•Machine hammer peening (MPM) introduces smoother surface as well as nano-grains and nano-twins in the near surface region.•MPM leads to more severe work hardening and higher compressive residual ...stress .•MPM has a benificial effect on the corrosion resistance of nickel-base alloy 718.
The effect of surface modifications induced by machine hammer peening on pitting corrosion behavior of nickel-base alloy 718 in a 3.5wt.% NaCl solution is investigated. Severe work hardening and high compressive residual stress are generated with surface smoothing and microstructure evolution in terms of formation of nano-grains and nano-twins in the near surface region after machine hammer peening. Electrochemical tests results show that machine hammer peening has a beneficial influence on the corrosion resistance, indicated by a significant increase of the critical pitting potential (+134mV) accompanied with lower corrosion current density and higher polarization resistance.
•The initial stages of the pitting corrosion of Q460NH steel in a marine environment was studied.•Two different types of inclusions formed in the Q460NH steel after adding rare earth.•Both types of ...inclusions showed a lower Volta potential than the matrix.•Pitting corrosion was induced by the dissolution of inclusions rather than the matrix.•Inclusions containing (RE)AlO3 dissolved completely as a result of the acidic solution formed in the pits.
In this work the initial stages of the pitting corrosion in Q460NH weathering steel in a marine environment was studied. To elucidate the effects of inclusions modified by rare earth (RE) elements on pitting corrosion, field emission-scanning electron microscopy-energy dispersive spectrometry (FE-SEM-EDS) analyses, scanning Kelvin probe force microscopy (SKPFM) tests, and a series of immersion tests were conducted. Two main types of inclusions were formed in the steel, and different pit morphologies were observed. The pitting corrosion was initiated by the dissolution of (RE)2O2S-(RE)xSy in both types of inclusions due to the lower potential of this phase compared to the matrix, which indicated that the inclusions in the Q460NH weathering steel had a lower pitting corrosion resistance than the matrix.
A series of single phase Ni38Fe20CrxMn21–0.5xCo21–0.5x multi-principal element alloys (MPEAs) were fabricated and their localized corrosion behavior was tested in 0.6 M NaCl solution. These MPEAs ...were found to be susceptible to localized corrosion, exhibiting pitting at room temperature, as indicated by positive hysteresis loops and low repassivation potentials observed in cyclic potentiodynamic polarization experiments. The pitting resistance increased with increasing Cr content. Interestingly, even the MPEAs with low chromium content, Ni38Fe20Cr6Mn18Co18 and Ni38Fe20Cr10Mn16Co16, exhibited passivity and localized corrosion. The passivity observed in these low chromium MPEAs is likely derived from their relatively high nickel content. Crystallographic pit morphology was observed in most of these MPEAs, suggesting the absence of a salt film on the dissolving pit surface. Such crystallographic pit morphology indicates that the pit growth in most of these MPEAs was under charge-transfer/ohmic control.
The pitting corrosion resistance of 316L stainless steel (316L SS) additively manufactured by selective laser melting (SLM) has been reported to be substantially higher than its commercial ...counterpart due to the elimination of MnS inclusions. Here we report that the pitting corrosion resistance of the SLM-produced 316L SS declines drastically after thermal post-processing above 1000 °C. This unanticipated drastic decline in pitting resistance is explained based on the formation of deleterious MnS inclusions in the SLM-produced 316L SS after high-temperature thermal post-processing. This finding may have wide implications for determining suitable post-processing and industry application conditions for SLM-produced 316L SS.
Type 316L stainless steel manufactured by laser powder bed fusion (LPBF) in conjunction with appropriate post-treatment has been demonstrated to offer superior pitting resistance and a distinct ...pitting mechanism compared to wrought 316L. This work examines the effect of post-processing annealing time, temperature and microstructural changes on the pitting behaviour of LPBF 316L using potentiodynamic and potentiostatic polarisation in 0.6 M NaCl. Preferential pitting at melt pool boundaries was observed, due to heterogeneity of micro-strain or lattice imperfection. High temperature annealing resulted in the transformation of amorphous oxides with associated Cr-depletion, leading to a reduction of Epit and Erp.
•An essentially porosity-lean 316L stainless steel was prepared by LPBF and subjected to cyclic potentiodynamic and potentiostatic polarisation analysis in 0.6 M NaCl.•Preferential pitting at melt pool boundaries was observed, due to heterogeneity of micro-strain or lattice imperfection.•An increased pitting potential was detected in the LFBF 316L after annealing at 800 °C for 2 h despite the presence of sigma phase formation.•Simultaneous formation of MnS precipitates and coarsened oxides was observed after annealing at 1000–1100 °C and the latter predominantly contributed to a reduced pitting potential.
