ABSTRACT A comprehensive study was conducted on high-temperature thermal stability of a multifunctional injection-molded polyphenylene sulfide (PPS)-matrix composite containing random short carbon fibers (CFs), graphite flakes (Gr), and polytetrafluoroethylene (PTFE) particles. Specimen were heated to 98–200°C for up to 48 h and examined for oxidative-reaction-induced changes. Thermal stability on morphology and chemical composition of the thermoplastic composite is first investigated, using differential scanning calorimetry (DSC) and X-ray diffraction (XRD). Negligible changes are found in the composite glass transition temperature, crystallinity, and melting temperature after up to 48 h of high-temperature exposure. The study further finds no change in the composite microstructure and chemical composition, under sustained high-temperature exposure. Therefore, results obtained in the study with DSC, optical microscopy, scanning electron microscopy, and XRD indicate that the CF/Gr/PTFE/PPS composite remains thermally stable in high-temperature environment.
ABSTRACT Improvements in dielectric properties, energy density, and charge–discharge efficiency pave the way for scalable, efficient solutions for modern energy storage systems and applications. The present review offers an outline of the very recent developments of ferroelectric (FE) polymer composite materials specifically for energy storage applications. It is focused on material innovations, structural design, and processing techniques. It also covers the composition of materials, integration techniques, and characteristics of emerging materials. The dielectric breakdown strength, energy storage density, power density, discharge speed, and thermal stability of the developed composite materials are conversed. This review discusses the impact of recent production techniques such as interface engineering and optimization, multilayer and core–shell structures on the characteristics of the FE polymer composite materials. The second part focuses on effective strategies for integrating polymers with FE ceramics to enhance energy storage performance. In the concluding section, the study critically reviews the limitations and challenges associated with these recent developments, while also highlighting future research directions and the scientific advancements required for the effective utilization of FE polymer composites as a high-performance energy storage material.
The information provided by today's standardized test methods used to assess the environment-induced cracking (EIC) sensitivity of high-strength 7xxx series Al-Zn-Mg-Cu alloys fails to provide the quantitative data needed for engineering design and service-lifetime prediction. Current EIC test output is qualitative in nature and is based on historical comparisons. The environmental test conditions and initial alloy surface conditions used are not related/relevant to those anticipated during commercial use. The reported in-service EIC issues for the current latest generation of Al-Zn-Mg-Cu alloys repeat the 1960's experience of "unexpected" major service failure issues for AA7079-T651 components. There is a critical need for EIC test methods that consistently differentiate EIC susceptibilities for relatively resistant alloy tempers in a reasonable time frame that are directly relatable to service performance. A novel test method is proposed to quantitatively assess an alloy's inherent EIC sensitivity.
Abstract Corrosion fatigue is a major damage mechanism responsible for the premature failure of the aircrafts and turbine parts, especially in the marine environment. The process starts with the surface degradation caused by the corrosion pits, which become fatigue initiation sites for the initial damage when the part is loaded. Microstructure and morphology of the surface pits is critical for the crack initiation. Cracks are initiated at sharp corners and at the bottoms of the narrow “micropits.” The paper provides a statistical characterization of the crack initiation process based on the pit density and microstructure distribution. Based on the analysis of surface damage initiation, new morphological characteristics combining pit size and highest curvature are introduced. The distribution of these introduced morphological characteristics is estimated from the measured data and have exhibited to be an efficient metric for pitting fatigue. The effects of pitting morphology are evaluated for various heat-treated 2024 aluminum alloy specimens with varying distribution of pit shapes and curvatures. The statistical distribution of specimen life is estimated using the “weakest link” approach; that is, by computing the probability that at least one crack is initiated somewhere on the surface. The paper contains a detailed description of crack initiation’s statistical model, the methodology for corrosion parameter estimation and representative numerical examples of statistical modeling. Surface pit characterization has been nondestructively measured on a Zygo ZeGage 3D surface profiler. The ZeGage uses a coherence scanning interferometry (CSI) technique based on the wavelength of light. This profiler can measure a wide range of surface qualities with repeatable results in sub-nanometer precision. Large-area scanning was done using a segmentation approach. A large field of view of the selected lens and automated rapid scanning allowed for reasonably smaller data files after stitching these individual segments.
