Cavity Growth Research Articles

Effect of Ce on creep damage behavior of 316LN austenitic stainless steel at 700 °C

The effect of rare earth element Ce on creep damage behavior of 316LN austenitic stainless steel (316LN) at 700 °C was systematically investigated under stress ranging from 125 MPa to 200 MPa. The results show that the addition of 0.032 wt% Ce remarkably improves the rupture life of 316LN steel under various stress. Ce addition in 316LN steel decreases the nucleation stress, stabilizes stress concentrations at particles, and notably raises the cavity nucleation rate. Moreover, Ce addition suppresses cavity growth during creep, thus the cavity growth rate significantly decreases and the creep rupture ductility increases under high stress over 175 MPa. However, the anomalous growth rate was engendered in some cavities by Ce addition in 316LN steel under low stress below 150 MPa. Consequently, Ce addition in 316LN steel reduces the creep rupture ductility and changes the rupture mode from trans-granular dimple fracture under high stress to mixed fracture under low stress.

Pitting corrosion behavior and mechanism of 316L stainless steel induced by marine fungal extracellular polymeric substances

In this study, effect of extracellular polymeric substances (EPS) secreted by fungus Aspergillus terreus on the pitting corrosion of 316L stainless steels (SS) was deeply investigated by electrochemical measurements and surface analysis. Results demonstrated that adsorption of EPS can change surface wettability of 316L SS leading to a much more hydrophilic steel–water interface. EPS not only accelerates uniform corrosion but enhances pitting corrosion of 316L SS. EPS can promote the formation of metastable pitting corrosion and the subsequent growth of corrosion pits. The density of corrosion pits (>2 µm) reach (5.6 ± 0.5)× 103 pits/cm2 when EPS is 400 mg/L.

Oral Manifestation of Viral-Induced Erythema Multiforme Major: A Rare Presentation.

Erythema multiforme is an acute inflammatory mucocutaneous disease manifested as macules, vesicles, bullae, erosion, and papular lesions. In the present case, a 55-year-old female patient reported painful growth in the oral cavity and difficulty in mastication. The patient gave a history of prodromal symptoms before the onset of lesions On intra-oral examination, elevated plaque-like lesions were present bilaterally on lateral borders of the tongue and buccal mucosa near the retromolar region. Extraoral examination revealed concentric erythematous target (or) bull's eye lesions in palms, forearm, and foot. Based on history, clinical examination, and laboratory investigations, recurrent herpes-associated erythema multiforme was diagnosed. We report a rare clinical presentation of recurrent herpes-associated erythema multiforme manifesting as an extensive plaque-like lesion intra-orally.

Data-driven model to predict burst pressure in the presence of interacting corrosion pits

This paper presents a data-driven approach to predict the pipelines’ corrosion-induced Burst failure. In this approach, different aspects of pit growth progression and spatial distribution of pits are simulated. The proposed approach takes advantage of population characteristics to model these aspects of the degradation paths for each pipe section down to the size of single joints. The insights obtained from simulations are used to project the degradation of each pipe section. Understanding corrosion behavior and field data are used to model the corrosion-related parameters such as corrosion pit dimensions, probability and time of initiation, and location. The failure is modeled using the probabilistic simulation considering degradation rate, interactions among pits, and material properties as stochastic variables. The proposed approach and included models are tested using multiple real-life inline inspection datasets. Validation of predicted properties shows prediction errors ranging from 3%–10% depending on the three remaining strength calculation approaches. This work aimed to serve as an important tool for risk-based maintenance prioritization, inspection interval assessment, and the fitness of service assessment of pipelines.

A rapid corrosion screening technique for grade 2707 hyper‐duplex stainless steel at ambient temperature

AbstractThe pitting corrosion behaviour of 27%Cr–7%Ni (2707) hyper‐duplex stainless steel (HDSS) at ambient temperature has been assessed using a novel bipolar electrochemistry test set‐up. Application of this technique generates a linear potential gradient at the surface of the HDSS 2707 test piece, which allows assessment of the pitting corrosion behaviour at ambient temperature. Pit nucleation and associated growth kinetics can be obtained and characterised. To assess pitting corrosion in high‐alloyed HDSS, the normal bipolar test method had to be modified by superimposing an auxiliary potential. This new test set‐up was demonstrated by characterising the nucleation of pits and associated pit growth kinetics. The latter occurred either at austenite/ferrite interphase or inside ferrite phase, with pit growth within the ferrite phase in the HCl environment.

