Characterization of Co-Electrodeposited Functionally Gradient Ni-Al2O3 Composite Coating

Abstract

For the first time, functionally Al₂O₃ content graded Ni-Al₂O₃ composite coating has been successfully co-electrodeposited from a bath with gradually increasing stirring rate. For this, different composite coatings were electroplated in the same bath with different stirring rates to find the optimum stirring rate in which the maximum content with uniform distribution of Al₂O₃ particles in the coating can be achieved. To produce Al₂O₃ content graded Ni-Al₂O₃ composite coating, the stirring rate was continuously increased from 0 to optimum value. By increasing of Al₂O₃ particles content, the microhardness increases from interface towards the surface of the coating. The results of wear resistance measurements and potentiodynamic polarization test revealed that wear and corrosion resistances of functionally graded Ni-Al₂O₃ (FGNA) is higher than that of ordinary Ni-Al₂O₃ (ONA) composite coating. This result has been attributed to lower mechanical mismatch between coating and substrate in the functionally graded composite coating with respect to the uniformly distributed one.