Materials

15 pages, 4604 KiB

Open AccessArticle

Preparation, Thermal, and Optical Properties of D-A-Type Molecules Based on 1,3,5-Triazine for Violet-Blue Fluorescent Materials

by Lu Wang, Enwang Du, Zhi Liu and Zhiqiang Liu

Materials 2025, 18(9), 2043; https://doi.org/10.3390/ma18092043 (registering DOI) - 29 Apr 2025

Abstract

Organic violet-blue fluorescent materials have garnered significant interest for a broad spectrum of applications. A series of triazine-based molecules, that is, 2,4,6-tri(9H-carbazol-9-yl)-1,3,5-triazine (TCZT), 2,4,6-tri(1H-indol-1-yl)-1,3,5-triazine (TIDT), and 2,4,6-tris(3,6-di-tert-butyl-9H-carbazol-9-yl)-1,3,5-triazine (TDBCZT), exhibiting violet-blue emission were synthesized via a catalyst-free aromatic nucleophilic substitution reaction. These compounds possess [...] Read more.

Organic violet-blue fluorescent materials have garnered significant interest for a broad spectrum of applications. A series of triazine-based molecules, that is, 2,4,6-tri(9H-carbazol-9-yl)-1,3,5-triazine (TCZT), 2,4,6-tri(1H-indol-1-yl)-1,3,5-triazine (TIDT), and 2,4,6-tris(3,6-di-tert-butyl-9H-carbazol-9-yl)-1,3,5-triazine (TDBCZT), exhibiting violet-blue emission were synthesized via a catalyst-free aromatic nucleophilic substitution reaction. These compounds possess a non-planar and twisted structure with favorable charge-transfer characteristics, demonstrating excellent thermal stability (decomposition temperatures of 370 °C, 384 °C, and 230 °C, respectively). Cyclic voltammetry analysis, combined with time-dependent density functional theory (TD-DFT) calculations at the B3LYP/6-31G(d) level, offered detailed insights into their electronic structures and electrochemical properties. Optical properties were systematically characterized using Ultraviolet–visible (UV–Vis) absorption and photoluminescence (PL) spectroscopy. The compounds exhibited violet-blue luminescence with emission peaks located at 397 nm, 383 nm, and 402 nm in toluene, respectively. In their respective films, the compounds exhibited varying degrees of spectral shifts, with emission peaks at 408 nm, 381 nm, and 369 nm. Moreover, the CIE (Commission Internationale de l’Éclairage) coordinates of TIDT in toluene were (0.155, 0.067), indicative of excellent violet purity. These compounds demonstrated significant two-photon absorption (TPA) properties, with cross-sections of 4.6 GM, 15.3 GM, and 7.4 GM, respectively. Notably, they exhibited large molar absorptivities and substantial photoluminescence quantum yields (PLQYs), suggesting their potential for practical applications as violet-blue fluorescent materials. Full article

(This article belongs to the Section Optical and Photonic Materials)

25 pages, 18977 KiB

Open AccessArticle

Development of a Color-Changing Face Mask for Fever Detection Applications

by Nareerut Jariyapunya, Sunee Hathaiwaseewong, Nanjaporn Roungpaisan and Mohanapriya Venkataraman

Materials 2025, 18(9), 2042; https://doi.org/10.3390/ma18092042 (registering DOI) - 29 Apr 2025

Abstract

This study focused on developing a color-changing fabric face mask for fever detection. Reversible Thermochromic Leuco dye (RTL) was applied as an indicator to alert wearers of elevated body temperatures, with the color change occurring at 37.5 °C. Five fabric types Polyethylene (PE), [...] Read more.

This study focused on developing a color-changing fabric face mask for fever detection. Reversible Thermochromic Leuco dye (RTL) was applied as an indicator to alert wearers of elevated body temperatures, with the color change occurring at 37.5 °C. Five fabric types Polyethylene (PE), cotton (CO), a cotton–polyester blend (TC), polyester (PL), and Polyamide (PA) were coated with blue RTL to evaluate their color change responsiveness. The results showed that fabrics with higher thermal conductivity (λ), thermal absorptivity (b), and heat flow (q) exhibited faster color transitions. RTL-coated PE fabric demonstrated the best performance, with a thermal absorptivity of 312.8 Ws^0.5m⁻²K⁻¹ and a heat flow of 2.11 Wm⁻², leading to a rapid color-change time of approximately 4.20 s. Although PE fabric had a lower thermal conductivity (57.6 × 10⁻³ Wm⁻¹K⁻¹) compared to PA fabric 84.56 (10⁻³ Wm⁻¹K⁻¹), the highest thickness 0.65 mm of PA fabric slowed its color-change reaction to 11.8 s. When selecting fabrics for optimal heat transfer, relying solely on fiber type or thermal conductivity (λ) is insufficient. The fabric’s structural properties, particularly thickness, significantly impact thermal resistance (γ). Experimental results suggest that thermal absorptivity and heat flow are more effective criteria for fabric selection, as they directly correlate with color-change performance. Full article

