Metal Matrix Composites as Environment-Friendly Protective Coatings

Protective coatings able to provide improved tribological behavior and corrosion resistance are demanded in many industrial applications. Although hard chrome is a very effective solution and is widely used, environmental issues related to hexavalent chromium push to develop alternative treatments. Within the framework of the HardAlt European Project, electrodeposited composite coatings have been developed and main results of this investigation are reported in this work. Boron carbide micro-particles were dispersed in a Ni-P matrix under different operating conditions, in order to produce coatings with different composition and particle content. Structural and morphological characterization was performed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Mechanical properties were evaluated by micro-indentation and the tribological performance was assessed by block-on-ring tests. Electrochemical experiments were carried out to examine the corrosion behavior of the composite coatings. Interesting results were obtained for composite coatings as regards hardness values, tribological behavior and corrosion resistance, even though some improvements can be realized. However, the results presented in this work show that composite coatings may represent a promising alternative to hard chrome for selected applications and also suggestions for further investigation are gained.