Corrosion Behavior of Severely Deformed Pure and Single-Phase Materials

Abstract

The significant and complex effect of plastic deformation on corrosion behavior involves changes in not only dislocation density but also other metallurgical factors such as grain size, texture, chemical inhomogeneity, phase transformation and residual stress. With the advent of severe plastic deformation (SPD), the effect of plastic deformation on corrosion in the ultrahigh strain range is becoming an important issue. However, our understanding of corrosion properties of SPD materials lags far behind than that of their other properties, e.g. their mechanical properties. In this review, the role of dislocations and grain boundaries generated by SPD was highlighted in pure metals and single-phase materials, where plastic deformation and grain refinement proceed mainly by dislocation activity. Accordingly, the complicated effect of chemical inhomogeneity arising from impurity segregation and precipitation was excluded from discussion, while other implicit effects were included. It is essential to elucidate the effect of so-called ultrafine-grained (UFG) structures which develop progressively to a saturation over a very wide strain range. Unfortunately, the literature mainly compares the corrosion behavior of UFG and coarse-grained (CG) materials, and the degree of perfection of UFG formation and the resultant effects on corrosion vary between studies. The limited number of studies that examines corrosion behavior systematically over a wide strain range suggests that, in most cases, the effect of plastic deformation on corrosion extends into the SPD region gradually, with no anomalous change. That is, SPD improves the corrosion resistance to further degree in a passive environment, whereas it increases the dissolution rate in a non-passive environment. However, several works reported an abrupt change in corrosion resistance, which could be attributed to UFG formation. A marked improvement is observed in FeCr alloys, where passivation becomes more protective owing to UFG formation induced by SPD. In severely deformed materials, structural alterations in dislocations and grain boundaries have a very high impact on the corrosion kinetics because of their closely spaced configuration.

Nanostructured Bulk Titanium with Enhanced Properties—Strategies and Prospects for Dental Applications

“…[70] The nonequilibrium grain boundaries demonstrate almost double the energy of equilibrium ones. [33,75] We propose grain boundary equilibration as the probable reason for the enhanced corrosion resistance of nano Ti after short-term annealing. However, the probable enhanced potential difference between the grain boundaries and grain interiors, which are virtually free of dislocations, may be the reason for slightly lower corrosion resistance after extended heat treatment.…”

“…[31] UFG/nano Ti products obtained by large plastic deformation methods demonstrate both superior mechanical properties and higher corrosion resistance compared with microcrystalline CP-Ti. [32,33] Mott-Schottky tests demonstrated that the passive layer formed on the nano Ti surface in simulated physiological conditions is less defective than micro CP-Ti. [7] Moreover, the huge number of structural defects in nano and UFG Ti is expected to accelerate the passivation (Figure 2) and repassivation process after damage to the oxide layer, which may be induced by tribocorrosion phenomena.…”

Corrosion Behavior in Hank's Solution of a Magnesium–Hydroxyapatite Composite Processed by High‐Pressure Torsion

“…In fact, the whole surface of the sample gradually becomes covered by corrosion products which shows a more general type of corrosion after long immersion times. A pseudouniform type of corrosion has been suggested in ultrafine‐grained materials [ 28,29 ] and earlier reports showed essentially uniform corrosion in ultrafine‐grained pure Mg. [ 3,4 ] It is interesting to note that the addition of HA fails to change this behavior despite the potential for forming galvanic cells in a composite.…”

A New Method of Edge Crack Suppression in the Rolling Process of Magnesium Alloy Sheet and Study on the Method of Cathodic Protection

“…Based on this, the new concept of thermal insulation rolling table equipment and edge crack suppression for the magnesium alloy is put forward in this paper. Combined with the study of cathodic protection, the method realizes to suppress edge crack and hydrogen corrosion [44,45] in rolling process of the magnesium alloy plate and effectively improve the forming quality of the magnesium plate [46].…”