A Cavity-Based Micromechanical Model for the Shear-Band Failure in Metallic Glasses Under Arbitrary Stress States

Abstract Deformation and fracture of metallic glasses are often modeled by stress-based criteria which often incorporate some sorts of pressure dependence. However, detailed mechanisms that are responsible for the shear-band formation and the entire damage initiation and evolution process are complex and the origin of such a pressure dependence is obscure. Here, we argue that the shear-band formation results from the constitutive instability, so that the shear-band angle and arrangements can be easily related to the macroscopic constitutive parameters such as internal friction and dilatancy factor. This is one reason for the observed tension-compression asymmetry in metallic glasses. The free volume coalescence leads to precipitous formation of voids or cavities inside the shear bands, and the intrinsic “ductility” is therefore governed by the growth of these cavities. Based on a generalized Stokes–Hookean analogy, we can derive the critical shear-band failure strain with respect to the applied stress triaxiality, in which the cavity evolution scenarios are sharply different between tension-controlled and shear/compression-dominated conditions. This is another possible reason for the tension-compression asymmetry. It is noted that diffusive-controlled cavity growth could also be the rate-determining process, as suggested by the recent measurements of shear-band diffusivity and viscosity that turn out to satisfy the Stokes–Einstein relationship. This constitutes the third possible reason for the tension-compression asymmetry.

Pit growth kinetics in aluminum: effects of salt loading and relative humidity

The growth kinetics of localized corrosion, e.g. pits, in corrosive environments often controls the service life of metallic components. Yet, our understanding of these kinetics is largely based on coupon-level, e.g. mass-loss, studies which provide limited insights into the evolution of individual damage events. It is critical to relate observed cumulative loss trends, such as links between changing humidity and mass loss rates, to the growth kinetics of individual pits. Towards this goal, we leverage in-situ X-ray computed tomography to measure the growth rates of over sixty pits in aluminum in four different humid, chloride environments over ≈3 days of exposure. Pit growth rates and final volumes increased with increasing droplet volume, which was observed to increase with increasing humidity and salt loading. Two factors, droplet spreading and oxide jacking, dramatically increased pit growth rates and final volumes.

Improving the long-term corrosion resistance of HVOF sprayed WC-Cr3C2-Ni coating by vacuum sealing with silicone resin

The properties of thermal sprayed WC based cermet coatings are limited by their structural defects, especially corrosion resistance. This article studied the influence of vacuum sealing with silicone resin on the long-term corrosion resistance of HVOF sprayed WC-Cr3C2-Ni coating in 3.5 wt.% NaCl solution. The surface morphologies of the unsealed and sealed coatings show the high compatibility between sealant and WC-Cr3C2-Ni coating. Benefiting from the block of sealant in defects, the sealed coating presents lower corrosion current density (5.843 × 10−8 A cm−2) after long-term corrosion than the unsealed coating (1.776 × 10−7 A cm−2). Owing to the vacuum treatment, sealant adequately penetrates and remains inside the WC-Cr3C2-Ni coating, and inhibits the growth of corrosion pits on the sealed coating surface. The vacuum sealing with silicone resin effectively hinders the diffusion of corrosion solution, and provides practicable strategy to improve the corrosion resistance of the coatings.

Stress corrosion cracking under extreme near-neutral GCC conditions, parametric and comparative study using phase field modeling

Stress Corrosion Cracking (SCC) is a failure mechanism that occurs when certain materials are subjected to both external or residual stresses and corrosion. This combined effect leads to the development of cracks in the susceptible materials. Submerged steel pipelines in the petroleum sector are built of low-alloy steels having a ferrite-cementite composition, including API 5L X70. Such materials are sensitive to SCC damage in aqueous systems. The film rupture dissolution repassivation (FRDR) process is used in this study to evaluate the cracks and pits growth in oil and gas pipelines in the Gulf area under diverse SCC environmental conditions. The SCC crack propagation and pit growth under near-neutral environmental conditions were analyzed using phase field modelling. X70 steel under NS4 the solution was used for the analysis to represent the anodic dissolution film rupture mechanism. A parametric study was done to study the impact of different electrochemistry and phase field parameters on crack growth behaviour. The study assess the susceptibility to SCC caused by an pit by employing diverse settings to evaluate the impact of corrosion parameters and the interaction among the FRDR mechanism. The corrosion rates are influenced by the interface kinetics coefficient (L), which exhibits an accelerated effect as L increases. This transition from fracture-controlled to dissolution-controlled SCC growth occurs until the system reaches the diffusion limit, beyond which further increases in L do not significantly impact corrosion rates. Moreover, higher values of the kinetic coefficient (k) advance the creation of SCC cracks at the crack front, resulting from corrosion originating from pitting at the crack mouth. This process leads to the refinement of the pit and its transformation into a crack. A comparison analysis was utilized to validate our simulation under a near-neutral NS4 solution for X70 steel by correlating the findings with other numerical methods for crack growth utilizing the same material and environmental parameters. The results show decent agreement with the comparative study.

