Characterization of titanium chromium nitride nanocomposite protective coatings

Abstract

The structural, chemical, optical and mechanical properties of titanium chromium nitride nanocrystalline films deposited by ion beam-assisted deposition were studied by means of X-ray diffraction, X-ray photoelectron spectroscopy, spectroscopic ellipsometry, nanoindentation and wear testing. Coatings were deposited on silicon and stainless steel substrates with growth temperatures of 150 and 400°C. The concentration of titanium and chromium in the film was regulated by controlling their evaporation rates. The nitrogen concentration was controlled by varying the nitrogen ion current. X-ray diffraction and X-ray photoelectron spectroscopy measurements indicated that the films deposited at 150°C formed solid solutions whereas those produced at 400°C formed nanocomposites. The optical constants were measured using spectroscopic ellipsometry. A correlation between the elemental/phase composition and optical constants was established. The mechanical properties of the coatings were evaluated using nanohardness testing and were found to depend on composition. The nanocomposite films were the hardest (hardness of 30GPa and elastic modulus of 300GPa). Tribological properties of titanium chromium nitride coated 440C stainless steel coupons were evaluated using a ball-on-disk tribometer. These tests were conducted under a load of 50N for 1.5 million cycles at 180rpm. Coatings deposited at high temperature did not show any signs of wear.