Electroless Deposition of Ni-P Composite and Multilayer Coatings: Applications and Perspectives

Abstract

Considerable economic losses occur every year due to erosion-corrosion in parts of machines and equipment during service. In order to reduce this loss, properties of the surface of the materials should be improved. Among the various surface processes, electroless plating is one of the appropriate methods to deposit coatings on metals without applying an external electrical voltage, which provides coatings with uniform thickness, crack free nature, appropriate adhesion to the substrate, high hardness, and high wear resistance. The electroless deposition is a promising method to prepare durable metal films on both conducting and non-conducting substrates of different geometries. In the present study, Ni-P composite coatings were successfully electroless plated on mild carbon steel from acidic baths reinforced with ceramic and polymeric micro and nano-particles, as single and multilayer deposits. The effect of the electrolyte composition as well as the nature of the dispersed phase on the phosphorus co-deposition, particles incorporation, surface morphology and structure of the deposits have been investigated and evaluated. The use of multilayer or hybrid techniques in surface engineering has often been cited as the way to improve the mechanical, tribological and electrochemical properties of coatings. Especially, the multilayer coating with layers having different corrosion potential Ecorr was an effective solution to improve the corrosion-resistance of the no-sacrificial coatings. Multilayered coatings were produced by stacking layers of different composition by successive electroless plating with rinsing steps in between. This study will discuss new applications and perspectives of these coatings as anti erosion-corrosion surface treatments. The impact of the plating approach on the microstructure of the coatings as well as on their mechanical properties and corrosion resistance is presented.