Application of bipolar electrochemistry to assess the corrosion resistance of solution annealed lean duplex stainless steel

The corrosion performance of type 2101 lean duplex stainless steel (LDSS) after different solution annealing heat treatments is investigated. The austenite to ferrite phase ratios and morphologies are correlated to their localised corrosion responses, with the application of bipolar electrochemistry providing access to pit nucleation and growth kinetics. The propagation of pitting corrosion via selective dissolution of the ferrite phase is observed, pointing towards a direct effect of ferrite morphology on pit shape. The corrosion behaviour of solution heat treatments are compared and ranked, providing information for improving and optimising the corrosion resistance of LDSS 2101 microstructures.

Keterkaitan antara Halitosis dengan Bakteri Penyebab Periodontitis

Halitosis, often known as foul breath, refers to an unpleasant odor that emanates from the mouth cavity when inhaling or talking. Halitosis can have a negative impact on a person's quality of life, including symptoms of depression or anxiety, low self-esteem, embarrassment, prejudice, and social isolation. Bad breath can be caused by both intra oral and extra oral factors. Bacterial growth in the oral cavity is excellent for the production of volatile sulfur compounds (VSC). The posterior dorsum of the tongue, gingival sulcus, periodontal pockets, and gingival embrasures are all places where bacterias can accumulate. Fusobacterium nucleatum, Prevotella intermedia, Porphyromonas gingivalis, and Treponema dentiocola are known to actively produce VSC through interactions with specific substrates such as cysteine, methionine, tryptophan, arginine, and lysine to produce hydrogen sulfide (H2S) and methylmercaptan (CH3SCH3). However, the presence of VSC does not indicate the presence of periodontitis, as any space in the oral cavity that can cause the retention of bacteria/biofilms can become a site for bacterial decomposition, thereby facilitating the growth of VSC. Tongue cleansing is proven to help reduce the formation of VSC.

Investigation of transient sheet/cloud cavitating flow dynamics from multiscale perspective

Sheet/cloud cavitation usually leads to a wide range of length scales in both turbulence and phase distribution from microbubbles to cavity advection. In the present work, the Eulerian–Lagrangian multiscale cavitation model with two-way coupling is utilized to simulate the cavitating flow around a (National Advisory Committee for Aeronautics) NACA66 hydrofoil at an incidence angle of 8° and a cavitation number of σ = 1.4. The model can simultaneously capture the large-scale cavities and the microscale bubbles. The cavitating flow features are in good agreement with the experimental observations containing not only the periodical formation, growth, detachment, and advection of large-scale cavities, but also thousands of microbubbles around the large-scale cavities. The results show that the overall evolution frequency in the flow is about 45 Hz. Meanwhile, the dynamic mode decomposition method is utilized to identify the large-scale coherent spatial and temporal features of the sheet/cloud cavitating flow, which indicates that complex vortices in various scales dominate the evolution of cavities in the corresponding scale, and the evolution frequency of large-scale vapor structure decreases with increasing the length scale of cavities. Under the effect of turbulence, the large-scale cavities break into microbubbles, causing the size and number of discrete bubbles to increase rapidly in the re-entrant jet and cloud shedding regions. Additionally, the bubble-size spectrum of the time-averaged distribution of a period in sheet/cloud cavitating flow has two size regimes. For larger bubbles, the bubble density is proportional to the bubble radius to the power of −10/3. The bubble size spectrum of smaller microbubbles exhibits a −4/3 power-law scaling.

