Effect of Pretreatment on the Properties of Electroless Nickel Phosphorios Coating

The autocatalytic (electroless) deposition of Ni–P based alloys is a well-known commercial process that has found numerous applications because of their excellent anti-corrosive, wear, magnetic, solderability, etc,… properties. It is a barrier coating, protecting the substrate by sealing it off from the corrosive environments, rather than by sacrificial action. The corrosion resistance of Ni-P coating is affected by its thickness, phosphorous content, adhesion, microstructure, etc. In this study, the influence of mechanical polishing pre-treatments on steel substrates is investigated in terms of microstructure, deposition rate, adhesion, electrochemical and corrosion properties of electroless Ni-P nano coatings with 9-10 wt. % P content. XRD analysis of Ni-P coatings demonstrated the nanocrystalline structure of coatings with grain size of 39 nm. Results showed that pretreatment of substrate can affect the microstructure and nodularity of coatings. Coating with the lowest nodularity have the highest mechanical and electrochemical resistance due to the absence of nodule boundaries. Results also showed that roughness of coating increased with increasing the roughness of substrate and with decreasing the substrate roughness adhesion of coating decreases.

Keywords:

Electroless , Ni-P nano coating , Corrosion , Surface preparation