High Temperature Performance Research Articles

Integrated approach for improving mechanical and high-temperature properties of fast-growing poplar wood using lignin-controlled treatment combined with densification

Previous studies on the modification of fast-growing wood have extensively examined the effects of density and lignin content on the strength and high-temperature properties of modified wood. However, a comprehensive quantitative analysis of their effects on high-temperature performance remains insufficient. To address this knowledge gap, we applied alkali treatment and compression densification to fast-growing poplar, resulting in modified specimens with varying densities and lignin levels. The quantitative effects of density and lignin content on high-temperature properties were meticulously evaluated. Chemical changes were analyzed using Fourier transform infrared spectroscopy (FT-IR), while the mechanical and high-temperature properties were comprehensively assessed. Delignification was found to be positively correlated with treatment duration, with hemicellulose degradation also detected via FT-IR analysis. Significant enhancements were recorded in flexural strength, tensile strength, and modulus of elasticity, accompanied by improvements in ductility ratio and compressive strength. The modified poplar wood exhibited increased thermal stability at elevated temperatures. Furthermore, density and lignin content were identified as significant factors affecting high-temperature performance, establishing minimum density thresholds for various lignin contents in modified poplar wood to ensure optimal performance. This study enhances to the understanding of the intricate relationships among wood properties, modification techniques, and high-temperature performance.

Effects of Laboratory Ageing on the Chemical Composition and High-Temperature Performance of Warm Mix Asphalt Binders

Warm asphalt mixtures can suffer from decreased short-term high-temperature performance; therefore, introducing additional modifiers can mitigate this risk. This study investigates the effects of a liquid organosilane warm mix additive (WMAd) and grade-bumping polyethylene-based additive added simultaneously to asphalt binders on their chemical composition and its relationship with performance characteristics. Previous studies found relationships between the formation of certain chemical species during bitumen ageing and the increase in their viscosity, stiffness and other performance characteristics—the present work intended to verify these relationships when the two mentioned additives are used. Two asphalt binders were investigated—a paving-grade 50/70 binder and a 45/80-55 polymer-modified bitumen. The chemical analysis was performed using Fourier-transform infrared (FTIR) spectroscopy in attenuated total reflectance mode and focused on the quantification of carbonyl, sulfoxide, polybutadiene and polystyrene structures in the asphalt binders subjected to laboratory short- and long-term ageing. Additionally, the relationships between asphalt binder performance and selected FTIR indices were evaluated using a dynamic shear rheometer. It was found that the investigated additives significantly affected the apparent contents of all evaluated chemical structures in the asphalt binders; however, these changes were not reflected in their performance evaluation.

Microstructure evolution and mechanical properties of bioinspired interpenetrating Ti2AlNb/TiAl matrix composite with a crossed-lamellar structure

TiAl alloys with low density, high creep resistance and high temperature performance are considered as candidate materials to replace nickel-based superalloys in the range of 700∼800 °C. However, the intrinsic brittleness of TiAl alloys has always been the biggest bottleneck restricting their development. In this paper, a bioinspired interpenetrating Ti2AlNb/TiAl composite with crossed-lamellar structure was prepared by combining selective laser melting (SLM) and vacuum hot press sintering (HPS) under the condition of 1150 °C/1 h/45 MPa, to improve the strength and toughness of the composite. Meanwhile, the metallurgical defects and microstructure of Ti2AlNb reinforcement skeleton printed under different volume energy densities (VEDs) were investigated, as well as the evolution of the microstructure at the interface region of the composite was systematically studied. What's more, we studied the mechanical properties of the composite including nanoindentation test, room temperature tensile and bending tests. The results show that the VED is 88.89 J/mm3, an almost completely dense reinforcement skeleton (∼99.8 %) is obtained. The interface region can be divided into four different reaction layers, namely LⅠ, LⅡ, LⅢ and LⅣ, due to the diffusion of elements. LⅠ is mainly composed of Othick/thin lath-like phase and O short rod-like phase. LⅡ is mainly composed of B2/β phase, acicular α2 phase and nanoscale ω-Ti3NbAl2 phase. The LⅢ mainly consists of B2/β phase. The LⅣ is composed of α2 phase. The deformability of each phase in the composite: B2/β phase > O phase >γ phase >α2 phase >ω phase. The tensile strength and fracture toughness of bioinspired interpenetrating Ti2AlNb/TiAl matrix composite are increased by 24.0 % and 89.0 %, respectively, compared with TiAl alloy, which is mainly contributed to the strong interfacial bonding between matrix and reinforcement as well as the synergistic effect of Ti2AlNb reinforcement with high strength and toughness.

