Intergranular Stress Corrosion Cracking Propagation Research Articles

Study of the relationship between intergranular stress corrosion cracking and grain boundary characteristics in brass

The purpose of this study is to investigate the correlation between intergranular stress corrosion cracking (IGSCC) and grain boundary characteristics in brass. The Volta potential and nature of the grain boundaries in H62 brass were studied by scanning Kelvin probe force microscopy and Electron Backscattered Diffraction, respectively. The α/β phase boundaries and random grain boundaries with low work functions can act as anodic areas to promote IGSCC propagation. Moreover, due to a combination of the inherent characteristics and high work function of Σ3 annealing twin boundaries (ATBs), IGSCC is successfully halted at a triple junction containing Σ3 ATB.

Simulating Intergranular Stress Corrosion Cracking in AZ31 Using Three-Dimensional Cohesive Elements for Grain Structure

In this study, a grain boundary model with three-dimensional (3D) cohesive elements for analyzing the intergranular stress corrosion cracking (IGSCC) on the crystal level in polycrystalline materials is presented. The objectives are to characterize the grain boundary microstructure and the fracture mechanism of IGSCC in AZ31 Mg alloy. In order to investigate the development of the microcrack and its effects on macrocrack evolution, a novel model of IGSCC propagation has been developed, in which the 3D Voronoi tessellations geometry is employed to model polycrystalline grain structures. And the 3D cohesive elements with zero constitutive thickness are directly inserted on the faces of two adjacent grains. The effect of the embrittlement due to the presence of hydrogen has also been included in the cohesive model. To validate the model, an IGSCC process of AZ31 Mg alloy in NaCl solution has been simulated, with the influence of hydrogen concentration being taken into account. It is found that damage develops at the triple lines between the grains and the combinations of grains can lead to high stresses at the grains boundary, especially those that are normal to the direction of the applied strain. In this paper, the effects of damage due to hydrogen and the grain sizes in microstructure are considered. The simulation results have a good consistency with the experimental phenomenon.

Intergranular stress corrosion crack propagation in hot-rolled AZ31 Mg alloy sheet

The susceptibility to stress corrosion cracking (SCC) of hot-rolled AZ31 Mg alloy sheets with different levels of deformation were evaluated by constant extension rate tensile (CERT) testing in distilled water. The normalised macroscopic SCC susceptibilities of the materials, characterised in terms of the normalised UTS and elongation-to-failure, were relatively consistent; however, the predominant mode of SCC propagation was strongly dependent on the microstructure. For all materials, cracks were initiated by localised film rupture and dissolution. Crack propagation through fine-grained, recrystallised regions was intergranular, whereas crack propagation through the larger, original grains was transgranular and tended to follow {101¯2} twin boundaries. In both cases, the crack propagation mechanism was a form of hydrogen embrittlement.

Use of a dislocation-based boundary element model to extract crack growth rates from depth distributions of intergranular stress corrosion cracks

A dislocation-based boundary element model was used to simulate intergranular stress corrosion crack propagation in virtual microstructures. A Monte Carlo approach was used in which the propagation of approximately 100 cracks was calculated for different Voronoi generated microstructures. At every simulation step the model gave the position of the crack tip together with stress intensity factors KI and KII. Using a simple power-law-type crack growth rate da/dt=DpKmp, the depth of each particular crack can be calculated knowing the time the samples were exposed to the stress and corrosive environment. Existing experimental data giving crack depth distributions for Alloy 600, and XM-19 and 304 stainless steel are investigated and the best-fit crack growth law established. Alloy 600 in a light water reactor environment and XM-19 in high-temperature water both lead to mp=3. While for 304 stainless steel in the more aggressive K2S4O6/H2SO4 (pH 2) an exponent mp=0.8 was found.

