DECORATIVE HARD COATINGS - ADVANCES IN OPTICAL CHARACTERIZATION TECHNIQUES

Transition metal compounds are finding increasing use in decorative co atings, combining intense colour, high wear resistance and good corros ion resistance. From the decorative point of view, colour and gloss ar e the most important features. The physiological colour impression is well described by the CIE-La*b colour space. Integrating sphere measu rement (ISM) and goniospectroscopy (GS) derive colours from a measurem ent of the spectral reflectance factor R(lambda) relative to a white r eference. Spectroscopic ellipsometry (SE) is a reference-free techniqu e for measuring amplitude ratios and phase changes of polarized light upon specular reflectance. ISMs of (Zr,Y)N coatings are presented, whi ch show considerable yellow and red values at intermediate lightnesses . The effect of the surface roughness is discussed for TiN coatings. T he angular dependence of La*b* and the behaviour of R(lambda) are sho wn by means of GS for these TiN coatings in off-specular directions. T hese results of ISM and GS are compared with the SE data. The high sen sitivity of SE to changes in stoichiometry as well as the capability o f separating additional interference effects are demonstrated for (Zr, Cr)N and (Zr,Al)N coatings. However, it is shown especially in the cas e of rough surfaces that each technique is helpful in distinguishing f eatures of physical and physiological interest.