Sewage sludge ash as filler in asphalt mastic: Low-temperature towards high-temperature performance

The sewage sludge ash (SSA) is characterized as a by-product used in the pavement industry to mitigate the environmental risks, enhance the landfill capacity and conserve the non-renewable resources. This research utilized SSA as a filler substitute in asphalt mastic, and its performance-based properties from low towards high temperatures were evaluated. For this goal, the physical and chemical properties of SSA and rock powder (used as base filler) were determined using BET surface area measurement, X-ray fluorescence, and scanning electron microscopy tests. The performance of base and SSA-modified asphalt mastics in four filler/bitumen weight ratios (0.6, 0.8, 1, and 1.2) was investigated using dynamic shear rheometer, multiple stress creep and recovery, linear amplitude sweep, and bending beam rheometer tests across a wide temperature range. The results indicate that SSA has a higher specific surface area, better bitumen absorption, and lower density compared to the base filler. Additionally, unlike the acidic nature of the base filler, SSA possesses strong basic properties, leading to a stronger chemical bond with bitumen and enhanced resistance to aging, particularly at high temperatures. Moreover, the lower density of SSA escalates the amount of filler per unit volume of the SSA-modified asphalt mastic, leading to the increased stiffness and elasticity. This trend improves resistance to permanent deformation and cracking at medium temperatures, although it has an adverse effect on performance of mastic at low temperatures. Moreover, due to the improved performance of SSA-modified asphalt mastic, this study can contribute to the sustainable development of the pavement industry.

Research progress on high-temperature properties of carbon fiber reinforced polymer composites for cables

Carbon fiber reinforced polymer composites (CFRP) cable has advantages of lightweight, high strength, and excellent durability, providing a new materials for cables and bringing out potential breakthrough in spanning capacity of structures. At present, CFRP cable has already been applied in some engineering bridges. The fire resistance performance of CFRP cable is critical for ensuring structure safety when suffering accidental fire disaster, and clarifying mechanical performance deterioration and failure mechanism of CFRP cable at elevated temperature is fundamental for research of its fire resistance. This paper summarizes current research progress on high-temperature properties of CFRP cable from two levels, including epoxy resin matrix and CFRP composites. Firstly, at resin matrix level, mechanical properties of epoxy resin and its degradation at elevated temperatures are reviewed and analysed, and potential ways to improve high-temperature performance of epoxy resin are suggested. Secondly, at CFRP composites level, high-temperature properties test methods and mechanical performance of CFRP composites in longitudinal direction and transverse direction at elevated temperatures are summarized and discussed. In addition, research shortage of high-temperature properties of CFRP cable is summarized, and corresponding further research is recommended.

Enhanced high-temperature performance of selected high-entropy rare earth disilicates

First-principles calculations were utilized to evaluate the synthesis feasibility of (Yb0.2Y0.2Lu0.2Ho0.2Er0.2)2Si2O7, (Yb0.2Tm0.2Lu0.2Sc0.2Er0.2)2Si2O7, (Yb0.2Tm0.2Lu0.2Sc0.2Gd0.2)2Si2O7, and (Yb0.2Y0.2Lu0.2Sc0.2Gd0.2)2Si2O7, followed by their fabrication using the solid-phase reaction method. This study investigates the thermal properties of four novel high-entropy rare earth disilicates and compares them with Yb2Si2O7, a material known for its high-temperature stability. The aim was to explore the influence of high configurational entropy and small grain size on enhancing material properties that are critical in high-temperature applications. Key findings demonstrated that these high-entropy materials exhibit lower thermal conductivity, higher specific heat capacity, an0d reduced coefficient of thermal expansion compared to Yb2Si2O7. Among them, (Yb0.2Tm0.2Lu0.2Sc0.2Er0.2)2Si2O7 and (Yb0.2Y0.2Lu0.2Ho0.2Er0.2)2Si2O7 have the lowest thermal conductivity and suitable CTE, making them the best choices for advanced thermal/environmental barrier coatings in high-temperature applications. Furthermore, the in-depth discussion in this study provides guidance for designing high-entropy rare earth disilicate materials with ideal CTE and thermal insulation properties.

A review on recent progress of refractory high entropy alloys: From fundamental research to engineering applications

