INVESTIGATION OF OXIDATION RESISTANCE OF NI- TI ELECTROCHEMICAL CODEPOSITION COATING OF AUSTENITIC STAINLESS STEEL (316 L)

The effects of Ti particle loading in a plating bath on the morphology and hardness of Ni-Ti composite coatings via an electrochemical codeposition coating were investigated. The Ti-reinforced Ni-matrix composite coatings were codeposited on Austenitic Stainless Steel (316 L) substrates using a Ni-ion electrolytic solution stably suspended with -20 ?m max. diameter Ti particles and heat treated under vacuum atmosphere for six hours at 950 °C prior to oxidation testing. During heat treatment, coating morphological development was found to occur by the exothermic reaction Ni +Ti = NiTi. Further, the oxidation behavior of nickel matrix/ titanium particle composite coatings in air at (700-900°C) for 50 hrs. was studied. The prepared coatings were characterized by X-ray diffraction (XRD), optical microscope, scanning electron microscopy (SEM), Vickers hardness, and atomic absorption. For all samples, weight gain kinetics was obtained from furnace exposure and the composition and morphology of the oxidation products were examined using XRD analysis and optical microscopy. An outer TiO2 layer was formed on the composite coating surface. At test temperatures 700, 800, and 900 °C, the coatings benefits from a small grain size that enhances Ti diffusion to the surface to form the protective TiO2 layer.