LaB 6-based, Zr-alloyed, decorative hard coatings

Abstract

Dark-violet hard coatings based on LaB 6 are promising candidates for the extension of the conventional spectrum of decorative coatings. A promising approach which can overcome certain application-related problems, such as brittleness and insufficient adhesion, involves the alloying of these coatings with suitable elements or compounds. This paper presents some fundamental results on the structure and basic properties of LaB 6-based coatings alloyed with zirconium, employing simultaneous sputtering from two planar magnetrons supplied with LaB 6 and Zr targets. The characterization of the coatings was performed by scanning electron microscopy, electron probe microanalysis and X-ray diffraction. The results are discussed in terms of the hardness and optical properties of the coatings expressed by the CIE- L ∗a ∗b ∗ system. LaZrB films of varying composition were deposited using different magnetron current ratios for the two targets used. The film hardness decreases from approximately 2100 HV0.01 (LaB 6-based coatings) to 500 HV0.003 (Zr-based coatings), which corresponds to an increase in the Zr concentration in the films and a gradual shift of the morphology from LaB 6 through an amorphous phase to α- and ω-Zr. The brilliance values L ∗ are mainly determined by the Zr concentration due to the increasing metallic binding character within the coatings. The bluish colouration of the coatings decreases with increasing Zr concentration, whereas the reddish hue is almost unaffected. Finally, the alloying of decorative hard coatings seems to be a promising technique for the optimization of their properties.