The realization of a hydrogen economy depends on the development of robust infrastructure capable of safely storing and transporting hydrogen over long distances. Although new materials are constantly explored, significant efforts are also being made to repurpose existing pipeline infrastructure for hydrogen service. However, hydrogen embrittlement (HE) of metallic materials poses a critical challenge to this transition. Therefore, there is a strong need for accelerated testing methodologies to efficiently screen materials for hydrogen applications. The in situ small punch test (SPT) is well-suited for this purpose, owing to its minimal sample size, low hydrogen volume requirements, and the ability to conduct multiple tests safely. In this study, the gaseous HE behavior of pipeline steel API-X70 was investigated using the in situ SPT. The effects of hydrogen precharging time, punch velocity (strain rate), and hydrogen gas pressure on the embrittlement response were systematically examined. The results demonstrate that strain rate has a more pronounced impact on embrittlement than precharging time. Fractographic analysis of hydrogen-exposed samples shows characteristic features of embrittlement, including radial and circumferential cracks. Interestingly, the precharged samples exhibited extensive circumferential cracking, whereas samples tested under slow strain rates showed highly localized deformation with fewer secondary circumferential cracks. The degree of fracture localization was also found to increase with higher hydrogen gas pressures. This work provides detailed insight into the mechanisms driving HE in pipeline steel X70 by considering the interplay between hydrogen concentration, diffusivity, and strain rate during deformation.
The current framework for the safety assessment of ferritic ductile cast iron (DCI) containers used for the transport and storage of radioactive materials is based on the principles of fracture mechanics. Advisory Material for the IAEA Regulations for the Safe Transport of Radioactive Materials (2018 Edition), Appendix V: Guideline for the Safe Design of Packages against Brittle Fracture, the primary criterion is the prevention of crack initiation, and the design should not rely on any predicted ductile tearing resistance. Similarly, the ASME Code, Sect. III, Div. 3, explicitly deals with DCI and requires safety proof for dynamic loading conditions. However, the information provided in the guidelines does not appear sufficient for appropriately performing such dynamic fracture mechanics safety assessments. The ongoing German research project MCGUSS, Investigation of the Master Curve Concept for Ferritic Ductile Cast Iron, Subproject BAM Berlin: Investigations Using SE(B) Specimens (Contract No. 1501651), Subproject MPA Stuttgart: Investigations Using C(T) and DC(T) Specimens (Contract No. 1501650), is designed to address this issue. MCGUSS systematically investigates the application potential of the probabilistic fracture mechanics master curve (MC) concept according to ASTM E1921, Standard Test Method for Determination of Reference Temperature, T0, for Ferritic Steels in the Transition Range, and identifies potential modifications specific to the dynamic brittle fracture of DCI. Although MCGUSS covers testing of a large number of SE(B)-and C(T)-type specimens, this paper initially focuses on SE(B) results only. It presents the production of the test material and its properties. Particular focus is given to the fracture mechanics test facilities for dynamic small-and large-scale testing. The obtained data were statistically analyzed, and the results of the MC analyses are discussed. Particular emphasis is placed on using optical and scanning electron microscopy to link microstructural damage and failure processes to the fracture toughness data obtained. For the description of the established dynamic toughness data, a fracture mechanism called "specimen size-dependent arrest of local brittle fractures before global brittle failure by the weakest link" is proposed. Regarding the MC concept, it was demonstrated that the ASTM E1921 procedure cannot be directly applied to dynamic DCI toughness data. Material-specific modifications are being investigated, and the DCI dynamic fracture toughness database is being expanded.
