Optimization of Electroless Ni–P–Al2O3 Composite Coatings based on Multiple Surface Roughness Characteristics

Electroless Ni–P–Al2O3 composite coatings are popular due to their excellent hardness, friction and wear resistance. The present study tries to investigate the influence of coating process parameters on the surface roughness of electroless Ni–P–Al2O3 composite coating with the help of Taguchi analysis. The different surface roughness parameters considered are, center line average roughness (Ra), root mean square roughness (Rq), skewness (Rsk), kurtosis (Rku), and mean line peak spacing (Rsm). Three parameters, namely, concentration of nickel sulphate as a nickel source, concentration of sodium hypophosphite as reducing agent, and concentration of Al2O3 particles as concentration of second phase particles are considered and fitted into an L27 orthogonal array to find out the optimized condition to minimize the surface roughness of the coating. It is observed that concentration of Al2O3 particles have the most significant influence on Ni–P–Al2O3 composite coating and concentration of reducing agent has moderate influence. The compositional, micro-structural, and phase structure analyses are conducted with the help of energy-dispersive X-ray analysis, scanning electron microscope, and X-ray diffraction analyzer, respectively.