Fabrication of functionally graded Ni-Al2O3 nanocomposite coating and evaluation of its properties

In this study, functionally graded Ni-Al2O3 composite coating (FGN-A) has been produced from nickel Watt’s bath containing different concentrations of Al2O3 particles. For this, different composite coatings were electroplated in the same bath with different particles concentration to find the optimum concentration of particles in which the maximum content with uniform distribution of Al2O3 particles in the coating can be achieved. So, Al2O3 concentration was continuously increased in the electroplating bath. The composite coatings were characterized by SEM and EDS. Structure and phase composition were identified by XRD analysis. Microhardness of the coatings was evaluated employing Vickers Instrument. Three-point bend test was carried out to compare the adhesion strength of the coatings and dry sliding wear tests were performed using a pin-on-disk wear apparatus. Study on the resulting sample shows that FGN-A by Al2O3 gradient distribution in cross-section is coated successfully. By increasing Al2O3 particles content in Ni matrix, microhardness grows from interface toward the surface of the coating. The result of bending test show that the functionally graded composite coating shows excellent adhesion to substrate compared with the uniformly distributed Ni-Al2O3 (UN-A) on the same substrate. This has been attributed to lower mechanical mismatch between coating and substrate in functionally graded composite coating compared with uniformly distributed one. The results of wear resistance measurements test revealed that wear resistances of functionally graded Ni-Al2O3 is higher than that of ordinary distributed composite coating.