Abstract The reactivation of a corrosion pit under the synergetic effect of strain and electro-ch... more Abstract The reactivation of a corrosion pit under the synergetic effect of strain and electro-chemical polarisation has been observed in a type 304L stainless steel using X-ray computed tomography. The pit reactivation process was associated with the formation of a new pit, directly adjacent to a pre-existing pit. Pit growth kinetics were estimated, revealing an increase of the diffusivity parameter ( D eff Δ C ) from 3.0 × 10 −8 mol cm −1 s −1 to 4.5 × 10 −8 mol cm −1 s −1 with the application of strain, indicating higher metal dissolution rates. Applied strain resulted in fractured lacy metal covers, and its effect on pit growth kinetics is discussed.
Abstract Bipolar electrochemistry was applied to determine the full spectrum of anodic-to-cathodi... more Abstract Bipolar electrochemistry was applied to determine the full spectrum of anodic-to-cathodic polarisation behaviour of stainless steel. The potential and current distributions at the sample surface were determined using a segmented array bipolar electrode (BPE). The measured potential shows a quasi-linear gradient along the centre of the BPE, with the current following an exponential Butler–Volmer-type relationship. Bipolar electrochemistry is compared to conventional 3-electrode polarisation testing, allowing determination of the critical pitting potential, general corrosion rates and the cathodic current response. The application of bipolar electrochemistry is demonstrated via measurement of pit growth kinetics in ferritic stainless steel.
Abstract Meso-structural models are presently in common use for analysis of the mechanical behavi... more Abstract Meso-structural models are presently in common use for analysis of the mechanical behaviour, damage evolution and failure of concrete. These are constructed either from XCT images, or in silico, using statistical information about concrete’s meso-scale constituents. As a minimum, such models include mortar and aggregates as separate phases, while more detailed versions consider the interfacial transition zones (ITZ) between mortar and aggregates, and voids. Analyses of given meso-structures vary further by different constitutive modelling of constituents, with past works focusing on parameters’ calibration using experiments with one loading condition - either tension or compression. Using a detailed meso-structure representation, this work proposes a novel combination of constitutive relations, involving concrete damage plasticity (CDP) for mortar and cohesive zone behaviour for ITZ. CDP parameters are calibrated using both compression and tension experiments with mortar samples. ITZ parameters are calibrated by comparing simulated stress–strain curves and failure patterns with data from compression and tension experiments with concrete samples. This process leads to constitutive relations, applicable to both loading conditions, which has not been demonstrated previously, but is essential to extending the modelling approach to complex stress states encountered in real engineering structures. After establishing the realism of the approach, parametric studies are conducted to investigate the effects of friction between loading plate and specimen, the mortar dilation angle, the ITZ cohesive stiffness, critical stresses, fracture energy and mix mode ratio. The results show that mortar plasticity is the dominant energy dissipation mechanism in both compression and tension, and its rate governs the localisation of damage. The effect of ITZ parameters on the tensile behaviour is found to be negligible. Their effect on the compressive behaviour is found to be limited, but sufficient to propose a set of parameters working for both conditions. Importantly, under both loadings the ITZ is found to control failure localisation into a macroscopic crack in combination with mortar plasticity and damage. Predicted stress-stain curves, damage evolution and macro-crack propagation are shown to be in very good agreement with the experimental observations. This justifies the use of the proposed experimental-modelling strategy for developing models for analysis of complex loading conditions.
Corrosion rates of strained grade UNS S32202 (2202) and UNS S32205 (2205) duplex stainless steel ... more Corrosion rates of strained grade UNS S32202 (2202) and UNS S32205 (2205) duplex stainless steel wires have been measured, in situ, using time-lapse X-ray computed tomography. Exposures to chloride-containing (MgCl2) atmospheric environments at 50 °C (12–15 M Cl− and pH ~5) with different mechanical elastic and elastic/plastic loads were carried out over a period of 21 months. The corrosion rates for grade 2202 increased over time, showing selective dissolution with shallow corrosion sites, coalescing along the surface of the wire. Corrosion rates of grade 2205 decreased over time, showing both selective and pitting corrosion with more localised attack, growing preferentially in depth. The nucleation of stress corrosion cracking was observed in both wires.
