can be attributed to multiple factors including solid solution strengthening, the dense microstructure, and the strong (111) orientation. However, as the fTi increased from 20% to 64%, the oxidation resistance, mechanical properties, and wear resistance of the CrTiAlN coatings decreased.