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. Therefore, different composite coatings were electroplated in the same bath with different particles concentrations. It’s to find the optimum concentration of the particles that 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 by using 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 results 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 towards the surface of the coating. The result of bending test shows that the functionally graded composite coating has 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 reveals that wear resistances of functionally graded Ni-Al2O3 is higher than that of ordinary distributed composite coating.