Tuning Colors in Protective Metal nitride Coatings by the Control of Absorption/Interference Effects

摘要

Nitride coatings are widely used in decorative applications due to their attractive colors and good mechanical properties. In the case of thick (>1 micron) and optically absorbing coatings, only intrinsic color of the nitrides are exploited, which is solely determined by the stoichiometry of the coating and can be varied only in a limited range. However, if the coating is thin enough and partially transparent, an additional degree of color control is possible by including interference effect in the design. The color can then be further tuned by adding other layers, such as a reflective coating between the top layer and the substrate. In this work, this principle is demonstrated for the case of tribological TiAlN coating. Coatings with two different compositions (50:50 and 30:70 of Ti: Al) were prepared by sputtering onto stainless steel, Si and TiN-pre-coated substrates. By varying the thickness of coating in the range between 20 and 100 nm, saturated colors were obtained, including yellow, violet and blue. Only a small variation in color was observed with changing angle of view. Optical properties of the coatings were characterized by spectrophotometry and ellipsometry, and quantified colors were represented in the Lab color space for different film compositions, thicknesses and substrate reflectivity.