Mechanical,thermal and tribological properties of electro- and chemodeposited composite coatings

By means of chemical (autocatalytic) and electrolytic codeposition of nickel and silicon carbide particles it is possible to produce coatings with enhanced wear and corrosion resistance on metallic and plastic substrates.In the first part of the paper the basic plating technique in relation to the type, form, grain size and activation of the SiC particles will be described.The mechanical properties of the coatings depend on the amount of incorporated particles in the nickel matrix. By activation of the SiC powder the content of particles in the coating can be increased significantly. Mechanical properties such as hardness, strength and elastic modulus improve with increasing content of particles. It will be further shown that the negative influence of a pure nickel coating on fatigue is reduced with a coating of NiSiC. This result can be explained by the behaviour of the internal stresses in the coating as a function of the SiC content. The tribological properties of the coatings were tested by an abrasive wear mechanism under lubricated conditions combined with corrosion. The corrosive wear tests were performed under potentiostatically controlled conditions.The high temperature application of these coatings is limited by the thermal decomposition of the SiC particles in the nickel matrix at about 500 °C. The coatings were examined by various techniques such as differential thermal analysis, X-ray diffraction and secondary ion mass spectrometry. The influence of different temperatures on the mechanical and tribological properties of the coatings will be described.