Electroless Nickel Layer Research Articles

SURFACE ALLOYING OF MILD STEEL BY LASER MELTING OF AN ELECTROLESS NICKEL DEPOSIT CONTAINING CHROMIUM CARBIDES

Abstract It is possible to realize surface alloys by laser melting an electroless nickel layer containing chromium carbide particles predeposited on a mild steel substrate. By this way the surface alloy is expected to have not only a high nickel content but also an important chromium content in order to improve the corrosion resistance. The presence of chromium in solid solution results from the dissolution or melting of the carbide particles. Typical laser solidification microstructures are obtained. Dendrites consist of an austenitic Fe-Ni-Cr solid solution and interdendritic regions are constituted by an eutectic mixture containing the same austenitic solid solution and complex Fe, Ni, Cr carbides and phosphides. In comparison with a surface alloy obtained by laser melting of an electroless nickel layer without carbide particles, the corrosion resistance was slightly improved in saline aqueous solutions. The limited effect was due to the fact that the final chromium content in the present experimental ...

Determination of the sputtering rate of electroless nickel layers with a glow discharge lamp

AbstractGrimm glow discharge spectrometry was used to analyse electroless nickel coatings on a steel substrate. Because of poor depth resolution at the coating/metal interface, it was necessary to determine the sputtering rate of the layer itself at different power settings and to calculate the sputtering rate per power unit. The penetration time for layers with different thicknesses was also determined for different power settings. By comparing sputtering rates per power unit, it was found that the best results were obtained if the penetration time was equated to the time needed for the nickel signal to reduce to half its original value.

Stress Corrosion Cracking of Electroless Nickel‐Plated Low‐Carbon Steel in Hot Concentrated NaOH Solutions

The stress corrosion cracking (SCC) behavior of electroless nickel (EN)‐plated, low‐carbon steel (LCS) in boiling concentrated sodium hydroxide solutions has been studied. The effects of concentration and heat‐treatment of the EN layer on the SCC susceptibility were evaluated by constant load tests, with an initial applied stress of 120% yield strength. The results of polarization curves showed that the anodic current densities of LCS with EN coating in hot caustic solutions were almost two orders of magnitude higher than those of bare LCS. Heat‐treatment at 400°C for 1h or 650°C for 4h, respectively, could enhance the passive current density of EN coatings in the environments studied. The present results also showed that the as‐plated EN coating improved the SCC resistance of the LCS in boiling 20 and 50 weight percent (w/o) solutions, while a detrimental effect (reducing the time to failure drastically) of the as‐plated EN coating was found in boiling 40% solution by promoting intergranular SCC of the steel. Heat‐treatment at 400°C for 1h or 650°C for 4h could further increase the SCC susceptibility of the EN‐coated LCS. Microstructural change, namely, recrystallization and grain coarsening, could be one of the main factors affecting the corrosion and cracking behavior of the EN‐coated LCS.

The Mechanism of Adhesion Failure of Plated Plastics in Corrosive Environments

The mechanism of adhesion failure of plated ABS and polypropylene (PP) plastics exposed to service conditions was determined. Adhesion failure, through the formation of blisters, proceeds by a corrosion mechanism which involves (a) the rapid lateral anodic dissolution of the thin electroless nickel layer at the plastic‐metal interface or (b) the relatively slower preferential dissolution of an electroless copper layer and the equally reactive adjacent electrodeposited copper layer. The rate of lateral development of blisters is related to the surface topography of the etched plastic substrate. The high‐density crack patterns and surface roughness of etched PP provide a greater path length for the anodic dissolution of the thin electroless nickel layer— thereby retarding the lateral undercutting more than with a plastic which has a relatively smooth etched surface (ABS). When the less reactive electroless copper is present in a copper‐nickel‐chromium system, the plastic substrate surface topography has no effect on the lateral rate of blister development. The weaker tendency toward blister formation is due to preferential corrosion of the relatively thick, two‐layered copper deposit.