Optimization of Electrodeposited Ni-Cr Composite Coatings by using Taguchi Design and Grey Relational Method

Abstract

In this investigation, the Nickel (Ni) – Chromium (Cr) composite deposits was developed from conductive type nickel plating bath through electrodeposition technique. The Cr particles concentration in bath were taken in three different proportions such as 10 g/l,20 g/l and 30 g/l and got deposited on the Ni plate. The design of experiment technique, L27 orthogonal array of Taguchi method was employed for conducting experiments with different combination of parameters and its level. The parameters taken into consideration were current density level, pH range, bath temperature, Cr concentration in bath and stirrer speed. The experiment includes the measurement of micro hardness, area fraction of Cr, mass of deposit and coating thickness of coated samples with variable input parameters. The main effects of process parameters and their influences on the responses were analyzed. The outcomes shows that Cr concentration in bath and pH range are the most significant parameters for better enhanced responses measured. Microstructure examinations were conducted to analyze Cr deposition in prepared Ni plates using optical metallurgical microscope, scanning electron microscope (SEM) micro images and Energy Dispersive X-Ray (EDX) spectroscopy studies. Furthermore, the decision-making procedure was carried out for maximization of multi-performance measured responses using grey relational analysis (GRA). The optimized plating parameters levels are found to be 4 A/dm2 for Current density, 2.5 for pH, 45˚C for bath temperature, 30 g/l for bath concentration and 300 rpm for agitation speed to have the maximum micro hardness of 1037 HV, 370 mg of mass of deposit, 42% of Cr particle area fractions and 112 µm of coating thickness. Subsequently the obtained optimal combination of process parameters was validated through confirmation experiment. The results shows that the confirmation test responses are well associated with predicted response values on the Ni-Cr coatings.