THE MORPHOLOGY AND STRUCTURE OF SOL-GEL DERIVED ZIRCONIA FILMS ON STAINLESS-STEEL

Sol-gel zirconia films of various thicknesses were deposited on 316 st ainless steel and treated using one of two firing regimes. The resulti ng effect on the structure of these films was investigated. One set of films were fired using a regime typically employed for thermal barrie r coatings, in which each layer was dried at 380 degrees C separately and then the whole film, which consisted of up to 12 layers, was fired to 800 degrees C. A second set of films were prepared by drying and f iring each layer in turn following each deposition. Atomic force micro scopy and scanning transmission electron microscopy revealed that the former firing regime was detrimental to the film morphology, resulting in cracking and delamination of the films. These films were also foun d to contain a significant amount of residual carbon before their fina l firing. Removal of this carbon during the final firing causes shrink age and induces tensile stress in the film, The morphology of the latt er set of films was found to be crack-free and possessed a surface whi ch became smoother with increasing film thickness, All films were foun d to contain a discrete layer of chromium oxide between the film and t he steel substrate. (C) 1997 Elsevier Science S.A.