(This article belongs to the Special Issue Synthesis–Processing–Structure–Property Interrelationship of Multifunctional Polymeric Materials and Natural Polymers)

14 pages, 1596 KiB

Open AccessArticle

Performance Evolution and Damage Evaluation of CRTS I Track Slab in Service Status

by Hongyao Lu, Wentao Wu and Yuelei He

Materials 2025, 18(9), 2041; https://doi.org/10.3390/ma18092041 (registering DOI) - 29 Apr 2025

Abstract

This study develops a quantitative framework to assess performance degradation and damage evolution in CRTS I ballastless track slabs. Based on the impact-echo method, the internal void distribution characteristics of the new and old track slabs were obtained. The track slabs were sampled [...] Read more.

This study develops a quantitative framework to assess performance degradation and damage evolution in CRTS I ballastless track slabs. Based on the impact-echo method, the internal void distribution characteristics of the new and old track slabs were obtained. The track slabs were sampled separately by drilling cores to verify the distribution of voids, and uniaxial compression tests were conducted simultaneously to quantify the attenuation of bearing capacity. The on-site wheel–rail force and temperature field data were monitored, based on the established three-dimensional finite element model of CRTS I ballastless track, and the damage distribution characteristics of the track slab under different load combinations after performance degradation were studied. The results show the following: (1) As the performance of the track slabs gradually deteriorated, it was reflected in the increasing internal void distribution area from 0.5% to 3.6%, corresponding to a 22.4% decrease in core strength. (2) The on-site monitoring results showed that the average wheel–rail force was 84.5 kN. The temperature gradient range varied from -50.4 °C/m to 100.0 °C/m, exceeding the allowable value of the design specifications. (3) The actual damage distribution of the track slab after performance degradation under different load combinations significantly increased at key stress locations such as near fasteners, convex abutments, and anchor holes of prestressed steel bars, which required special attention in actual maintenance and repair. Full article

(This article belongs to the Section Construction and Building Materials)

15 pages, 1296 KiB

Open AccessArticle

Selenium-Containing Multi-Resonance Thermally Activated Delayed Fluorescence Host Material for Green and Red Phosphorescent OLEDs

by Hyukmin Kwon, Seokwoo Kang, Sangwook Park, Saeyoung Oh, Sang-Tae Kim, Kiho Lee, Hayoon Lee and Jongwook Park

Materials 2025, 18(9), 2040; https://doi.org/10.3390/ma18092040 (registering DOI) - 29 Apr 2025

Abstract

We report the molecular design and synthesis of a novel selenium-containing multi-resonance thermally activated delayed fluorescence (MR-TADF) host material, 3,6-di-tert-butyl-9,16-dioxa-15-selena-4b-boraindeno[2,1-a]naphtho[3,2,1-de]anthracene (TDBA-SePh), for green and red phosphorescent organic light-emitting diodes (PhOLEDs). By incorporating selenium into the DOBNA-based MR-TADF backbone, the reverse intersystem crossing (RISC) [...] Read more.

We report the molecular design and synthesis of a novel selenium-containing multi-resonance thermally activated delayed fluorescence (MR-TADF) host material, 3,6-di-tert-butyl-9,16-dioxa-15-selena-4b-boraindeno[2,1-a]naphtho[3,2,1-de]anthracene (TDBA-SePh), for green and red phosphorescent organic light-emitting diodes (PhOLEDs). By incorporating selenium into the DOBNA-based MR-TADF backbone, the reverse intersystem crossing (RISC) process was effectively activated, leading to enhanced utilization of triplet excitons. The corresponding RISC rate was determined to be 3.91 × 10⁴ s⁻¹. When applied to PhOLED devices, TDBA-SePh-based green and red OLEDs exhibited higher external quantum efficiency (EQE) and reduced efficiency roll-off compared to conventional mCP-based host materials. At a luminance of 1000 cd m⁻², the green and red devices exhibited roll-off values of 2.5% and 4.3%, respectively. This improvement is attributed to the incorporation of selenium as a heteroatom, which accelerates the RISC process, thereby suppressing triplet-triplet annihilation (TTA). These results suggest that adopting a similar molecular design strategy can not only reduce efficiency roll-off but also enhance device efficiency and operational stability, offering significant potential for future OLED applications. Full article

(This article belongs to the Special Issue Enhancement Strategies for High External Quantum Efficiency of Organic Light Emitting Diodes (OLEDs) and the Analyses)

24 pages, 16143 KiB

Open AccessArticle

Influence of UV Radiation on the Appearance Quality of Fair-Faced Concrete and Mitigation Approaches

by Ao Wu, Jia Ke, Zhijie Liu and Zhonghe Shui

Materials 2025, 18(9), 2039; https://doi.org/10.3390/ma18092039 (registering DOI) - 29 Apr 2025

Abstract

Fair-faced concrete has garnered substantial attention in recent years owing to its aesthetic appeal and eco-friendly attributes. However, as a construction material, its long-term performance is highly dependent on its service environment, particularly ultraviolet (UV) radiation. This research focuses on examining the influence [...] Read more.

