Influence of saccharin sodium on microstructure and performance of electrodeposited nanocrystalline Ni coating

Nanocrystalline nickel (nc-Ni) coatings were prepared by pulse electrodeposition method. Their microstructure was investigated by SEM, TEM and XRD, and their microhardness, thermal stability and corrosion resistance were studied by a microhardness tester, DSC and potentiometer, respectively. It is found that with the increase of concentration of saccharin sodium (C₇H₄NO₃SNa · 2H₂O) the grain size of nc-Ni coating decreases firstly, and then increases, while the smallest grain size is achieved at 10 g/L. With the saccharin concentration less than 15 g/L in electrolyte, the surface of the electrodeposit is smooth and bright. The microhardness of nc-Ni coatings reaches the maximum when the content of C₇H₄NO₃SNa · 2H₂O is 10 g/L. The relationship between the grain size and microhardness fits for the Hall-Petch function approximately. The instability growth temperature of nc-Ni coatings is slightly fluctuated at 305°C under different content of C₇H₄NO₃SNa · 2H₂O. The corrosion resistance of nc-Ni coatings is optimum when the content of C₇H₄NO₃SNa · 2H₂O is 10 g/L.