L. Sziráki

Electrochemical behavior of electrodeposited strongly disordered Fe-Ni-Cr alloys

Potentiodynamic and chronoamperometric polarization measurements, 57Fe conversion electron Mossbauer spectroscopy, X-ray diffractometry and electron microprobe measurements were performed on amorphous and microcsrystalline Fe–25Ni–25Cr alloys coatings electrochemically deposited at varying times in comparison with a thermally prepared alloy of the same composition. Significant differences were found among the Mossbauer spectra of electrodeposited alloys reflecting differences in the short range ordering of the dominant ferromagnetic phases. The potentiodynamic polarization curves revealed a higher ability to spontaneous passivation for the more disordered deposit while anodic dissolution was characteristic for the more ordered electrodeposits and for the crystalline thermally prepared alloy. The onset of the passivation of amorphous alloy was enhanced either by the decreased anodic dissolution or the increased hydrogen evolution rate. At the early stage of passivation, consistent passivation characterization was found both by chronoamperometric and potentiodynamic curves and by polarization resistance measurements performed at open circuit potential.

Mössbauer Investigation of Electrodeposited Sn–Zn, Sn–Cr, Sn–Cr–Zn and Fe–Ni–Cr Coatings

Abstract57Fe and 119Sn CEMS, XRD and electrochemical measurements were used to investigate the effect of the preparation parameters and the components on the structure and phase composition of electrodeposited Fe-Ni-Cr alloys in connection with their corrosion behavior. XRD of the electrodeposits reflect an amorphous-like character. 57Fe CEM spectra of Fe-Ni-Cr electrodeposited samples, prepared in a continuous flow plating plastic circulation cell with variation of current density, electrolyte velocity and temperature, can be evaluated as a doublet associated with a highly disordered paramagnetic solid solution phase. This phase was identified earlier in Fe-Ni-Cr electrodeposits that were prepared by another plating method and contained both ferromagnetic and paramagnetic metastable phases [1]. This is the first time that we have succeeded to prepare Fe-Ni-Cr alloys containing only the metastable paramagnetic phase. The effect of the plating parameters on the structure is also analysed by the quadrupole splitting distribution method. 119Sn CEM spectra of all Sn-containing plated alloys show a broad line envelop which can be decomposed at least into two components. One can be associated with β-tin. The other one can be assigned to an alloy phase. The structure and distribution of microenvironments of these phases depends on the plating parameters especially on the parameters of the reverse pulse applied.

Mössbauer, x-ray diffraction, and microscopy investigations of novel electrodeposited amorphous alloys

New Sn-Fe binary, Sn-Co-Fe, and Sn-Ni-Fe ternary alloys were successfully deposited from an electrolyte based on sodium gluconate. X-ray diffraction and 57Fe and 119Sn Mossbauer results confirmed the existence of new metastable amorphous ferromagnetic and paramagnetic alloy phases within these deposits. It was possible to find deposition conditions at which the amorphous alloy phase was found to be a dominant phase for all the electrodeposits investigated. A nearly random distribution of alloying elements may be considered as a model of short-range order in the amorphous phases.

Characterization of the passive films on electrodeposited Fe-Ni-Cr alloys in borate solution at pH 8.4

The corrosion properties of the passive layers formed on iron-nickel-chromium electrodeposits of Fe29Ni51Cr20 were investigated in 0.3 M borate solution at a‘ pH of 8.4. On the basis of measurements by cyclic voltammetry, chronopotentiometry and electrochemical impedance spectroscopy, a low passive dissolution/corrosion rate was identified for the electrodeposited Fe-Ni-Cr alloys due to the nature of the established corrosion layer. The stability of this passive layer was further enhanced after corrosion under oxidizing conditions. Mössbauer spectroscopic measurements confirmed the existence of a thin passive layer on the amorphous electrodeposits.