A study on hardness of nickel-based cermet coatings composed of α-Al2O3 and TiO2 nanoparticles

Nanostructured ceramic-metallic (cermet) coatings composed of one or two types of nanosized ceramic particles (alpha-Al2O3 and TiO2) dispersed in a nickel matrix were produced using co-electrodeposition method. This research investigated the effects of alternating the concentration of ceramic particle in the electrolyte solution and applied current density on the microstructure, volume fraction of deposited particles in the nickel matrix and the microhardness of the coatings. The results showed that both alpha-Al2O3 and TiO2 were uniformly distributed in the nickel matrix and the volume fraction of deposited ceramic particles in the matrix increased when the concentration of particles in the electrolyte was increased. Similarly, when higher current densities were applied, the volume fraction of deposited particle in the nickel matrix was increased to a maximum value of 12.6%. The results also showed that coatings with greater volume fraction of alpha-Al2O3 particles in the nickel matrix tend to have greater microhardness compared to the coatings with greater volume fraction of TiO2 and when both type of ceramic particles were incorporated in the nickel matrix, the microhardness of coatings corresponded to the ratio of the ceramic particles concentration in the electrolyte solutions. The increase in microhardness of the cermet coatings produced in this study was attributed to a combined effect of dispersion-strengthening of ceramic particles in the Ni-matrix as well as grain refinement of the nickel matrix.