Electrolytic co-deposition of carbon nanoparticles with metals, improvement of corrosive and mechanical properties

Main idea of this study is to fabricate chromium-carbon black composite coatings by electro-codeposition system and to obtain metal-ceramic composite structures with additional heat-treatments. These heat-treatments were aimed to realize in-situ phase transformations. The composite structures referred were electro-codeposited in sulfuric acid based solutions containing nano/submicron sized carbon black particles. The effect of heat-treatment conditions on the in-situ carbide phase formation in the chromium matrix composite coatings, and their corrosion and mechanical behaviors were investigated. The obtained results showed that the chromium-carbon composite coatings can be fabricated successfully by this technique and with an additional heat-treatment; it is possible to obtain a chromium-chromium carbide and/or chromium nitride composite structure on steel substrates. The coatings were compared with respect to the conventional hard chromium coatings. In regard to the electrochemical behavior, the chromium-carbon black composite coatings heat-treated under nitrogen atmosphere at 800oC showing a rehabilitated crack-free microstructure, exhibited better corrosion resistance than the conventional hard chromium structures. Therefore, the increase in corrosion potential suggests improvement of corrosion resistance due to the formation of chromium carbide/chromium nitride. Characteristic properties such as hardness and modulus of elasticity were determined for carbide and nitride formed composite coatings. It was observed that the following phase transformations support the recovery of friction-wear characteristics and accordance of substrate-coating interface belonging to the material. According to the detailed inspections, it was assigned that the definite results are directly correlate with both the magnitude and the direction of the residual stresses. All the excellent results obtained implies that the chromium matrix-carbide and/or nitride reinforced composite coatings have potential application to industrial fields in many respects. Keywords: Hard chromium, nanocomposites, corrosion, mechanical property