OPTICAL-PROPERTIES AND CORROSION BEHAVIOR OF SPUTTERED ZR-B AND ZR-B-N COATINGS

In this paper, we present results on the structure, optical properties and corrosion behaviour of Zr-B and Zr-B-N coatings employing non-rea ctive and reactive d.c. magnetron sputter deposition. The addition of nitrogen reduced the grain size-coatings deposited at nitrogen flow ra tes f(Ng) of less than approximately 14 sccm (standard cm3 min-1) were extremely fine grained, while nitrogen flow rates of more than 14 scc m led to fracture-amorphous coatings with a very smooth surface. The h ardness and abrasion resistance decreased with the increase in nitroge n content. Pure Zr-B coatings are silver-greyish with metallic brillia nce but nitrogen changes the colour from dark grey or black at low con tents to interference colours in the amorphous state. Ellipsometric me asurements of the refractive index n and absorption coefficient k supp orted the results derived from electron microscopy, colour measurement s and mechanical testing. The transition point between the fine-graine d and fracture-amorphous structure lies in the range of f(N2) around 1 0 sccm. The black coating deposited with such nitrogen levels showed g ood corrosion and abrasion resistance combined with a satisfying hardn ess. In some cases, increasing the nitrogen content improved the corro sion resistance. In potentio-dynamic experiments, more positive free c orrosion and pitting potentials were demonstrated. However, in salt sp ray testing and immersion testing using an artificial sweat solution, no beneficial effect of high nitrogen additions was noticed. Zr-B-N co atings deposited with nitrogen flow values in the range 10-20 sccm off er an excellent choice for decorative purposes, owing to their dark gr ey or intense black colour and good corrosion resistance.