Refractory high-entropy alloys (RHEAs) have emerged as frontier materials for high-temperature structural applications due to their exceptional mechanical properties and thermal stability. This review aims to provide a comprehensive and in-depth summary of the latest research progress in the field of RHEAs. By systematically analyzing 253 publications since 2022, this review presents a panoramic overview of the current research status in the field of RHEAs, covering aspects from alloy design, microstructure, processing techniques, mechanical behavior, to physicochemical properties. Key strengthening and toughening mechanisms, such as solid solution strengthening, precipitation strengthening, and grain boundary strengthening, are extensively analyzed. The high-temperature mechanical performance, oxidation resistance, and adaptability of RHEAs in extreme environments including corrosion and irradiation, are critically reviewed, and the potential application value of these research findings in aerospace, nuclear energy, biomedical, and other fields is discussed. Simultaneously, the multidisciplinary characteristics of RHEAs research has revealed the trend of the field evolving from fundamental research to practical applications. Furthermore, with the aid of advanced characterization techniques and computational methods, the review elucidates the controlling effects of chemical short-range order, defect structures, and other factors on the performance evolution of RHEAs, highlighting the importance of multi-principal element synergistic effects. Based on summarizing the key scientific issues and technological bottlenecks faced by RHEAs, the article provides a forward-looking perspective on future research directions, emphasizing development strategies that integrate computation and experiments, and accelerate the transformation of fundamental research into engineering applications, thus providing insights and guidance for developing a new generation of high-performance RHEAs.

Effect of fast charging on degradation and safety characteristics of lithium-ion batteries with LiFePO4 cathodes

Fast charging compatibility is a desirable feature for batteries to shape a promising future in our rechargeable world. Enabling fast charging of advanced energy-dense Li-ion batteries for growing electric vehicle (EV) markets depends on the breakthrough of material chemistry and optimization of charging strategy. Lithium iron phosphate (LiFePO4, or LFP) is a pivotal cathode material in state-of-the-art EV batteries due to the merits of high thermal stability, long cycle lifetime, and high-temperature performance. However, degradation-safety interactions of LFP-based Li-ion batteries under fast charging conditions and low temperatures remain elusive. In this study, we cycle LFP cells under different fast charging strategies and thermal environments to understand their effects on degradation pathways, where the capacity, voltage, temperature, coulombic inefficiency, internal resistance, and impedance spectroscopy are evaluated. Half-cell studies are implemented to assess electrode-level capacity retentions. Post-mortem analyses are conducted to reveal physicochemical changes in electrodes. Accelerating rate calorimeter tests are carried out to measure evolutions of cell-level thermal instabilities after fast charging tests. This research article highlights the significant roles of graphite-centric lithium plating and LFP-centric transition metal dissolution in driving substantial electrochemical degradations, suggesting that a mild low temperature does not necessarily reduce the LFP cell lifetime.

Deformation behavior of PST-TiAl bicrystals at 800 °C

PST (polysynthetic twinned) TiAl crystal exhibits excellent mechanical properties, and thus, it has been regarded as a critical candidate for turbine blades in the aero-engine industry. For the first time, the deformation behavior of PST-TiAl bicrystals with two different α2/γ lamellar orientations was studied in this work. Ti-46Al-6Nb bicrystals were cut from directionally solidified ingots, and three bicrystals of B1 (10°–14°), B2 (10°–19°), B3 (6°–75°) together with a single crystal of S1 (3°) were stretched at 800 °C. Then, the deformation behaviors, including fracture morphology, crack propagation, and deformation mechanism, were analyzed. Interestingly, these bicrystals show good high-temperature tensile performance, and their deformation behaviors seem to be very anisotropic. The findings indicate that the misorientation disparity in bicrystals primarily determines their deformation coordination capacity and corresponding mechanical performance. Subsequently, the difference in deformation orientation between the two lamellae significantly controls fracture behavior and deformation compatibility. High slip potential and abundant variant choices in γ phases are supposed to be beneficial for deformation capacity improvement. Meanwhile, the deformation potential of ordinary dislocation and superlattice dislocation slip systems in the α2 phase was also examined. Results show that the disparity in dislocation motion ability between γ variants gradually amplifies the advantages of the easy-mode phase in deformation through strain coordination, while mitigating the disadvantages associated with the difficult-mode phase. During further deformation, the relatively low bicrystal misorientation and small deformation capacity differences between the two lamellae determine high deformation coordination and improved performance. Overall, our work reveals that bicrystal deformation initiates at the relatively softer lamellae and proceeds to the harder lamellae, and its final comprehensive performance is determined by the deformation coordination capacity between the two lamellae.

Enhanced High-Temperature Thermoelectric Performance in Te-Doped Electronegative Element-Filled Skutterudites via Suppressing Bipolar Effects and Enhanced Phonon Scattering.

