Characterization of anomalous Fe-Ni alloy coating by electrodeposition and its properties

Abstract

Iron-nickel (Fe-Nil alloys are of great commercial interest as thcy possess low thennal cxpansion, soft mab'llctic and widc spectrum of physical properties. Attcmpts have been made to explain the anomalous mechanism of Fe-Ni alloy codeposition and researchers have proposed several models. Main focus of this work is to invcstil':ate the enect and the inlefaction of complexinl': agenl~ on the propertics of electrodeposited Fe-Ni alloy coating as well as the special characteristic of anomalous natlll"e. The Fe-Ni films were deposited from eight different baths; two of them were simple, coutaming NIS04, Fe504, Na1SO., H,BO.l as main ingredients and another six were complex, containiug ascorbic acid, saccharin and citric acid as complexing agent along with the main ingradicllls in varying compositiou. Fe-Ni alloy coatings were etectrodepositcd on Cu substrate at room tcmperature in the cum:nt density raub'e of20- 140 mNcml. Th", effects of current density, pH and bath composition on the coating appearance, composition, hardness, corroSIon resistance, morphologies and magnetization were studied. Chemical analysts, Mil..-TOhardness,Corrosion resistance, M0'Phologics and Magnetization of the coatings were studied by means of Conventional Wet Method, Mierohardness Tester, Salt Immersion Test, Scanning Electron Microscope (SEM) and Vibrating Sample Magnetometer (VSM) respectively. It was observed that coating obtaliled al higher cllrrent denSity with higher bath pH was blackish (examined with naked eye) while lower current density with higher pH or h'gher current density with lower pH resulted In uniform and bright coatings. The Ni percentage of the coating as well as its VHN increased with increasing current density for SImple baths but the reverse situations occurred for complex baths. Addition of complexing agents suppresscd the anomalous characteristics of the Fe-Ni alloy eJectrodeposition. The corrosion rate decreased with increasing Ni content of the films. Formation of protective NiO layer is supposed to inerease the corrosion resistance of high Ni content thin film Thus, the properlle~ of electrodeposited Fe-Ni alloy are strongly influenced by the electrolytic composition and deposition parameters. Tile filtn 7 obtained from simple baths did 1I0t exhibit smooth surface and the coating developed sharp line microcracks due to the internal stress developed during depositlOn in it. No cracks were observed and the coating gram size became finer for the coatings from complex baths compared to the simple baths. A clear morphological modification was observed due to the addition of eompJexing agent. The saturation magneti£ation of the electrodeposited Fe-Ni coating was fOlmd to decrease with increasing Ni content which is in good agreement with suppression of ferromagnetic character of the films. The highest saturation magneti7<1tionwas seen 131.13 cmwg among the coatings studied which is very close to the acceptable limit (135 emu/g). Charactenzatioll of Fe-Ni alloy plating parameters with its properties was attempted.