Small amounts of metal ions (Sn 2 + or Cu 2 + ) added to an electrolyte for Mn electrodeposition increase the metallic character of amorphous Mn coatings grown at high current densities. The codeposited oxygen decreases from 54 atom % to less than 7 atom %, while the codeposited Sn or Cu are below 1 and 3 atom %, respectively. The resulting amorphous coatings exhibit very different mechanical properties and better corrosion resistance than those of amorphous manganese coatings electrodeposited without metal ion additives.

Increased Metallic Character of Electrodeposited Mn Coatings Using Metal Ion Additives

Cu-Mn electrodeposition from simple sulfate electrolytes with the only addition of ammonium sulfate was studied under different current densities, at pH 2.6-2.8 and pH 6.4-6.6, and at different cupric ion concentrations. An electrochemical investigation of this Cu-Mn electrodeposition system was conducted by potentiodynamic methods and cyclic voltammetry. Electrodeposition was performed galvanostatically. Mn content in the alloy increased with increasing current density. Three types of coatings were obtained: spongy Cu-rich oxygen-containing films at low current density, crystalline Mn-rich coatings at intermediate current density (type I), and amorphous coatings at high current density (type II). At high pH (6.4-6.6), the composition of type I coatings could be controlled by adjusting the current density, while at low pH (2.6-2.8) composition becomes more controllable by varying the Cu 2+ concentration ([Cu 2+ ]). The optimal current density to obtain type I coatings is shifted upward with increasing [Cu 2+ ]. A Cu-rich interlayer is formed between the Cu-Mn film and the stainless steel substrate. The bulk of type II coatings is mainly composed of metallic Cu and Mn. Metal complexation equilibria with NH 3 can explain the influence of Cu additions on coating morphology and composition.

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Electrodeposition and Characterization of Sacrificial Copper-Manganese Alloy Coatings I. Electrochemical and Morphological Characterization

Dipartimento di Chimica, Materiali e Ingegneria Chimica OG Natta,O Politecnico di Milano,20131 Milano, ItalyManganese-copper alloys were pulse plated from a sulfate solution with the addition of ammonium sulfate at pH 67 Anelectrochemical investigation of the MnÐCu electrodeposition system was conducted by potentiodynamic methods The effect ofpulse-plating on cathodic efÞciency , m icrostructure, and crystallography of the deposits was analyzed and compared with theresults from continuous plating Pulse plated coatings with short off-time w ere characterized by an uniform and homogeneousmorphology , suitable mechanical properties, and low copper content !! 5 w t % "T he codeposition of copper prevented the phasetransformation of as-deposited ductile " -M n to the brittle and hard # -M n All the coatings exhibited a good sacriÞcial protectionfor steel in sulfate and chloride media© 2006 The Electrochemical Society  !DOI: 101 149/12216431 " All rights reservedManuscript submitted January 27, 2006; revised manuscript received April 28, 2006 A vailable electronically July 11, 2006

Pulse Plating of Mn–Cu Alloys on Steel

The structure and properties of electrodeposited Mn-rich Cu-Mn coatings were studied in order to assess their potential to provide sacrificial galvanic protection to steels. It is found that a small amount of codeposited copper can stabilize the ductile as-deposited centered tetragonal γ′ phase against roomtemperature recrystallization to the stable bcc α phase. The time to transformation is increasingly delayed with increasing copper content. Phase transformation of crystalline films does not follow the Johnson-Mehl-Avrami-Kolmogorov equation for nucleation and growth transformation. Amorphous coatings do not show any structural transformation at room temperature. Nanomechanical and tribological measurements showed that Cu-Mn coatings have a lower friction coefficient than reference Cd coatings. Cu codeposition reduces the coating’s hardness and elastic modulus and increases the resistance to plastic penetration with respect to pure Mn. Cu-Mn coatings show a barrier or passive behavior under anodic polarization, while the sacrificial characteristics are still preserved. The corrosion appears uniform, and the formation of MnO2 and Cu2O upon anodic polarization may account for the good corrosion performance of the coatings.

Electrodeposition and characterization of sacrificial copper-manganese alloy coatings: Part II. Structural, mechanical, and corrosion-resistance properties

Pulse plating of manganese–copper alloys from a sulphate solution with the addition of ammonium sulphate at pH 6·7 has been studied. The Mn–Cu electrodeposition system is characterised by steady st...

Pulse plating of sacrificial Mn–Cu alloys from sulphate bath

Ni-Mn-Fe alloys were electrodeposited from three compositionally altered Ni-Mn electrolytes containing a small amount of FeSO 4 (NH 4 ) 2 SO 4 .6H 2 O (10gl -1 ). Texture development in the resultant co-deposits was investigated with opticical colour polarisation microscopy. Addition of Fe in the electrodeposited Ni-Mn system results in the development of additional textures. Most of the samples show three different types of textures though the texture types are characteristic of the bath composition and deposition CD.

M. V. Ananth

Papers

Texture Development in Electrodeposited Nanocrystalline Ni-Mn-Fe Alloys