Role of Copper on Repassivation of Stainless Steel Pits

The effect of copper on the repassivation of pits in stainless steels was examined through potentiodynamic polarization of one-dimensional (1D) pits at two different downward scan rates for 17–4 PH stainless steel. Post-mortem characterization of tested 1D pits revealed that copper enriches on the pit surface, which most likely occurs through reduction of CuCl3 2− inside the pit during the downward potential scan. 1D diffusion analysis revealed significant amounts of copper replating can occur before the attainment of critical pit chemistry for repassivation when scanning at a high rate, which complicates repassivation potential (E rp) measurements. Copper replating may lead to higher value of measured E rp by, (i) reducing the measured net anodic current density, (ii) blocking the dissolution of stainless steel underneath the copper deposits, (iii) enhancing local hydrogen evolution kinetics to raise the pH of the pit bottom. The relative strength of the copper replating effect is controlled by scan rate or more generally, pit growth conditions and local pit chemistry. Implications of the copper replating effect on measuring a lower-bound value of repassivation potentials are discussed in light of existing repassivation potential measurement techniques. The pit growth conditions that could lead to copper replating in real pits are discussed.

Interaction of Stacking Faults with point/extended defects in Fe-He irradiated 6H-SiC

The study explored the microstructure evolution of 6H-SiC that underwent sequential iron and helium ion irradiation with energies of 2.5 MeV and 500 keV, respectively, at room temperature, followed by annealing at 1500°C for two hours. Following irradiation, the entire damaged layer underwent amorphization. However, during subsequent annealing, epitaxial recrystallization took place, resulting in the formation of defected polycrystalline 6H-SiC characterized by the presence of Fe-rich clusters, cavities, and stacking faults. Fe-rich cavities were found to predominantly form at the edges of the stacking faults, as revealed by XTEM. The interaction of microstructural defects is further investigated via first-principles calculations. The periphery of the stacking faults has been identified as the primary location for the emergence of vacancy clusters, serving as favorable sites for the accumulation of point defects, including Fe atoms. This behavior can be attributed to the combined effects of mechanical and electronic energy relaxation mechanisms. Mechanically, the presence of stacking faults allows for the release of elastic energy that had been stored at the boundary. Electronically, the energy relaxation arises from the saturation of C- and Si-dangling bonds. Both of these processes contribute to the observed behavior, highlighting the intricate interplay between mechanical and electronic factors in the system. The low point defect migration energy barriers in the vicinity of the stacking faults promise high recombination, which can limit cavity growth and enhance radiation resistance. The study not only offers valuable insights into the mechanism of cavity/stacking faults interaction, contributing to a better understanding of radiation damage in 6H-SiC but also demonstrates that 6H-SiC material containing stacking faults could serve as a viable alternative to 3C-SiC for nuclear application.

Cavity growth behavior and fracture mechanism of 9.5Cr-1.5MoCoVNbNB heat-resistant steel during long-term tensile rupture at 620 °C

Heat-resistant materials appropriate for use in long-term ultra-supercritical coal-fired power generation are increasingly important. To this end, we tested a series of 9.5Cr-1.5MoCoVNbNB heat-resistant steel samples at 620 °C under applied stresses of 155–225 MPa until rupture. The microstructural characteristics, cavity growth behavior, and fracture mechanism of the tensile rupture samples were investigated. Stress promotes the motion of dislocations density, subgrain formation, and cavity nucleation. The cavities continuously grow and coalesce, but the growth rates and coalescence rates may be lower under low stress values than those under high applied stress. A detailed assessment revealed two types of inclusions, BN and Al2O3, in the tested steel. The cavities around the BN inclusions tend to deform with stress, while those around the Al2O3 inclusions tend to promote nucleation of cracks. 9.5Cr-1.5MoCoVNbNB heat-resistant steel fracture is mainly induced by cavity coalescence around inclusions.

Yield surface for void growth and coalescence of porous anisotropic materials under axisymmetric loading

Ductile fracture in metallic alloys occurs by growth and coalescence of cavities. Growth, also referred to as homogeneous yielding, refers to rather diffuse plasticity around cavities, while coalescence, also termed as inhomogenous yielding, corresponds to the localization of plasticity along some planes or directions. Coalescence can develop in various patterns; three coalescence modes have been observed experimentally: internal necking, coalescence in columns and void sheeting. Plastic anisotropy of the material is known to have a significant effect on both homogeneous and inhomogeneous yielding. Therefore, in the present study, yield criteria accounting for the transition from homogeneous yielding to inhomogeneous yielding modes in anisotropic porous materials are obtained using kinematic limit analysis on a cylindrical unit-cell with a coaxial cylindrical cavity. Two types of plastic anisotropy are considered: Hill (1948) plasticity and crystal plasticity. The proposed analytical yield criteria are compared to numerical limit analysis computations and are found to qualitatively agree with simulations. In particular, plastic anisotropy, void shape effects and their coupling are well captured, especially regarding yield stresses and deformation modes. Finally, an homogenized model for Hill porous materials is obtained by supplementing evolution laws for microstructural parameters (void aspect ratio and ligament size ratios) derived from sequential limit analysis. Proposed evolution laws are then discussed in the light of numerical results and experimental evidence.