The development of efficient thermal energy storage (TES) materials is vital for improving energy utilization and supporting renewable and industrial heat recovery systems. conductivity and poor interfacial wettability, which limit heat-transfer efficiency and storage performance. This study investigates the effect of multi-walled carbon nanotube (MWCNT) doping on the thermophysical and interfacial properties of lithium-based eutectic salts with different compositions-binary (LiK), ternary (LiT), and quaternary (LiQ). The results show that low MWCNT concentrations (0.1-0.3 wt.%) enhanced latent heat by up to 8 % and thermal conductivity by 12-15 %, whereas specific heat showed modest improvement. Contact angle analysis indicated a significant decrease in surface angle, confirming improved wettability and stronger interfacial heat transfer. Scanning electron microscopy images revealed uniform nanoparticle dispersion and compositional stability, confirming the chemical compatibility of the nanocomposite salts. These findings demonstrate that optimized MWCNT incorporation eutectic salts. The study provides comparative and mechanistic insights into the role of nanocarbon doping in improving the performance of molten-salt PCMs, offering a pathway for the design of advanced TES materials with improved efficiency and stability. The novelty of this study lies in its comparative evaluation of MWCNT-doped lithium-based binary, ternary, and quaternary eutectic salts under identical conditions, and in correlating interfacial wettability with thermophysical enhancements. This integrated approach establishes a mechanistic understanding of how carbon nanostructures modify molten-salt behavior. The findings provide a scientific framework for designing next-generation PCMs with improved efficiency and reliability for high-temperature TES applications.
Studies have shown that the Delta Kth,i versus 6* relationship can be used to interpret load sequence effects in early fatigue crack growth under flight-spectrum loading. The objective of this study is to determine whether this applies to load history effects in early crack growth when elevated temperature with and without associated corrosive environment is involved. Tests were performed to establish the Delta Kth,i versus 6* relationship for Waspaloy at 650 degrees C in air and in rarified nitrogen. Experiments were performed to study load sequence effects on early fatigue crack growth in the same material using specially designed programmed loads designed to induce contrasting levels of near-tip residual stress through periodic overloadunderload sequences. These are followed by quantitative fractography of the fatigue fracture surfaces in order to investigate whether observed load sequence effects on crack growth rate can be explained by the Delta Kth,i versus 6* relationship.
The crystallographic texture effect on fatigue endurance anisotropic behavior was evaluated for an API 5L X42 pipeline steel among longitudinal (L-0 degrees), diagonal (D-45 degrees), and circumferwhich presented the lowest degree of banding (Ai) and grain orientation (Omega 12), as well as a larger number of grains oriented parallel to {110} planes. Therefore, fatigue life anisotropy is mainly controlled by the synergistic interaction between pearlite banding degree (Ai) and crystallographic texture. Also, it is foreseen that the observed behavior can be related to the dislocation arrays generated by cyclic loading in relation to microstructure orientation.
This paper reports an investigation of fatigue phenomena in Weir's GEHO fluid end pump components, made of carbon steel materials exposed to corrosive environments and subjected to cyclic stresses. The research involved the development of a numerical simulation framework built to model corrosion fatigue mechanisms, supported by advanced crack growth simulations. Validation of the methodology was achieved through simulations of plane uniaxial specimens, U-shaped notched specimens, and lab-scale pressure component, showing a high degree of correlation between predicted and experimental results-both in terms of crack propagation paths (striation patterns) and fatigue life (number of cycles). Following this robust validation, the framework was applied to simulate crack growth and assess the fatigue lifetime of a positive displacement pump diaphragm housing component. The nCode software was used to identify critical locations, or hot spots, where initiation is most likely to occur. Subsequently, MSC Marc/Mentat was employed to perform advanced simulations of crack propagation under complex loading conditions. In addition to identifying critical points, an analysis of the crack growth orientation influenced by applied cyclic loading was also conducted. This application demonstrates the potential to accurately predict corrosion fatigue performance in complex real-world geometries, reducing the need for costly full-scale experimental testing. The findings provide practical insights into the durability and reliability of carbon steel parts operating under cyclic loading conditions in corrosive environments. The results have broader implications, offering valuable guidance not only for the design and maintenance of mineral processing pump components but also for a wide range of industrial sectors, including power generation and marine engineering.
