Study On The Fabrication And Properties Of Composite Chromium Plating

The chromium coatings were used widely because of its wear-resistance, high hardness and corrosion-resistance. To farther improve coating's wear-resistance and hardness, composite chromium coatings were prepared by composite electroplating using CrO₃, H₂SO₄ and SiC as starting materials, and the effects of technology parameters on coatings' microstructure and properties were investigated in this paper .Experiment results showed that stirring intensity, current density, plating temperature and particles concentration played great influence on the microstructure and properties of the composite coating. The following optimal technology parameters were obtained by comparing of microhardness: stirring intensity of 1.4 L/min, current density of 25A/dm² , plating temperature of 40℃ and grain density of 400g/L, composite coatings participated by above parameters were of excellent particle dispersion and properties.After activation and hydrophilic treatment, the surface properties and states of SiC changed, the hydrophobic SiC particles became hydrophilic and the microcosmic surface is coarse, this is propitious to particles deposition and wear-resistance of the coating. To adsorb rear earth ions fully, and increase surface charge, SiC particles should immerse in the solution containing rear earth for hours.The effects of mechanical stirring and air stirring on the preparation of Cr-SiC coating are very important and were studied. On the condition of mechanical stirring, SiC particles moved mostly along with the direction of stirring, the possibility for the SiC particles to embed in matrix is very small. But, with air stirring, the rising of SiC particles were facilitated by air bubble, the rising air bubble and the air bubble adsorbing the surface of SiC particles also can impulse the particles to hit the cathode. Cr-SiC composite coating was well prepared in this case.The wear mechanisms of Cr-SiC composite coating were investigated. In the condition of dry wear, because of the different crystal structure and properties between SiC and frictional pairs, the adhesion wear of pure chromium was poor than composite chromium coatings. Wear mechanisms of Cr-SiC composite coating were adhesion wear, abrasive wear and oxidation wear.