Fair-faced concrete has garnered substantial attention in recent years owing to its aesthetic appeal and eco-friendly attributes. However, as a construction material, its long-term performance is highly dependent on its service environment, particularly ultraviolet (UV) radiation. This research focuses on examining the influence of UV exposure and managing the admixtures employed in concrete and investigating the effects of UV radiation on the appearance quality, pore distribution, and micro-composition of fair-faced concrete. Results indicate that UV radiation enhances moisture evaporation, increases surface and bulk porosity, and accelerates carbonation and early hydration reactions, forming more calcite on the surface. These factors degrade the appearance quality of fair-faced concrete. To mitigate UV-aging damage, two common anti-UV admixtures, nano-silica (NS) and water-based fluorocarbon paint (FC), were evaluated. Results show that both admixtures effectively improve the UV-resistance of fair-faced concrete, particularly when combined. The FC+NS group reduced the surface glossiness loss rate from 28.63% to 12.95% after 28 days of UV exposure, with surface porosity and maximum pore diameter recorded at 0.157% and 3.66 mm, respectively, indicating excellent appearance quality. These findings underscore the potential of these admixtures, both individually and in combination, to enhance the UV resistance of fair-faced concrete, sustaining its durability under prolonged UV exposure. Full article

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17 pages, 6625 KiB

Open AccessArticle

Mechanical Properties of Aluminum Alloy Tubes Fabricated Through Surface Mechanical Grinding Treatment and Graphene Lubrication Under Biaxial Stress States

by Yang Cai, Xiao-Lei Cui, Chunhuan Guo, Fengchun Jiang and Piaoping Yang

Materials 2025, 18(9), 2038; https://doi.org/10.3390/ma18092038 (registering DOI) - 29 Apr 2025

Abstract

To enhance the mechanical properties of 6063-T4 aluminum alloy tubes, surface mechanical grinding treatment was conducted under graphene-assisted lubrication. The effects of rotational speed and cooling conditions on the mechanical properties of aluminum alloy tubes under biaxial stress were systematically explored. It was [...] Read more.

To enhance the mechanical properties of 6063-T4 aluminum alloy tubes, surface mechanical grinding treatment was conducted under graphene-assisted lubrication. The effects of rotational speed and cooling conditions on the mechanical properties of aluminum alloy tubes under biaxial stress were systematically explored. It was found that increasing the rotational speed and cooling rate facilitates the formation of finer lamellar grains, higher-density nano-precipitates, and a reduced dislocation density on the tube surface. These microstructural characteristics significantly contribute to an increased yield strength and sustained strain hardening capacity during bulging deformation. This study proposes an innovative approach for improving the strength and toughness of light alloy components during integral forming, providing meaningful insights for future engineering applications. Full article

(This article belongs to the Special Issue Mechanical Performance and Microstructural Characterization of Light Alloys (2nd Edition))

3 pages, 149 KiB

Open AccessEditorial

Metallurgical Process Simulation and Optimization—2nd Volume

by Jiangshan Zhang, Jiali Tang and Qing Liu

Materials 2025, 18(9), 2037; https://doi.org/10.3390/ma18092037 (registering DOI) - 29 Apr 2025

Abstract

As the cornerstone of industrial civilization, metallurgical engineering has consistently driven materials innovation and advanced manufacturing technologies [...] Full article

(This article belongs to the Special Issue Metallurgical Process Simulation and Optimization—2nd Volume)

35 pages, 5269 KiB

Open AccessArticle

The Quantum Transport of Dirac Fermions in Selected Graphene Nanosystems Away from the Charge Neutrality Point

by Adam Rycerz

Materials 2025, 18(9), 2036; https://doi.org/10.3390/ma18092036 - 29 Apr 2025

Abstract

The peculiar electronic properties of graphene, including the universal dc conductivity and the pseudodiffusive shot noise, are usually found in a small vicinity close to the charge neutrality point, away from which the electron’s effective mass raises, and nanostructures in graphene start to [...] Read more.

