Characterization of electroplated Ni/SiC and Ni/Al₂O₃ composite coatings bearing nanoparticles

Ultrafine SiC and Al₂O₃ particles with 30–50 nm sizes were used to codeposit with Ni in a sulfamate bath to form composite coatings. The microstructure and mechanical properties of the layers were investigated by x-ray diffractometry, scanning and transmission electron microscopy, high-resolution transmission electron microscopy, microindentation, and wear testing. The microstructural results revealed that 7 vol% of SiC or Al₂O₃ particles dispersed randomly in the Ni matrix. The addition of the ultrafine SiC or Al₂O₃powder into the Ni matrix apparently reduced the size of Ni grains during the electroplating and inhibited the grain growth during heat treatment. The microhardness and wear resistance were improved by the addition of SiC and Al₂O₃ particles, especially for SiC/Ni samples after heat treatment at 400 °C for 24 h. The mechanisms of hardening and wearing of Ni-based electroplated layers are discussed.