Metal matrix/metal particle composite coatings were deposited, heat treated and characterized. A nickel matrix/aluminum particle coating deposited from a sulfamate bath was chosen as a model system. By varying the process parameters, up to approximately 20 vol.% Al particles were incorporated into the coatings. Based on light optical and scanning electron microscopy, a schematic model is presented for coating morphology development during codeposition of small, electrically conductive particles. For high deposition current densities, the hardness of the as-plated Ni-Al coatings was higher than that of pure Ni coatings due to the nucleation and growth of small Ni grains on the surface of the Al particles. This structural refinement leads to Vicker's hardness of about 350-400 HVN (25 g load) for Ni-Al coatings compared to about 200-250 HVN (25 g load) for pure Ni coatings deposited under similar conditions.