The peculiar electronic properties of graphene, including the universal dc conductivity and the pseudodiffusive shot noise, are usually found in a small vicinity close to the charge neutrality point, away from which the electron’s effective mass raises, and nanostructures in graphene start to behave similarly to familiar Sharvin contacts in semiconducting heterostructures. Recently, it was pointed out that as long as abrupt potential steps separate the sample area from the leads, some graphene-specific features can be identified relatively far from the charge neutrality point. These features include greater conductance reduction and shot noise enhancement compared to the standard Sharvin values. The purpose of this paper is twofold: First, we extend the previous analysis based on the effective Dirac equation, and derive the formulas that allow the calculation of the arbitrary charge transfer cumulant for doped graphene. Second, the results of the analytic considerations are compared with numerical simulations of quantum transport on the honeycomb lattice for selected nanosystems for which considerations starting from the Dirac equation cannot be directly adapted. For a wedge-shaped constriction with zigzag edges, the transport characteristics can be tuned from graphene-specific (sub-Sharvin) values to standard Sharvin values by varying the electrostatic potential profile in the narrowest section. A similar scenario is followed by the half-Corbino disk. In contrast, a circular quantum dot with two narrow openings showing a mixed behavior appears: the conductance is close to the Sharvin value, while the Fano factor approaches the value characterizing the symmetric chaotic cavity. Carving a hole in the quantum dot to eliminate direct trajectories between the openings reduces the conductance to sub-Sharvin value, but the Fano factor is unaffected. Our results suggest that experimental attempts to verify the predictions for the sub-Sharvin transport regime should focus on systems with relatively wide openings, where the scattering at the sample edges is insignificant next to the scattering at the sample–lead interfaces. Full article

(This article belongs to the Special Issue Quantum Transport in Novel 2D Materials and Structures)

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16 pages, 3051 KiB

Open AccessArticle

Recycling End-of-Life Bituminous Membranes in Asphalt Mixtures: A Laboratory Study

by Marco Pasetto, Safeer Haider, Andrea Baliello and Emiliano Pasquini

Materials 2025, 18(9), 2035; https://doi.org/10.3390/ma18092035 - 29 Apr 2025

Abstract

The circular economy (i.e., reuse and recycling of waste materials) is gaining attention for the goal of achieving net-zero waste. In this regard, the use of waterproofing membrane waste in bituminous materials can be a valid option, as every year, a lot of [...] Read more.

The circular economy (i.e., reuse and recycling of waste materials) is gaining attention for the goal of achieving net-zero waste. In this regard, the use of waterproofing membrane waste in bituminous materials can be a valid option, as every year, a lot of bituminous membrane wastes are generated both as production scraps or end-of-life wastes. Given this background, the recycling feasibility of end-of-life bituminous membrane waste (MW) in asphalt mixtures was assessed in this research study. To this aim, MW shreds (≤20 mm) were added to dense-graded bituminous mixtures using the dry-mixing method. The shreds were dosed at 0.5% by the mix weight (mix coded as SH−) or at 2% by mix weight (mix coded as SH+). A corresponding reference mix without MW was also tested for comparison purposes. The mixtures’ workability, strength and stiffness as well as permanent deformation, moisture and fatigue resistance were evaluated. Overall, the laboratory experimental findings showed that MW-modified bituminous mixtures with a higher dosage of membrane waste (SH+) have relatively higher moisture resistance, fatigue resistance, stiffness and high-temperature performance with respect to the corresponding reference mix. Moreover, both the reference and MW-modified mixtures showed similar workability regardless of the MW content. Full article

(This article belongs to the Special Issue Innovative Materials and Technologies for Road Pavements)

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16 pages, 7782 KiB

Open AccessArticle

Microstructural Evolution and Internal Hydrogen Content of Ultra-High-Strength Automotive Steels During Two Typical Industrial Production Flows

by Zhiyuan Chang, Jingjing Yin, Long Li, Xingzhao Chen, Xinyi Ruan and Liangyun Lan

Materials 2025, 18(9), 2034; https://doi.org/10.3390/ma18092034 - 29 Apr 2025

Abstract

Hot stamping is a promising method to manufacture ultra-high-strength automotive steel components with high dimension accuracy. In this work, two actual industrial production flows (with and without Al-Si hot dipping) were investigated to reveal their microstructural evolution and hydrogen content at different production [...] Read more.

Hot stamping is a promising method to manufacture ultra-high-strength automotive steel components with high dimension accuracy. In this work, two actual industrial production flows (with and without Al-Si hot dipping) were investigated to reveal their microstructural evolution and hydrogen content at different production steps. Meanwhile, the variations in composition and phase structures of the Al-Si coating layer were studied in terms of energy-dispersive spectrometry and electron backscattering diffraction techniques. The results showed that the microstructure at the steel substrate changed from the pancake-shaped pearlite and ferrite, degenerated pearlite and annealed ferrite, lath martensite, and then tempered martensite with the progress of the production steps, which was not affected by the Al-Si hot dipping. The final coating layer exhibited a multi-sublayer structure with the alternative distribution of FeAl and Fe₂Al₅, which contained many microcracks on the brittle phase Fe₂Al₅. The Al-Si-coated specimens always had higher hydrogen content than the bare steel specimens because of the hydrogen generation at the hot stamping stage and hydrogen absorption during the hot-dip aluminizing stage. Full article

(This article belongs to the Section Manufacturing Processes and Systems)

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17 pages, 5128 KiB

Open AccessArticle

Effect of Temperature on Material Removal Rate During Shear-Thickening Polishing

by Zhong Yu, Jiahuan Wang, Jiahui Du, Lanying Shao and Binghai Lyu

Materials 2025, 18(9), 2033; https://doi.org/10.3390/ma18092033 - 29 Apr 2025

Abstract

Shear-thickening polishing (STP) technology achieves efficient processing by modulating the non-Newtonian properties of the slurry, while temperature has an important effect on its rheological behavior. To reveal the effect of temperature on material removal rate (MRR) during the shear-thickening polishing process, this study [...] Read more.