Analysis of acoustic emission signals generated from SCC propagation

This paper presents a comparison between the acoustic emission (AE) signals generated by the transgranular stress corrosion cracking (TGSCC) of Ag–10Au (at.%) single crystals and those originated by the intergranular stress corrosion cracking (IGSCC) of a polycrystalline silver–gold alloy under the same experimental conditions. No significant difference is found between the mean amplitude and rise-time of the AE signals registered during the propagation of TGSCC and those measured for IGSCC propagation. Results also show that the AE signals generated by either TGSCC or IGSCC propagation in three different alloys such as AISI 304 SS, α-brass and Ag–Au alloys show similar AE parameters and similar amplitude distribution.

A novel microstructure – Grain boundary character based integrated modeling approach of intergranular stress corrosion crack propagation in polycrystalline materials

A novel integrated modeling approach, using Markov Chain theory, Voronoi algorithm for microstructure construction, and Monte Carlo simulations, has been presented in order to predict the intergranular stress corrosion cracking (IGSCC) behaviour in polycrystalline materials. The model takes both the physical microstructural features, such as the grain size distribution and grain shape, as well as the grain boundary character distribution (GBCD) and their orientation with respect to the external stress axis into account. Besides, several characteristic features of IGSCC such as, crack-branching and coalescence, multiple crack-nucleation sites, and crack-turn have been incorporated in the model. The predicted crack-propagation behaviour is in reasonable agreement with the electron back-scattered diffraction (EBSD) based experimentally determined relationship between the GBCD and 2D crack-percolation frequency of API 5L X65 pipeline steel.

A Markov Chain–Monte Carlo model for intergranular stress corrosion crack propagation in polycrystalline materials

A model for intergranular stress corrosion crack propagation in polycrystalline materials has been proposed which overcomes several limitations of the currently available model in the literature for this purpose. Markov Chain theory and Monte Carlo simulations have been combined to predict the maximum crack lengths for different grain boundary character distributions. The effects of grain boundary orientation with respect to the stress axis, frequent and sporadic crack-branching, crack-turn, multiple crack nucleation sites, grain shape, and variable vulnerabilities of the same type of grain boundaries along the depth of the materials on the final crack-length have been investigated. It has been found that the percolation threshold reported in the literature for honeycomb structure is not valid when the boundary inclination with respect to the stress direction is considered. Incorporation of realistic type crack-turn suggests that, although crack-turning increases the crack length, especially, when the fraction of vulnerable boundaries is relatively high, it is, by no means, as significant as crack-branching or multiple crack initiations in a given microstructure. It has also been observed that infrequent crack-branching, a common occurrence in intergranular stress corrosion cracking of polycrystalline materials, can decrease the crack length to a great extent, indicating that assuming a branching probability of 1 can overestimate the possible intergranular crack length for a given grain boundary character distribution. On the other hand, increased vulnerabilities of different types of grain boundaries with the depth of the material can lead to percolation, which is otherwise unpredictable.

AE response of type 304 stainless steel during stress corrosion crack propagation

Acoustic emission (AE) signals generated by transgranular stress corrosion cracking (TGSCC) and intergranular stress corrosion cracking (IGSCC) have been compared by means of slow strain rate tensile tests (SSRT) performed using both solubilised and sensitised type AISI 304 stainless steel in a 1 M NaCl + 1 M HCl solution. Results show that the AE activity during the propagation of TGSCC is much higher than the AE activity during the IGSCC propagation. However, no significant difference was found between the mean amplitude and rise-time of the AE signals registered during the propagation of TGSCC and those measured for IGSCC propagation.

The correlation of IGSCC propagation with the power plant transient history

The purpose of this study was to find out the possible correlation between the crack propagation and the shut-downs and start-ups of the nuclear power plant. These transients can promote intergranular stress corrosion cracking (IGSCC) through stress variations and changes in water chemistry. This work was conducted by studying cracks found from the AISI 304 shut-down cooling and clean-up pipeline. The appearance of observed cracking paths were compared to the transient history of the plant and the crack growth rates were evaluated based on these results. Principles of probabilistic modeling of the IGSCC growth in operational conditions will also be presented and simple examples of possible applications of the model related to existing data are given.

高温純水中における鋭敏化ステンレス鋼の粒界応力腐食割れ成長挙動

高温純水中における鋭敏化ステンレス鋼の粒界応力腐食割れ成長挙動