Protective Coatings on Carbon Steel

Abstract

The experimental research aim was to analyze the corrosion resistance of superficial layers obtained by electrical sparking on the steel carbon samples. The electrodes used in these processes being made from corrosive resistance materials (coper and nickel). Processing by electric sparking occurs through electrode material erosion (anode) with a transfer by erosion products on the superficial workpiece. Processing of the treated surface begins with approximation of electrode by sample and at critical interval, it triggers electrical discharge through impulses. It is often continuous and ends at the electrodes contact. At the contact surface of the electrodes appear areas strongly heated causing electrical erosion of the electrodes (sample and electrode). The predominant transfer of anode material (electrode) to the cathode (the sample) ensures the formation superficial layer. After it the discharge was complete, at very small time interval, start removal of the Anode by cathode, action which ends with the interruption of electric circuit due to the transfer of material and the thermal changes from discharge area, in the superficial processing of metallic materials with electric sparks, the superficial layer of cathode it changes its structure and chemical composition. The samples being immersed 285 days in static sea water at the environments temperature. Corrosion resistance in seawater of superficial layers obtained with copper and nickel electrodes was determined by gravimetrical method. The samples covered with thin layers immersed in the corrosive agent (sea water) were analyzed through optical microscopy using QX3 Intel Play microscope and through atomic force microscopy. Experimental results were compared for both the surface of the initial sample material (OL 37) and the surface of the samples covered with Cu and Ni layers. One of the conclusions is: the superficial layer obtained by electrical sparking using cooper and nickel electrodes proves a improved corrosion resistance to see water compared to the base steel, specially for long term tries, when the corrosion speed is stabilizing remaining almost constant. The second main conclusion is: the investigations through atomic force microscopy made on the samples tested for long term corrosion, accentuate the compact and homogenous surfaces areas, which had not permitted the corrosive agent to interact with the base material.also, the wave-mode images present the discontinuities of the superficial laid layers, which represent a possible access way in for the corrosive agent to the samples material.