Structure Characterization and Parametric Evaluation of Low Phosphorus-Nickel Alloy Electroless Deposits

Abstract

Nanocrystalline nickel-phosphorus (Ni-P) deposits were synthesized by electroless deposition on mild steel. The samples were degreased and pre-treated before starting the deposition process. The Ni-P was deposited on the samples by placing the mild steel substrate in the neutral plating bath at 85-90⁰C for 90 minutes. The surface morphology of the coating was analyzed using Scanning Electron Microscopy. Energy Dispersive X-ray Spectroscopy was used to estimate nickel and phosphorus in the foil. Analysis of thickness and hardness was performed manually using a formula and by Vickers microhardness tester, respectively. Differential Scanning Calorimetry (DSC) was used to determine the temperature for phase transformation. A wear test was done to determine the effect of coating on the Coefficient of Friction (COF) of the substrate. The thickness of the Ni-P deposits was in the range of 31.71 µm to 34.88 µm when plating was carried out for 90 minutes. It was found that the synthesized samples had a nanocrystalline structure because of low phosphorus content and the hardness of the sample was increased by 22.21% with heat treatment. During phase transformation, the nanocrystalline structures were converted into crystalline form. The COF was decreased for the electroless Ni-P-coated mild steel in comparison to the uncoated mild steel substrate. However, the heat treatment improved the wear property (20 to 10 microns) and the COF (0.19 to 0.12) in the coated substrate.