Shear-thickening polishing (STP) technology achieves efficient processing by modulating the non-Newtonian properties of the slurry, while temperature has an important effect on its rheological behavior. To reveal the effect of temperature on material removal rate (MRR) during the shear-thickening polishing process, this study measured the rheological profiles of the shear-thickening polishing slurry (STPS) at different temperatures and observed the rheological behavior using a high-speed video camera, as well as monitored the changes in the polishing force exerted on the workpieces, MRR, and the surface roughness. Experimental data show that the peak viscosity of the slurry in the shear-thickening state decreases from 0.81 Pa·s to 0.49 Pa·s as the temperature increases from 30 °C to 50 °C. High-speed video observations show that the wavy solid layer in the thickening area diminishes with increasing temperature, the distribution area shrinking, and nearly vanishing at 50 °C. When the temperature rises from 30 °C to 40 °C, the average polishing force at 30 min decreases from 25.3 N to 22.6 N by 10.6%. MRR decreases from 33.5 nm/min to 7.9 nm/min by 75.5%. The decrease in MRR is much greater than the polishing force. This study provides an experimental basis for the effect of temperature on STP. Full article

(This article belongs to the Section Manufacturing Processes and Systems)

18 pages, 5896 KiB

Open AccessArticle

Efficiency of Alternative Reinforcement Methods for Wooden Ceilings and Their Ecological Aspects

by Karl Deix, Christian Huber and Josip Gogic

Materials 2025, 18(9), 2032; https://doi.org/10.3390/ma18092032 - 29 Apr 2025

Abstract

In the case of load increases and the refurbishment of existing buildings, it is often necessary to carry out strengthening measures on existing timber beams. When timber concrete composite (TCC) ceilings cannot be used, it is possible to reinforce the undersides of the [...] Read more.

In the case of load increases and the refurbishment of existing buildings, it is often necessary to carry out strengthening measures on existing timber beams. When timber concrete composite (TCC) ceilings cannot be used, it is possible to reinforce the undersides of the beams with structural steel or fiber composites (aramid or carbon-fiber-reinforced polymer). This work investigates how significant effects on the load-bearing and deformation behavior can be achieved with these materials in terms of construction practice. The article is intended to show structural engineers which reinforcement measures lead to which forces, deformations, etc., and how these are utilized. This should form the basis for the planning of reinforcement measures, as it is not clear from the beginning whether AFRP, CFRP, or steel is the most suitable material. For this purpose, a comparative parameter study was carried out under practical conditions and with a variable degree of reinforcement using the corresponding formulas. The internal forces in the timber and reinforcement cross-sections, the deflection behavior, and the failure loads at the strength and design levels were calculated. It was demonstrated that, particularly for steel and carbon-fiber-reinforced polymer (CFRP) reinforcements, significant increases in the ultimate load can be achieved and the often-important deformation behavior can be significantly improved. Especially the steel variant leads to high improvements in deflection and breaking load behavior, with the base material (wood) also being utilized more economically as a result. A comparative ecological study in the form of the global warming potential showed that reinforcement methods are also advantageous from the point of view of sustainability compared to renovations with timber concrete composite slabs or new concrete slabs. Full article

(This article belongs to the Section Advanced Composites)

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18 pages, 8668 KiB

Open AccessArticle

The Preparation and Properties of Ultra-High-Performance Concrete with Aeolian Sand: A Lab Study on the Effect of the Curing Method

by Yang Lv, Boyu Zhao, Jie Zhu, Chenhao He, Yunlu Ge, Yuanshuai Wu, Yanchao Zhu, Jianming Dan, Yang Zhou and Xiangguo Li

Materials 2025, 18(9), 2031; https://doi.org/10.3390/ma18092031 - 29 Apr 2025

Abstract

The utilization of aeolian sand (AS) as a substitute for river sand (RS) in ultra-high-performance concrete (UHPC) offers a sustainable solution to address natural sand resource shortages while enhancing AS utilization. This study systematically evaluates the influence of AS content (0–100% RS replacement [...] Read more.

