Effect of saccharin addition on the microstructure of electrodeposited Fe-36 wt.% Ni alloy

Pulse current electrodeposition of Fe-36 wt.% Ni (Invar alloy) was carried out to investigate the effect of saccharin on the microstructure of the electrodeposited films. Electrodeposition without saccharin in electrolyte gave burnt and torn deposits, due to the very high internal stress that developed during electrodeposition. With a saccharin concentration less than 3.0 g/L in electrolyte, the surface of the electrodeposit was smooth and bright with a uniform thickness. The deposits were composed of FCC and BCC mixed phases and an FCC phase having nanosize grains, in which the {111} and {200} preferred orientations were predominant. With a saccharin concentration of more than 4.5 g/L, however, the surface became rough and dull with an appearance of faceted islands. This structure was related to the development of a (200) fiber texture in the BCC phase. Based on TEM observation, it was found that some BCC grains grew to microsize, while the FCC grains remained as nanosized. Dominant growth of the BCC grains is related to stress relaxation by slip deformation.