Abstract The reactivation of a corrosion pit under the synergetic effect of strain and electro-ch... more Abstract The reactivation of a corrosion pit under the synergetic effect of strain and electro-chemical polarisation has been observed in a type 304L stainless steel using X-ray computed tomography. The pit reactivation process was associated with the formation of a new pit, directly adjacent to a pre-existing pit. Pit growth kinetics were estimated, revealing an increase of the diffusivity parameter ( D eff Δ C ) from 3.0 × 10 −8 mol cm −1 s −1 to 4.5 × 10 −8 mol cm −1 s −1 with the application of strain, indicating higher metal dissolution rates. Applied strain resulted in fractured lacy metal covers, and its effect on pit growth kinetics is discussed.
This paper reports on the distribution and precipitation properties of interfaces in two austenit... more This paper reports on the distribution and precipitation properties of interfaces in two austenitic stainless steels as a function of thermomechanical processing. Specimens of type 316 stainless steel were aged at 750° for one week, and the ensuing intergranular precipitation was assessed. Specimens of type 304 stainless steel were processed by a single step of 5% tensile strain followed by annealing at temperatures between 950°C and 1050°C. Selected data sets from both the 316 and 304 specimens were investigated by the new ‘five-parameter’ analysis method, which allows all five parameters of a grain boundary, i.e. both the misorientation and the boundary plane, to be determined. The distributions obtained showed significant differences between the two specimens, which were explained and discussed with reference to the processing routes. Some of the data were compared with a parallel set of experiments where the deformation had been applied by cold rolling. There were differences in...
ABSTRACT The influence of cold roll reduction history on grain boundary network development in an... more ABSTRACT The influence of cold roll reduction history on grain boundary network development in an austenitic stainless steel has been investigated. A dominant effect of the final thermomechanical process cycles on grain boundary character development was observed. The application of low-strain processing cycles with 5% cold reduction was found to increase the fraction of Sigma 3 and Sigma 3-related variants on solution annealing. Two-step processing treatments with final reductions between 15% and 82% showed no significant differences to their single-step processed equivalents. (c) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
SummaryTwo different grain boundary engineering processing routes for type 304 austenitic stainle... more SummaryTwo different grain boundary engineering processing routes for type 304 austenitic stainless steel have been compared. The processing routes involve the application of a small level of strain (5%) through either cold rolling or uni‐axial tensile straining followed by high‐temperature annealing. Electron backscatter diffraction and orientation mapping have been used to measure the proportions of Σ3n boundary types (in coincidence site lattice notation) and degree of random boundary break‐up, in order to gain a measure of the success of the two types of grain boundary engineering treatments. The distribution of grain boundary plane crystallography has also been measured and analyzed in detail using the five‐parameter stereological method. There were significant differences between the grain boundary population profiles depending on the type of deformation applied.
Abstract The reactivation of a corrosion pit under the synergetic effect of strain and electro-ch... more Abstract The reactivation of a corrosion pit under the synergetic effect of strain and electro-chemical polarisation has been observed in a type 304L stainless steel using X-ray computed tomography. The pit reactivation process was associated with the formation of a new pit, directly adjacent to a pre-existing pit. Pit growth kinetics were estimated, revealing an increase of the diffusivity parameter ( D eff Δ C ) from 3.0 × 10 −8 mol cm −1 s −1 to 4.5 × 10 −8 mol cm −1 s −1 with the application of strain, indicating higher metal dissolution rates. Applied strain resulted in fractured lacy metal covers, and its effect on pit growth kinetics is discussed.
Abstract Bipolar electrochemistry was applied to determine the full spectrum of anodic-to-cathodi... more Abstract Bipolar electrochemistry was applied to determine the full spectrum of anodic-to-cathodic polarisation behaviour of stainless steel. The potential and current distributions at the sample surface were determined using a segmented array bipolar electrode (BPE). The measured potential shows a quasi-linear gradient along the centre of the BPE, with the current following an exponential Butler–Volmer-type relationship. Bipolar electrochemistry is compared to conventional 3-electrode polarisation testing, allowing determination of the critical pitting potential, general corrosion rates and the cathodic current response. The application of bipolar electrochemistry is demonstrated via measurement of pit growth kinetics in ferritic stainless steel.
