Influences of Al and Ti particles on microstructure, internal stress and property of Ni composite coatings

Abstract

Ternary Ni—xAl—yTi (x, y in weight percent) composite coatings with different amounts of mixed Al and Ti particles were prepared by electrodeposition. The influences of particles on the microstructure, internal stress and properties of coatings were comprehensively studied. In all coatings, the stress gradually increased along depth from bottom layer to top layer and the compressive stress transformed to tensile stress accordingly. At the same depth layers, the internal stress of different coatings gradually increased with increasing mixed particles in coatings. The increase of internal stress could be ascribed to crystallite refinement and attenuation of [200] preferential growth orientation of Ni deposits, which resulted from the co-deposition of particles. Through HR-TEM analysis, the amorphous layers composed of O and Al were found on the surface of Al particles, weakening effects of Al particles on stress distribution in coatings. The Ti surface could cause severe lattice mismatch between Ti and nickel crystallites, increasing interface stress and Ni twin crystals near Ti particle. However, the amorphous layer reduced the lattice mismatch, interface stress and twin crystals of Ni deposits near Al particle. The co-deposited particles enhanced corrosion resistance and micro-hardness of coatings due to the amorphous layers on Al particles and microstructure changes of Ni deposits.