Ultra-Low Cycle Fatigue Life Prediction Model—A Review

This article is a review of models for predicting ultra-low cycle fatigue life. In the article, the life prediction models are divided into three types: (1) microscopic ductile fracture models based on cavity growth and cavity merger; (2) fracture models based on porous plasticity; and (3) ductile fracture models based on continuum damage mechanics. Furthermore, the article provides a critical assessment of the current state of research on ultra-low cycle fatigue life prediction models, highlighting the limitations and challenges faced by each model type. Ultimately, this review aims to provide a comprehensive overview of the different models available for predicting ultra-low cycle fatigue life and to guide future research in this important area of materials science and engineering.

Numerical study of impact phenomena due to cavitation bubble collapse on metals and polymers

Metals and polymers are the materials most frequently used in hydromachinery components that are prone to cavitation damage. This study examined the damage mechanism of metals (titanium, SUS304, Al2024, and magnesium) and polymers (nylon, Teflon, Adiprene, epoxy, and polyethylene) due to cavitation bubble collapse by utilizing a coupled fluid–solid hydrocodes solver. An air bubble was positioned adjacent to solid material within a long and narrow water-filled channel. A planar shockwave was utilized to create instability within the air bubble, causing a nonspherical collapse that is often observed in cavitation bubbles. By analyzing the wave propagation behavior of bubble collapse impact load (BCIL) acting on the surface, it was revealed that in metals, the impact load is primarily transmitted as elastic waves of compression and shear. Hence, the cavitation damage on metals can be defined by BCIL and acoustic impedance. On the other hand, the BCIL on polymers generates an excessive plastic deformation, so called cavitation pit. An image analysis on cavitation pit growth demonstrated a strong correlation between the pit’s volume and depth with the polymer’s yield strength.

Creep Deformation Behavior, Microstructure Evolution, and Damage Mechanism of Super304H ODS Steel

In this paper, the creep deformation behavior, microstructure evolution, and damage mechanism of Super304H oxide dispersion strengthened (ODS) steel have been systematically investigated at 650 °C. The creep behavior of the ODS steel could be understood by virtue of a dislocation creep deformation mechanism. Interrupted creep experiments under 100 MPa were conducted to further study the microstructure evolution during long-term creep deformation. The grains began to refine at the initial stage, and some M23C6 phases were observed at grain boundaries, which enhanced the microhardness during the first creep stage. Along with creep, both Y2O3 and Cu-rich precipitates exhibited good coherence with the matrix. The Y2O3 precipitates showed better thermal stability than the Cu-rich phase. During the second creep stage, some cavities emerged around the M23C6 phase and at grain boundaries. The cavities gradually developed into significant cracks, causing the steel to fracture. The creep damage due to cavity growth could be determined according to the creep damage tolerance factor value.

Creep damage mechanism of 20Cr32Ni1Nb steel at high temperatures

In the petrochemical industry, the centrifugally cast austenitic 20Cr32Ni1Nb stainless steel used in steam reformer furnace's hot outlet manifold experiences creep failure and microstructural degradation, impacting its structural integrity. Understanding the causes of these issues is crucial for addressing the associated challenges. This study examines the creep deformation behaviour, damage mechanisms, and microstructural evolution of 20Cr32Ni1Nb steel under stresses of 22–50 MPa at temperatures of 1163 K (890 °C) and 1223 K (950 °C). Analysis of creep and creep strain rate curves revealed the presence of both primary and tertiary creep stages, with the power law relationship governing the stress-dependent minimum creep rate and rupture life. The variance of creep damage tolerance factor was also analysed, with results showing that in high-stress regimes, loss of section and necking along with cavity growth may initiate tertiary creep, while in low-stress regimes, microstructural degradation, specifically G-phase formation, may initiate tertiary creep. As the duration of creep exposure increases, microstructures were observed to degrade, with the growth and coarseness of NbC and M23C6 carbides. The structure of the space group for the Ni–Nb–Si enriched G-phase in 20Cr32Ni1Nb steel was found to be Fm3‾m, with a lattice parameter of about 1.14 nm.