A COMPARISON OF DC AND PULSED FE-NI ALLOY DEPOSITS

The effect of hydrodynamics and temperature on the electrodeposition of Fe-Ni alloys has been investigated with dc, pulse, and pulse-reverse electrodeposition techniques. Strong mass-transfer effects in the co-deposition of Fe on rotating cylindrical cathodes were indicated at high current densities. Many features of the present deposition process are shown to be consistent with the Hessami and Tobias model. A comparison of the polarization behavior of single-metal and alloy deposition clearly demonstrate the lower rate of Ni co-deposition in accord with previous reports of anomalous co-deposition of Fe-Ni alloys. X-ray diffraction studies indicate that the crystalline phases (fcc, bcc, and mixed fcc + bcc) in the electrodeposited alloys depend on alloy composition and deposition conditions. Thermal expansion coefficients of electro-formed cylinders of near-Invar compositions ranged from 7.7-10.9 x 10(-6)/degrees-C for unannealed alloys to 4-5 x 10(-6)/degrees-C for alloys annealed at 680-degrees-C. Average internal stress of deposits increased with increasing Fe content.