Optimization of process parameters using central composite design and Taguchi method to improve hardness in ENi-B coatings: A comparative approach

Abstract

Electroless nickel boron (ENi-B) coatings have been used in various applications because of their high hardness and wear resistance characteristics. In this study, the independent variable concentrations of nickel, reducing agent and stabilizer, influencing the hardness of the deposits was optimized by central composite design (CCD) of response surface methodology (RSM) and Taguchi technique (TT). Taguchi L9 orthogonal array (OA) was employed to develop the experimental runs. The optimum process parameters were identified by utilizing the signal-to-noise (S/N) ratio computed for the hardness as per ’’the-larger is better” approach. From the response table for S/N ratio, it was identified that reducing agent’s contribution was more for the hardness of the ENi-B deposit, when compared to the nickel ion and stabilizer concentrations. From CCD the optimum source of nickel ion, stabilizer and reducing agent concentrations were found to be 29.92, 31.63 and 0.78 g/L with the maximum hardness of 591 HV. The optimum values were confirmed by the experiments, the maximum hardness achieved between CCD and TT did not show a significant variation in hardness. Therefore, it is concluded that CCD may be more promising in identifying the response, by developing a mathematical model that directly relates the process parameters and hardness over the Taguchi technique.