Abstract Meso-structural models are presently in common use for analysis of the mechanical behavi... more Abstract Meso-structural models are presently in common use for analysis of the mechanical behaviour, damage evolution and failure of concrete. These are constructed either from XCT images, or in silico, using statistical information about concrete’s meso-scale constituents. As a minimum, such models include mortar and aggregates as separate phases, while more detailed versions consider the interfacial transition zones (ITZ) between mortar and aggregates, and voids. Analyses of given meso-structures vary further by different constitutive modelling of constituents, with past works focusing on parameters’ calibration using experiments with one loading condition - either tension or compression. Using a detailed meso-structure representation, this work proposes a novel combination of constitutive relations, involving concrete damage plasticity (CDP) for mortar and cohesive zone behaviour for ITZ. CDP parameters are calibrated using both compression and tension experiments with mortar samples. ITZ parameters are calibrated by comparing simulated stress–strain curves and failure patterns with data from compression and tension experiments with concrete samples. This process leads to constitutive relations, applicable to both loading conditions, which has not been demonstrated previously, but is essential to extending the modelling approach to complex stress states encountered in real engineering structures. After establishing the realism of the approach, parametric studies are conducted to investigate the effects of friction between loading plate and specimen, the mortar dilation angle, the ITZ cohesive stiffness, critical stresses, fracture energy and mix mode ratio. The results show that mortar plasticity is the dominant energy dissipation mechanism in both compression and tension, and its rate governs the localisation of damage. The effect of ITZ parameters on the tensile behaviour is found to be negligible. Their effect on the compressive behaviour is found to be limited, but sufficient to propose a set of parameters working for both conditions. Importantly, under both loadings the ITZ is found to control failure localisation into a macroscopic crack in combination with mortar plasticity and damage. Predicted stress-stain curves, damage evolution and macro-crack propagation are shown to be in very good agreement with the experimental observations. This justifies the use of the proposed experimental-modelling strategy for developing models for analysis of complex loading conditions.
Corrosion rates of strained grade UNS S32202 (2202) and UNS S32205 (2205) duplex stainless steel ... more Corrosion rates of strained grade UNS S32202 (2202) and UNS S32205 (2205) duplex stainless steel wires have been measured, in situ, using time-lapse X-ray computed tomography. Exposures to chloride-containing (MgCl2) atmospheric environments at 50 °C (12–15 M Cl− and pH ~5) with different mechanical elastic and elastic/plastic loads were carried out over a period of 21 months. The corrosion rates for grade 2202 increased over time, showing selective dissolution with shallow corrosion sites, coalescing along the surface of the wire. Corrosion rates of grade 2205 decreased over time, showing both selective and pitting corrosion with more localised attack, growing preferentially in depth. The nucleation of stress corrosion cracking was observed in both wires.
Abstract The reactivation of a corrosion pit under the synergetic effect of strain and electro-ch... more Abstract The reactivation of a corrosion pit under the synergetic effect of strain and electro-chemical polarisation has been observed in a type 304L stainless steel using X-ray computed tomography. The pit reactivation process was associated with the formation of a new pit, directly adjacent to a pre-existing pit. Pit growth kinetics were estimated, revealing an increase of the diffusivity parameter ( D eff Δ C ) from 3.0 × 10 −8 mol cm −1 s −1 to 4.5 × 10 −8 mol cm −1 s −1 with the application of strain, indicating higher metal dissolution rates. Applied strain resulted in fractured lacy metal covers, and its effect on pit growth kinetics is discussed.
This paper reports on the distribution and precipitation properties of interfaces in two austenit... more This paper reports on the distribution and precipitation properties of interfaces in two austenitic stainless steels as a function of thermomechanical processing. Specimens of type 316 stainless steel were aged at 750° for one week, and the ensuing intergranular precipitation was assessed. Specimens of type 304 stainless steel were processed by a single step of 5% tensile strain followed by annealing at temperatures between 950°C and 1050°C. Selected data sets from both the 316 and 304 specimens were investigated by the new ‘five-parameter’ analysis method, which allows all five parameters of a grain boundary, i.e. both the misorientation and the boundary plane, to be determined. The distributions obtained showed significant differences between the two specimens, which were explained and discussed with reference to the processing routes. Some of the data were compared with a parallel set of experiments where the deformation had been applied by cold rolling. There were differences in...