The utilization of aeolian sand (AS) as a substitute for river sand (RS) in ultra-high-performance concrete (UHPC) offers a sustainable solution to address natural sand resource shortages while enhancing AS utilization. This study systematically evaluates the influence of AS content (0–100% RS replacement by mass) on the workability, mechanical properties, and microstructure of UHPC under different curing regimes. All mixtures incorporate 0.65% by volume of straight steel fibers to ensure adequate fiber reinforcement. The results reveal that the spherical morphology, smooth surface nature, and fine particle size of AS enhance the matrix fluidity and reduce the early autogenous shrinkage of UHPC. By employing steam curing at 90 °C for 2 d followed by standard curing for 7 d (M3), UHPC samples with a 60% and 80% AS substitution achieve a compressive strength of 132.4 MPa and 130.8 MPa, respectively; a flexural strength exceeding 18 MPa; a porosity below 10%; and a gel pore content exceeding 60%. The steel fiber reinforcement contributes significantly to the flexural performance, with the fiber–matrix interface quality maintained even at high AS replacement levels. These findings highlight the feasibility of AS as an alternative fine aggregate in UHPC. Full article

(This article belongs to the Special Issue Sustainability in Asphalt, Concrete and Pavement Materials: Design, Performance, and Characterization)

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11 pages, 3775 KiB

Open AccessArticle

Deformation Behavior of S32750 Duplex Stainless Steel Based on In Situ EBSD Technology

by Shun Bao, Han Feng, Zhigang Song, Jianguo He, Xiaohan Wu and Yang Gu

Materials 2025, 18(9), 2030; https://doi.org/10.3390/ma18092030 - 29 Apr 2025

Abstract

In this study, we investigated the two-phase hardening behavior and microstructural evolution of S32750 duplex stainless steel during the tensile deformation process. The analysis was conducted using in situ electron backscatter diffraction (EBSD), scanning electron microscopy (SEM), and microhardness testing. It was observed [...] Read more.

In this study, we investigated the two-phase hardening behavior and microstructural evolution of S32750 duplex stainless steel during the tensile deformation process. The analysis was conducted using in situ electron backscatter diffraction (EBSD), scanning electron microscopy (SEM), and microhardness testing. It was observed that strain transfer occurred between the two phases in the position away from the fracture. The ferrite phase exhibited softening, while the austenite phase underwent hardening. In the region less than 1 mm from the fracture site, both phases experienced a rapid hardening, with the maximum hardness difference between the two phases near the fracture reaching approximately 45 HV. In situ EBSD results indicate that the kernel average misorientation (KAM) value for the ferrite phase consistently exceeds that of the austenite phase during the initial stages of deformation. Conversely, in the final stages of deformation, the KAM value for austenite surpasses that of ferrite. In the initial stage of deformation, the type of grain boundaries in both phases remains largely unaltered. However, in the later stages of deformation, there is a marked increase in the number of small-angle grain boundaries within ferrite, which become approximately three times that of the large-angle grain boundaries. As deformation progresses, the maximum orientation distribution density of the ferrite phase is reduced by approximately 50%, with the preferred orientation shifting from the {100} plane to the {111} plane. In contrast, the orientation distribution of the austenite remains relatively uniform, with no significant change in the maximum orientation distribution density observed. This indicates that after substantial deformation, the rotation of ferrite grains significantly increases the deformation resistance, whereas the austenite phase continues to harden. This differential behavior leads to the continuous accumulation of strain at the phase boundaries, ultimately causing cracks to form at these boundaries and resulting in the sample’s fracture. Full article

(This article belongs to the Special Issue From Materials to Applications: High-Performance Steel Structures)

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13 pages, 5193 KiB

Open AccessArticle

Deep-Subwavelength Composite Metamaterial Unit for Concurrent Ventilation and Broadband Acoustic Insulation

by Xiaodong Zhang, Jinhong He, Jing Nie, Yang Liu, Huiyong Yu, Qi Chen and Jianxing Yang

Materials 2025, 18(9), 2029; https://doi.org/10.3390/ma18092029 - 29 Apr 2025

Abstract

Balancing ventilation and broadband sound insulation remains a significant challenge in noise control engineering, particularly when simultaneous airflow and broadband noise reduction are required. Conventional porous absorbers and membrane-type metamaterials remain fundamentally constrained by ventilation-blocking configurations or narrow operational bandwidths. This study presents [...] Read more.

