Heat treatment of decorative TiN coatings as a color control method

Abstract

The paper presents the results of a study of decorative properties of gold-colored titanium nitride (TiN) ion-plasma coatings deposited on austenitic stainless steel substrates. The known method of obtaining a wide range of colors is the heat treatment of TiN films at temperatures above 500°C. The aim of the present paper is to extend the hue range of TiNi coatings by means of annealing in oxidizing environment at temperatures up to 500°C. Uniform chromaticity CIEL*a*b* system was chosen as the colorimetric system due to its convenience in color identification, determination of color-difference coordinates and the degree of approximation to a reference material. Chromaticity of decorative TiN coatings was determined by three components, a* and b* representing the color hue and L* indicating its intensity. Regularities of changes in the color characteristics of TiN coatings after low-temperature annealing have been determined and the possibility of controlling the color hue and intensity of TiNi coatings by varying heat treatment parameters has been demonstrated. It has been shown that in the temperature range 300 to 500°C it is possible to achieve an enhancement or weakening of particular components (red or yellow) of the resulting color that manifests itself in a variation of the TiNi coating tone color in the limits of yellow-red spectrum region. Starting at T = 400°С, a decrease of the intensity (lightness value) with annealing time has been revealed. Optimization of the regime of heat treatment of TiNi coating has allowed maintaining the lightness on the level of the initial coating and achieving the best approximation of the coating color to the one of gold alloy ZlSrM 900-40, which was chosen as a reference material and is used in fabrication of dental prostheses.