Effect of N2 to total pressure ratio on the structure, mechanical and tribological properties of magnetron-sputtered Ti-Al-Ta-Si-N coatings

Abstract

Ti-Al-Ta-Si-N coatings produced by reactive DC magnetron sputtering at the nitrogen to total pressure ratio (pN2/pt) varying from 0.1 to 0.4 are studied. Using energy dispersive X-ray spectroscopy it is shown that pN2/pt has a pronounced effect on the elemental composition of the coatings. Ti and Al contents vary most significantly that causes the Al/Ti ratio to change from 0.68 to 1.20 within a pN2/pt range of 0.1 to 0.17, which is followed by its decrease down to 0.85 at pN2/pt = 0.4. X-ray diffraction measurements reveal that (200) texture of the face-centered cubic structure evolves with increasing the pN2/pt ratio. It is found that while the coating obtained at pN2/pt = 0.1 has featureless fracture cross-section morphology, the sample deposited at pN2/pt = 0.17 exhibits pronounced columnar morphology. In contrast the coatings produced at pN2/pt ≥ 0.23 are characterized by denser microstructure with no obvious columnar grains. The evolution of the structure and chemical composition results in variations of the hardness, the reduced Young's modulus, adhesion and wear resistance of the Ti-Al-Ta-Si-N coatings. The coating deposited at pN2/pt = 0.23 is found to be characterized by an optimal combination of the reasonably high mechanical characteristics along with improved adhesion and wear resistance. Due to the dense fine-grained microstructure, its wear rate is almost four times lower than that of the coating obtained at pN2/pt = 0.1.