Balancing ventilation and broadband sound insulation remains a significant challenge in noise control engineering, particularly when simultaneous airflow and broadband noise reduction are required. Conventional porous absorbers and membrane-type metamaterials remain fundamentally constrained by ventilation-blocking configurations or narrow operational bandwidths. This study presents a ventilated composite metamaterial unit (VCMU) co-integrating optimized labyrinth channels and the Helmholtz resonators within a single-plane architecture. This design achieves exceptional ventilation efficiency through a central flow channel while maintaining sub-λ/30 thickness (λ/31 at 860 Hz). Coupled transfer matrix modeling and finite-element simulations reveal that Fano–Helmholtz resonance mechanisms synergistically generate broadband transmission loss (STL) spanning 860–1634 Hz, with six STL peaks in the 860 and 1634 Hz bands (mean 18.4 dB). Experimental validation via impedance tube testing confirmed excellent agreement with theoretical and simulation results. The geometric scalability allows customizable acoustic bandgaps through parametric control. This work provides a promising solution for integrated ventilation and noise reduction, with potential applications in building ventilation systems, industrial pipelines, and other noise-sensitive environments. Full article

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14 pages, 9327 KiB

Open AccessArticle

Evaluation of Crack Formation in Heat Pipe-Welded Joints

by Min Ji Song, Keun Hyung Lee, Jun-Seob Lee, Heesan Kim, Woo Cheol Kim and Soo Yeol Lee

Materials 2025, 18(9), 2028; https://doi.org/10.3390/ma18092028 - 29 Apr 2025

Abstract

This study investigates the failure of a 750A dual-insulated pipeline, where cracks developed along the weld joints during heat supply resumption at the district heating facility. A comprehensive analysis was conducted through visual inspection, mechanical testing, microstructural characterization, finite element analysis (FEA), and [...] Read more.

This study investigates the failure of a 750A dual-insulated pipeline, where cracks developed along the weld joints during heat supply resumption at the district heating facility. A comprehensive analysis was conducted through visual inspection, mechanical testing, microstructural characterization, finite element analysis (FEA), and electrochemical corrosion testing. The results indicate that cracks were generated in the heat-affected zone (HAZ), primarily caused by galvanic corrosion and thermal expansion-induced stress accumulation. Open circuit potential (OCP) measurements in a 3 M NaCl solution confirmed that the HAZ was anodic, leading to the most vulnerable position to corrosion. Furthermore, localized electrochemical tests were conducted for respective microstructural regions within the HAZ. The results reveal that coarse-grained HAZ exhibited the lowest corrosion potential, giving rise to preferential corrosion, promoting pit formation, and serving as initiation sites for stress concentration and crack propagation. FEA simulations demonstrate that pre-existing microvoids in the HAZ act as stress concentration sites, undergoing a localized stress exceeding 475 MPa. These findings emphasize the importance of controlling microstructural stability and mechanical integrity in welded pipelines, particularly in corrosive environments subjected to thermal stresses. Full article

(This article belongs to the Special Issue Corrosion Behavior and Mechanical Properties of Metallic Materials (Second Edition))

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20 pages, 8770 KiB

Open AccessArticle

Failure and Energy Evolution Characteristics of Saturated Natural Defective Material Under Different Confining Pressures

by Zhihao Gao, Shihao Guo, Xiaoyong Yang, Shanchao Hu, Junhong Huang, Yafei Cheng, Dawang Yin and Jinhao Dou

Materials 2025, 18(9), 2027; https://doi.org/10.3390/ma18092027 - 29 Apr 2025

Abstract

In nature, many brittle materials contain natural defects such as microcracks or joints, for example, rocks. Under water-saturated conditions, the strength of defective materials undergoes varying degrees of attenuation, leading to material failure and even structural instability in engineering contexts. Moreover, the deformation [...] Read more.

In nature, many brittle materials contain natural defects such as microcracks or joints, for example, rocks. Under water-saturated conditions, the strength of defective materials undergoes varying degrees of attenuation, leading to material failure and even structural instability in engineering contexts. Moreover, the deformation and failure of defective brittle materials are essentially the result of the accumulation and dissipation of energy. Studying the energy evolution of defective brittle materials under load is more conducive to reflecting the intrinsic characteristics of strength changes and overall failure of brittle materials under external loading. Natural defective brittle rock materials were firstly water saturated and triaxial compression tests were performed to determine the mechanical properties of water-saturated materials. The energy evolution patterns of water-saturated materials under varying confining pressures were also obtained. Using the discrete element method, the macro- and micro-failure characteristics of water-saturated materials were investigated, revealing the mesoscopic mechanisms of deformation and failure evolution in these materials. The results indicate that confining pressure significantly enhances the peak compressive strength and elastic modulus of water-saturated defective materials. When the confining pressure increased from 0 MPa to 20 MPa, the peak strength and elastic modulus of the water-saturated materials increased by 126.8% and 91.9%, respectively. Confining pressure restricts the radial deformation of water-saturated materials and dominates the failure mode. As confining pressure increases, the failure mode transitions from tensile splitting (at 0 MPa confining pressure) to shear failure (at confining pressures ≥ 10 MPa), with the failure plane angle gradually decreasing as confining pressure rises. Confining pressure significantly alters the energy storage–release mechanism of water-saturated defective brittle materials. At peak load, the total energy, elastic energy, and dissipated energy increased by 347%, 321%, and 1028%, respectively. The ratio of elastic energy storage to peak strain ratio shows a positive correlation, and the elastic storage ratio of water-saturated defective brittle materials under confining pressure is always higher than that without confining pressure. When the strain ratio exceeds 0.94, a negative correlation between confining pressure and the rate of elastic storage ratio is observed. From the perspective of mesoscopic fracture evolution in water-saturated defective brittle materials, the crack propagation path shifts from the periphery to the center of the material, and the fracture angle decreases linearly from 89° to 58° as confining pressure increases. The dominant direction of crack development is concentrated within the 45–135° range. The findings elucidate the mechanisms by which water saturation and confining pressure influence the strength degradation of natural defective brittle materials from both mesoscopic and energy perspectives, providing theoretical support for the stability control of related engineering structures. Full article

