The Electrochemical Corrosion of Bulk Nanocrystalline Ingot Iron in Acidic Sulfate Solution

Abstract

The corrosion properties of bulk nanocrystalline ingot iron (BNII) fabricated from conventional polycrystalline ingot iron (CPII) by severe rolling were investigated by means of immersion test, potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS) tests, and scanning electron microscopy (SEM) observation. These experimental results indicate that BNII possesses excellent corrosion resistance in comparison with CPII in acidic sulfate solution at room temperature. It may mainly result from different surface microstructures between CPII and BNII. However, the corrosion resistance of nanocrystalline materials is usually degraded because of their metastable microstructure nature, and the residual stress in nanocrystalline materials also can result in degradation of corrosion resistance according to the traditional point of view.

Corrosion of Ultrafine Grained Materials by Severe Plastic Deformation, an Overview

“…A) As the most simple structure, a various kind of pure metals of high and commercial purity such as aluminum, [87][88][89][90][91][92][93][94] copper, 6,37,[95][96][97][98][99][100][101][102][103][104][105][106] iron, 76,107) titanium, [108][109][110][111][112][113][114] magnesium, 34,72,[115][116][117] have been processed by SPD for corrosion studies. In this simple system, grain size or grain boundary density impacts the corrosion resistance as a primary metallurgical variable with very few other metallurgical changes involved.…”

“…33) Higher charge-transfer resistance of passive lm are interpreted as higher stability of passivation in UFG materials using electron impedance spectroscopy (EIS) in aluminum. 88,90,92,120,121) copper, 95) magnesium, 83,122,123) steel, 76,107) stainless steels, 73,124) Mechanical adhesion of oxide lm can be stronger in UFG materials than in coarse-grain materials by, for example, pegging mechanism. 106) Purity of the metals also may in uence the effect of grain size on corrosion properties because it affects the degree of impurity atoms residing at grain boundaries.…”

“…[108][109][110]112,127,155,[184][185][186] Recently, other SPD processing emerged such as hydraulic extrusion (HE), 111) severe-or cryo-cold rolling. 45,75,76) These SPD processing generates UFG metals in bulk form, but in other processing, UFG or nanocrytallization can be achieved in the surface layer using high power shot blast, 78) ultrasonic peening, 77,79,80) surface mechanical attrition treatment (SMAT), [72][73][74] burnishing/brushing, [82][83][84] and friction stir processing (FSP). 85,86) Table 2 lists the papers reporting on the corrosion behavior of UFG materials by speci cally SPD.…”

“…76) Dehghani et al 47) reported polarization behavior of IF steels in the active region in a wide range of pH which was controlled by mixing 3.5%NaCl and 0.1 M H 2 SO 4 . Nanograined IF steels exhibited smaller corrosion current in a wide range of pH as a result of more protective surface layer.…”

“…Most of UFG materials in the list are pressed by ECAP, HPT, ARB as the core of SPD technology, but the recent emerging SPD for surface modi cation such as surface mechanical attrition treatment (SMAT), 21,[72][73][74] cryorolling, 75,76) high-power shotblast, [77][78][79][80][81] burnishing, [82][83][84] friction stir processing (FSP) 85,86) are included. However, nanocrystalline metals, which are fabricated by the so-called bottom-up approaches such as magnetron and DC spattering, powder consolidation by high-energy ball milling are excluded in this Better=Corrosion resistance increases with grain size reduction, Worse=Vise versa.…”