The effect of microstructural aging on fatigue endurance of an API 5L X70 pipeline steel was evaluated. Results showed that fatigue life is clearly dependent on aging time and, hence, on microstructural degradation attributed to long-term service. This behavior is associated with the morphological evolution of cementite inside the ferrite grains, transforming from platelets to elongated and spherical particles, and finally into flaky particles. Similarly, cementite at the grain boundaries transforms into spheroidized cementite, facilitating the appearance of sliding bands and thus the extrusion and intrusion formation. The interactions of the fatigue crack tip with the microstructure during the crack propagation stage have a significant effect on fatigue life.
In this work, Ca and Fe co-doped BaTiO3 ceramics with compositions Ba1-xCaxTi1-yFeyO3 with varying compositions (x, y = 1, 1.5, and 2 mol %) were prepared via a solid-state synthesis method and sintered at 1,000 degrees C. This study investigates the influence of A-site (Ca) and B-site (Fe) substitutions on phase structure, microstructure, and magnetic properties at room-temperature. X-ray diffraction confirmed a pure tetragonal perovskite phase without any secondary phases. The diffraction peaks exhibited a systematic shift to higher 2 theta angles with increasing temperature because of the substitution of smaller Ca2+ and Fe3+ ions into the BaTiO3 lattice. Scanning electron microscopy analysis reveals significant grain change with increasing co-doping concentration, where the average grain size decreases from approximately 469 nm at 1 % doping to about 171 nm at 2 % doping. Energy dispersive X-ray spectroscopy (EDS) confirmed the successful incorporation of Ca and Fe into the BaTiO3, confirming their successful substitution into the lattice without detectable impurities. The vibrating sample magnetometer (VSM) data show a weak ferromagnetism at 300 K, with Ms rising from 0.033 emu/g at 1 % doping to 0.067 emu/g at 2%, demonstrating enhanced magnetic response at higher doping. These findings demonstrate that Ca/Fe co-doping leads to room-temperature magnetic ordering in BaTiO3 while maintaining its ferroelectric phase, thereby producing a multiferroic material. Overall, this research provides a potential method for creating lead-free multiferroic ceramics aimed at future applications in spintronics and magnetoelectric device technologies.
Al-Mg alloys have a prominent role for applications in the marine, transportation, and civil industry because of their moderate strength, corrosion resistance, and weldability. In this study, the microstructure, densification characteristics, and microhardness variation of Al-5 Mg (wt%) alloy have been studied in connection with the response to rolling of induction sintered alloy. Sintering at a moderate heating rate (4 C degrees/s) and 550 degrees C for 3 min resulted in relatively low density (72 %) and hardness (50 HV) and also the segregation of Mg during cooling at grain-boundaries of alpha-Al, which is connected with an enhance in lattice parameter with a value of 0.4055 nm. In absence of segregation, after solutionizing at 550 degrees C for 2 h and water quenching, the sample demonstrated higher density and microhardness with values of 92 % and an average microhardness of 100 HV, with a decrease in the lattice parameter with value of 0.4039 nm. The solutionized alloy responded to hot rolling with thickness reduction of 20 %. However, in the case of the solutionized-quenched sample followed by annealing at 550 degrees C for 1 h, hot or cold rolling was not successful. This may be attributed to the formation of hot cracking during annealing along grain-boundaries in the presence of the residual porosity in the quenched sample. The cracking mode can be attributed to ductility dip cracking, which is typically observed at annealing temperatures, in which the alloy always suffers a rapid reduction in ductility. Solutionized-hot-rolled alloy resulted in improvement in density and microhardness with values of 94 % and 140 HV and a decrease in the lattice parameter with a value of 0.4036 nm.