ABSTRACT The influence of cold roll reduction history on grain boundary network development in an... more ABSTRACT The influence of cold roll reduction history on grain boundary network development in an austenitic stainless steel has been investigated. A dominant effect of the final thermomechanical process cycles on grain boundary character development was observed. The application of low-strain processing cycles with 5% cold reduction was found to increase the fraction of Sigma 3 and Sigma 3-related variants on solution annealing. Two-step processing treatments with final reductions between 15% and 82% showed no significant differences to their single-step processed equivalents. (c) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
SummaryTwo different grain boundary engineering processing routes for type 304 austenitic stainle... more SummaryTwo different grain boundary engineering processing routes for type 304 austenitic stainless steel have been compared. The processing routes involve the application of a small level of strain (5%) through either cold rolling or uni‐axial tensile straining followed by high‐temperature annealing. Electron backscatter diffraction and orientation mapping have been used to measure the proportions of Σ3n boundary types (in coincidence site lattice notation) and degree of random boundary break‐up, in order to gain a measure of the success of the two types of grain boundary engineering treatments. The distribution of grain boundary plane crystallography has also been measured and analyzed in detail using the five‐parameter stereological method. There were significant differences between the grain boundary population profiles depending on the type of deformation applied.
Intergranular stress corrosion cracking (SCC) of austenitic stainless steel components is a life-... more Intergranular stress corrosion cracking (SCC) of austenitic stainless steel components is a life-limiting factor in nuclear power plant, in which failure of structural components presents a substantial hazard to both safety and economic performance.
This paper reports an on-going research programme into the mechanisms of intergranular stress corrosion cracking in austenitic stainless steels in simulated light water environments. These make use of new analytical and modelling techniques to develop an improved mechanistic understanding of the influence of materials, environment and stress on SCC. The work aims to establish new approaches for the engineering of microstructures and surfaces to develop stainless steels with improved SCC resistance.
17th International Corrosion Congress Corrosion Control in the Service of Society
Electron Backscatter Diffraction (EBSD) and Image Analysis (IA) techniques have been coupled with... more Electron Backscatter Diffraction (EBSD) and Image Analysis (IA) techniques have been coupled with Double Loop-Electrochemical Potentiokinetic Reactivation (DL-EPR) testing to characterize the development of sensitized grain boundary clusters in Type 304 stainless steel. DL-EPR testing revealed differences in the sensitization response of thermo-mechanically processed microstructures, despite similar grain size and grain boundary character distributions (GBCD). The same sensitization treatment produced different distributions of sensitized grain boundary clusters, and susceptible boundary clusters percolated through all microstructures after sensitization treatments of 4 hrs at 650°C. Assessment of the connectivity of Σ3n (1≤n≤3) grain boundaries in EBSD maps showed a trend to longer clusters with increasing Σ3n (1≤n≤3) fractions. A comparison to DL-EPR data showed the attacked grain boundary networks were generally in excess of 80% of the potentially susceptible grain boundary fraction.
This paper reports on the distribution and precipitation properties of interfaces in two austenit... more This paper reports on the distribution and precipitation properties of interfaces in two austenitic stainless steels as a function of thermomechanical processing. Specimens of type 316 stainless steel were aged at 750° for one week, and the ensuing intergranular precipitation was assessed. Specimens of type 304 stainless steel were processed by a single step of 5% tensile strain followed by annealing at temperatures between 950°C and 1050°C. Selected data sets from both the 316 and 304 specimens were investigated by the new ‘five-parameter’ analysis method, which allows all five parameters of a grain boundary, i.e. both the misorientation and the boundary plane, to be determined. The distributions obtained showed significant differences between the two specimens, which were explained and discussed with reference to the processing routes. Some of the data were compared with a parallel set of experiments where the deformation had been applied by cold rolling. There were differences in the two series of results. After processing which included rolling deformation, the Σ3 boundaries tended to break up the random boundary network, whereas after processing by tensile deformation the grain boundary network had been affected in other ways. The consequences of these findings for grain boundary engineering are briefly discussed.
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Papers by Dirk Engelberg
This paper reports an on-going research programme into the mechanisms of intergranular stress corrosion cracking in austenitic stainless steels in simulated light water environments. These make use of new analytical and modelling techniques to develop an improved mechanistic understanding of the influence of materials, environment and stress on SCC. The work aims to establish new approaches for the engineering of microstructures and surfaces to develop stainless steels with improved SCC resistance.