Ni-SiC composite coatings were electroplated from a nickel sulphamate solution with a SiC suspension, with and without the addition of monovalent thallium ions. Without thallium ions, the incorporated SiC particles did not modify the columnar grain structure of the nickel matrix. Conversely, the nickel matrix exhibited an equiaxed grain structure; meanwhile, the amount of codeposited SiC was markedly increased by adding thallium ions to the solution. Additionally, the density of lattice defects associated with nickel grains substantially decreased when the columnar grains were replaced by equiaxed grains. These distinct grain structures associated with the various coatings were discussed in terms of the inhibition of nickel electrocrystallization by thallium ions as well as the absorption and reduction of the various ionic species absorbed on the surface of the SiC particles.