This study presents a comprehensive thermal analysis of autogenous tungsten inert gas welding on a 316 LN stainless steel plate, integrating experimental techniques and finite element simulation. The Goldak double ellipsoid heat source model is employed to simulate the heat input accurately. Experimental measurements are conducted using both contact (using K-type thermocouples) and noncontact infrared (IR) thermography methods, comparing their effectiveness in capturing precise thermal gradients and validating the numerical predictions. The peak temperature in the adjacent base metal at a distance of 10 mm from the weld centerline obtained from finite element analysis (FEA) is 527 degrees C, whereas that obtained using the thermocouple and IR thermography are 507 degrees C and 513 degrees C, respectively. The FEA predicted molten weld pool temperature to be 1,970 degrees C, which closely matches with the IR recorded temperature of 1,800 degrees C. The simulation demonstrated high accuracy, with the peak melt pool temperature measured by IR and the peak temperature at the base plate measured using both IR and thermocouples showing a deviation within 10 %. Along with validating computational predictions of weld pool temperature, the IR thermography was also used successfully to estimate the weld-bead width. The fusion zone half-width from the experimental macrograph analysis is 3.2 +/- 0.05 mm, which agrees well with the simulation (3.2 mm) and IR thermography (3.6 mm). Additionally, the study explores the effect of varying convection heat transfer coefficient on cooling rate. This integrated approach results in more accurate welding simulations, which can act as the foundation for residual stress analysis and for optimizing the welding parameters. The novelty of this work lies in the combined use of thermocouple, IR thermography, and FE simulation for weld thermal analysis, achieving <= 10 % deviation in thermal history predictions and bead-width estimation within similar to 12 % of the measured values.
This study reports the development of heavy-section hollow rectangular forgings of aluminum alloy AA2219 in T852 temper with a ruling section thickness of 360 mm and establishes the associated processing-microstructure-property relationships. Traditional solid forgings of this size often suffer from quench sensitivity, where the slow cooling of the inner core leads inconsistent mechanical properties. Unlike conventional solid thick-section forgings, the present work introduces a premachining-assisted hollow configuration prior to heat treatment to mitigate quench sensitivity and improve through-thickness property uniformity. An optimized open-die forging route was designed to control material flow, strain distribution, and thermal history during processing. Detailed microstructural characterization reveals uniform grain flow patterns and refined microstructural features across the section, which directly contribute to the enhanced mechanical performance. The results demonstrate that this hollow core approach ensures total ultrasonic integrity and meets strict aerospace standards for mechanical performance, providing a scalable solution for manufacturing large-scale structural components.
The short lifespan and frequent machine downtime because of wear of copper electrodes in resistance welding are major issue in fin-tube welding for waste heat recovery boilers. To address this, a Cu-Cr-Zr alloy was developed as an alternative to electrolytic tough pitch (ETP)-Copper electrodes for H-type fin welding. The alloy was synthesized by melting electrolytic copper, chromium powder, and zirconium chips at 1,100 degrees C-1,300 degrees C, followed by hot forging and aging at 450 degrees C for 120 min. This process significantly improved the alloy's microstructure, mechanical properties, and electrical conductivity. The Cu-Cr-Zr alloy achieved a tensile strength of 426 MPa, elongation above 18 %, and electrical conductivity over 86.5 % International Annealed Copper Standard. Microstructural analysis revealed fine, equiaxed grains from multistage deformation and aging, enhancing grain boundary density and reducing lattice distortion, which improved conductivity. In performance tests, the Cu-Cr-Zr alloy's life-span is 20 times longer than that of ETP-Cu in H-type fin-to-tube welding.
Hydrogen embrittlement is a major concern in the fastener and automotive industry, particularly when it comes to strength levels above 1,000 MPa. The properties of ultra-high-tensile-strength (UHT) fasteners, classified in strength grades 12.9U-17.8U, are achieved through enhanced requirements on chemical composition and an austempering process that results in a bainitic microstructure. As a result, the risk of hydrogen-induced brittle fracture from hydrogen uptake during corrosion in the field is mitigated, despite the bolts' high strength. A novel approach proposed by the authors further enhances the bolts' resistance to hydrogen-induced brittle fracture. This is achieved by applying a Ni plating before heat treatment, thereby modifying the metallic surface layer, which then acts as a hydrogen barrier, effectively protecting the fasteners even in environments with elevated risks of hydrogen uptake. The present investigation demonstrates that the hydrogen embrittlement resistance of these fasteners surpasses current state-of-the-art solutions.