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•Pseudomonas aeruginosa corrosion mechanism can be explained using bioenergetics.•Starved P. aeruginosa biofilm is more corrosive than in full medium.•P. aeruginosa biofilm is grown ...to maturity before starvation starts.•Experimental data support the biocatalytic cathodic nitrate reduction theory.
This work showed that a wild-type Pseudomonas aeruginosa (PAO1) grown as a nitrate reducing bacterium biofilm on C1018 carbon steel was more corrosive under organic carbon source starvation. P. aeruginosa biofilms were pre-grown for 2days to achieve maturity before the culture media were changed to fresh culture media with 100% (as in the standard medium), 10%, and 0% organic carbons for subsequent 7-day incubation. Biofilms with 100%, 10%, and 0% organic carbons caused maximum pit depths of 5.4μm, 10.6μm, and 17.0μm, respectively. Weight loss, linear polarization resistance and electrochemical impedance spectroscopy data corroborated the pitting data.
•Corrosion behavior of additively manufactured (AM) Ti–6Al–4V was examined.•Effect of the adsorption of Br− and Cl− ions on pitting corrosion was investigated.•Competitive adsorption of anions on ...pitting was simulated by Langmuir isotherm.•The relationship between the pitting, the doping densities and α′ phase was established.
Herein, the corrosion behavior of the additively manufactured (AM) Ti–6Al–4V is investigated based on the relation between the pitting potentials and equilibrium adsorption of the Br− and Cl− anions using potentiodynamic polarization curves, Mott–Schottky plots, and the Langmuir isotherm model. The Mott–Schottky plots are measured using the microdroplet cell technique based on the capacitance of the passive films on each dark and bright AM Ti–6Al–4V grain. The pitting potential can be attributed to the doping densities as well as α′ phase distribution and predicted using the equilibrium adsorption coefficient of Br− and Cl−.
•6% Cr steel exhibits a protective passive film with Cr oxide/hydroxide layer.•High pitting corrosion resistance is highlighted for 6% Cr steel.•Compact rust layer is formed for 6% Cr steel after ...natural exposure.
The electrochemical performance of a new 6% Cr steel was investigated intensively by means of a broad variety of electrochemical methods (EIS, CV and CPP) and surface characterization techniques (AFM, XPS, EPMA and ESEM/EDS) in simulated concrete pore solution (SCPS) with chlorides. Improved corrosion resistance of 6% Cr steel in SCPS was established by the protective passive film, the high pitting corrosion resistance as well as the compact rust layer, which may shed light on the design of corrosion-resistant reinforcing steels with enhanced corrosion resistance throughout the service life of reinforced concrete structures.
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•A schematic four-layered structural model of the natural oxide film has been constructed.•A novel concept for the Pilling–Bedworth ratios of chemical compounds is proposed.•Grain ...refinement in the microstructure leads to a shift from pitting corrosion to overall corrosion.•A method to characterise the corrosion rate of dual phase Mg–Li–Ca alloys is proposed.
The influence of the microstructure and the oxide film of the Mg–9.29Li–0.88Ca alloy on its corrosion behaviour was investigated using SEM, EPMA, XPS and corrosion measurements. The results demonstrated that the fine-grained microstructure improved the mechanical and corrosion resistance of the alloy and shifted pitting corrosion to overall corrosion. The oxide film contained a multi-layered structure, with the outer layer being enriched in lithium-bearing compounds; the interior layer predominantly consisting of oxides, hydroxides and carbonates of lithium and magnesium; and the bottom layer containing oxides. The Pilling–Bedworth ratio for chemical compounds was proposed, and the corrosion rates were characterised.
In previous work, a design approach combining computational modeling and empirical knowledge has been reported to establish a more efficient paradigm for developing future corrosion resistant alloys. ...Using this approach, a single-phase non-equimolar high entropy alloy (HEA) was successfully designed and synthesized. In this work, a detailed experimental investigation of the localized corrosion behavior of this alloy is presented. The HEA was found to possess superior intrinsic pitting resistance and exhibit strong passivity, even in 6 M HCl. The ability of this HEA to initiate and propagate a pit has been studied. The pitting resistance was shown to result from the formation of a passive film with exceedingly strong resistance to breakdown and from a high resistance to pit propagation. Pitting was found to be significantly inhibited because of the extremely strong passivity, even in solutions with lower pH and higher chloride concentration than found in a typical local pit environment. The outstanding properties of the HEA validate the approach used for designing corrosion-resistant HEAs.
•Computational designed single phase HEA with superior intrinsic pitting resistance.•Designed HEA exhibits extremely strong passivity even in 6 M HCl.•Passive film breakdown was significantly inhibited on designed HEA.•Pit growth stability on HEA was greatly reduced due to an extremely small idiss,max.
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