(This article belongs to the Special Issue Advances in Material Structural Analysis: Finite Element Analysis and Numerical Modelling)

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14 pages, 9589 KiB

Open AccessArticle

Evolutions in Microstructure and Mechanical Properties of Ultra-Thin Oligocrystalline Invar Alloy Strip During Cold Rolling

by Jianguo Yang, Yajin Xia, Qingke Zhang, Genbao Chen, Cheng Xu, Zhenlun Song and Jiqiang Chen

Materials 2025, 18(9), 2026; https://doi.org/10.3390/ma18092026 - 29 Apr 2025

Abstract

The ultra-thin Invar alloy strips are widely used in the manufacture of the fine masks; cold rolling of such thin strips (<100 μm) poses significant difficulties, primarily due to the limited number of grains within the thickness range. Consequently, it is important to [...] Read more.

The ultra-thin Invar alloy strips are widely used in the manufacture of the fine masks; cold rolling of such thin strips (<100 μm) poses significant difficulties, primarily due to the limited number of grains within the thickness range. Consequently, it is important to understand the grain structure and property evolutions of the ultra-thin Invar alloy strips during cold rolling. In this study, an annealed Invar36 alloy strip, 100 µm thick, was cold rolled to different thicknesses, and the surface deformation morphologies, cross-sectional grain structure, intracrystalline microstructure and tensile properties of these thin strips were characterized and analyzed. The results show that plastic deformation of the initial annealed equiaxed grains is not uniform, depending on the grain orientation, resulting in different slip bands morphologies, unevenness and increase in roughness. Meanwhile, the grain rotation and rolling texture develop with increasing cold rolling reduction. The dislocation density in the 60% cold-rolled strip is about decuple that of the original annealed strip, and high-density tangled dislocations are formed, making the tensile strength increase from 430 MPa to 738 MPa. Grain refining and proper intermediate annealing are proposed to optimize the thickness uniformity, evenness and surface roughness. Full article

(This article belongs to the Special Issue Forming Technologies and Mechanical Properties of Advanced Materials - 2nd Volume)

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21 pages, 27535 KiB

Open AccessArticle

A Comparative Study of A₂SiF₆ (A = Cs, K) Phosphor Host Matrices: Linear Combination of Atomic Orbital Hybrid Density Functional Theory Calculations

by Leonid L. Rusevich, Mikhail G. Brik, Denis Gryaznov, Alok M. Srivastava, Ilya D. Chervyakov, Guntars Zvejnieks, Dmitry Bocharov and Eugene A. Kotomin

Materials 2025, 18(9), 2025; https://doi.org/10.3390/ma18092025 - 29 Apr 2025

Abstract

Cesium hexafluorosilicate (Cs₂SiF₆, CSF) and potassium hexafluorosilicate (K₂SiF₆, KSF) compounds are suitable hosts for luminescent impurities. In this work, the results of first-principle calculations of the basic properties of both these compounds are discussed and [...] Read more.

Cesium hexafluorosilicate (Cs₂SiF₆, CSF) and potassium hexafluorosilicate (K₂SiF₆, KSF) compounds are suitable hosts for luminescent impurities. In this work, the results of first-principle calculations of the basic properties of both these compounds are discussed and compared with the available experimental and theoretical data. The simulations were performed using the CRYSTAL23 computer code within the linear combination of atomic orbitals (LCAO) method of the density functional theory (DFT) and the advanced hybrid DFT-HF exchange-correlation B1WC functional. A comparative study of the structural, electronic, and elastic properties of the two materials is presented, along with a study of the dependence of properties on external pressure in the range of 0–20 GPa. In particular, the electronic properties with an emphasis on the effective atomic charges (by means of Mulliken analysis) and the chemical bonding properties (by means of crystal orbital overlap population (COOP) analysis) were addressed, with regards to the pressure effects. The structure of the valence bands at 0 and 20 GPa was compared. The vibrational properties of CSF and KSF were calculated, including the simulation of the one-phonon IR and Raman spectra. The calculated Raman spectra exhibit excellent agreement with the experimental ones. The pressure dependences of sound speeds and the Debye temperature are evaluated. Full article

(This article belongs to the Section Materials Simulation and Design)

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