The increasing demand for high-strength, corrosion-resistant steels in advanced engineering applications has driven the search for materials that eliminate hazardous coatings like cadmium while maintaining robust mechanical performance. This study investigates the effect of carburization on the microstructure, corrosion behavior, and surface hardness of the CSS-42L stainless steel. Under sulfur dioxide salt fog testing, noncarburized CSS-42L coupons exhibited no signs of general or localized corrosion across combined galvanic and crevice, galvanic, and individual exposure conditions. In contrast, carburized CSS-42L samples displayed general corrosion on flat surfaces, pitting along sidewalls, and edge cracking, with a significant increase in the corrosion rate compared with the equivalent untreated samples. Microstructural analyses via optical microscopy confirmed a gradient in the carburized samples, from a high-carbon martensitic surface enriched with M7C3 and M23C6 carbides to a tempered martensitic core. Electron backscatter diffraction phase maps also revealed carbide morphologies and distribution. Hardness profiles further corroborated these gradients, with surface values reaching approximately 785 HV compared with approximately 360 HV for the core, matching the uniform hardness of noncarburized samples. Overall, the results demonstrate that although carburization enhances surface hardness, it compromises corrosion resistance due to chromium depletion and carbide precipitation. These findings underscore the design potential and limitation of selective carburization strategies to enhance mechanical performance.
The present study investigated the performance of ceramic aluminum oxide (Al2O3) and yttrium oxide (Y2O3) coatings along with a combined Y2O3 and tungsten (W) coating as high-temperature permeation barriers. To evaluate the permeability, these coatings were applied using the physical vapor deposition (PVD) process onto a palladium membrane. The hydrogen permeability of the three coatings was assessed using both absorption and permeation test methodologies between 300 degrees C and 400 degrees C. Results indicated that at 300 degrees C, the Y2O3 coating has the most stable performance at various delta pressures with hydrogen permeation below the detection limit of the measurement system. Although the dual coating of Y2O3 + W is stable at lower pressure range, it seems to become ineffective at a pressure above 700 Pa. Al2O3 reduces hydrogen permeability compared to the pure Pd but the hydrogen permeability increases as the pressure increases in the same trend as the pure Pd sample. The bond strength of the PVD coatings to a low activation ferritic martensitic steel substrate was successfully evaluated through scratch testing. The P91 steel substrate surface was laser textured to 1 mu m in order to study the effect of surface roughness on the interface bonding strength. The untextured surface showed clear cohesive and adhesive fractures, whereas the laser-textured surfaces exhibited higher resistance to fractures. Among the tested coatings, the Al2O3 coating demonstrated the highest bond strength.
Corrosion under insulation (CUI) refers to degradation of metals under thermal insulations, which reportedly manifests as localized corrosion and pitting. The ASTM standard for the laboratory simulation of CUI (i.e., ASTM G189-07, Standard Guide for Laboratory Simulation of Corrosion under Insulation) proposes an annular gap between insulation and steel coupons to accommodate the counter electrode (CE) to allow for electrochemical measurements. On the other hand, annular gap deprives the proposed arrangement in ASTM G189-07 from oxygen concentration cells that otherwise exist in real-world applications from the direct contact between insulation and steel. Also, there is a literature gap in understanding the long-term implications of direct contact between insulation and steel and consequential oxygen concentration cells, which are crucial for pitting under thermal insulations. This research investigates CUI simulation behavior via direct contact between insulation and steel (i.e., no annular gap) while allowing for electrochemical measurements by incorporating a novel method deploying carbon fiber mesh as CE. Generally, the presence of pitting can greatly affect the rates of CUI in a nonlinear manner. The standard duration for CUI simulation tests has been 72-96 hours (3-4 days), which may not trigger noticeable localized corrosion and pits, especially when insulation grades with corrosion inhibitors are involved. Moreover, short-duration tests may not trigger insulation aging and consequential corrosive leaching that occur otherwise in real-world applications. This study also investigates CUI rates and corrosion modes over longer durations, specifically 15 and 30 days. Following the CUI simulation tests, corroded surfaces were characterized using confocal laser scanning, 3-D topography, and scanning electron microscopy to understand the impact of direct contact versus annular gap as well as corrosion behavior over longer durations from a CUI rate perspective. Finally, the research suggests some improvements to ASTM G189-07 in terms of test setup and characterizations.