CoSb3-based skutterudites have great potential as midtemperature thermoelectric (TE) materials due to their low cost and excellent electrical and mechanical properties. Their application, however, is limited by the high thermal conductivity and the degradation of TE performance at elevated temperatures, attributed to the adverse effects of bipolar diffusion. Herein, a series of SeyCo4Sb12-xTex compounds were successfully synthesized by combining a solid-state reaction and spark plasma sintering techniques to mitigate these challenges. It was found that doping Te at the Sb sites effectively enhanced the carrier concentration and suppressed the bipolar effect to obtain a superior power factor of ∼43 μW cm-1 K-2. Furthermore, due to the low resonant frequency of Se, filling voids of CoSb3 with Se achieved a low lattice thermal conductivity of 1.55 W m-1 K-1. Nevertheless, Se filling introduced additional holes, reducing the carrier concentration without a significant detriment of the carrier mobility. As a result, a maximum figure of merit of 1.23 was achieved for Se0.1Co4Sb11.55Te0.45 at 773 K. This work provides a valuable guidance for selecting appropriate filling and doping components to achieve synergistic optimization of the acoustics and electronics of CoSb3-based skutterudites.

Enhancing the activity and sulfur resistance of CuFeAlOx catalyst via the structure effect for the simultaneous removal of Hg0 and NO at wide temperature

The efficient strategy for improving SO2 resistance and catalytic activity is structural modification. Herein, the CuFeAlOx catalysts with different structures, including one-dimensionally disordered mesoporous nanoparticles structure (CuFeAl-N), one-dimensionally ordered mesoporous nanoparticles structure (CuFeAl-C), three-dimensionally ordered porous honeycomb-like structure (CuFeAl-P) and three-dimensionally ordered porous flower-like structures (CuFeAl-CP), were synthesized via a template method to investigate structure effect on activity and sulfur resistance of the catalyst for simultaneously removing NO and Hg0 at wide temperature. The results showed that the various surface characteristics resulted in distinct behaviours with regards to SO2 tolerance. CuFeAl-CP and CuFeAl-C exhibits excellent SO2 resistance, but CuFeAl-N catalyst presents poor SO2 resistance. The CuFeAl-CP with the flower-like structure possesses large specific surface area, which can expose more active sites and exhibited highly dispersed active component. More importantly, it reacts with SO2 to generate reactive sulfate providing additional acid sites, which significantly promotes high-temperature catalytic performance. One-dimensionally ordered mesoporous and three-dimensionally ordered porous effectively facilitates mass transfer of reactants and ammonium sulphate decomposition, thereby inhibiting surface sulfation and ammonium sulfate species deposition. This work lays the foundation for developing highly efficient SCR catalysts that are tolerant to SO2.

A comparative study into the effect of spent coffee powder and ash on improving the mechanical properties of bitumen

Nowadays, waste and renewable materials are used to modify bitumen and asphalt, reduce costs, decrease the use of natural resources, and maintain ecological balance, and have thus received much attention. This study aimed to improve the rheological properties of bitumen and reduce spent coffee grounds' (SCG) waste by partially replacing it with SCG powder and ash. SCG powder and ash were added in percentages of 0, 1, 3, 5, and 8 wt percent of bitumen to check the properties of control and modified bitumens. Microstructural properties were evaluated by Fourier transform infrared spectroscopy, thermal gravimetric analysis, X-ray fluorescence spectroscopy (XRF), and scanning electron microscopy (SEM). Penetration, softening point, and ductility tests were performed to check the physical properties of bitumens, along with the storage stability test. Rheological tests (viscosity, bending beam rheometer (BBR), dynamic shear rheometer (DSR), multiple stress creep and recovery (MSCR), and linear amplitude sweep (LAS) were also carried out. According to the BBR results, adding SCG powder up to −12 °C and adding SCG ash up to −6 °C increased the resistance to low temperatures. Based on DSR and MSCR results, SCG, either in the form of ash or powder, increased the resistance to rutting, and adding SCG ash improved the high temperature performance of bitumen by 1 grade. At 64 °C, adding 8 % of SCG powder increased the rutting resistance by 43 %, and adding SCG ash raised the rutting resistance by about 113 %. LAS results also showed that SCG ash outperforms SCG powder in fatigue. Although both SCG powder and ash performed well in high, moderate, and low temperatures, SCG powder performed better in cold regions, and SCG ash performed better in regions with temperate and tropical climates.

Thermal Corrosion Properties of Composite Ceramic Coating Prepared by Multi-Arc Ion Plating

In this study, a NiCr/YSZ coating was applied to a γ-TiAl surface using multi-arc ion plating technology to enhance its high-temperature performance and explore the mechanisms of high-temperature oxidation and thermal corrosion. The thermal corrosion properties of the γ-TiAl matrix and NiCr/YSZ coating were investigated at 850 °C and 950 °C using a constant-temperature corrosion test in a 75% Na2SO4 + 25% NaCl mixture. The results indicate that after 100 h, the thermal corrosion weight gain of the coating samples was 70.1 mg/cm2 at 850 °C and 118.2 mg/cm2 at 950 °C. At these temperatures, sulfide formation on the surface increases, leading to a loose and porous surface. After 100 h of high-temperature corrosion at 850 °C, the primary oxidation product on the surface of the coating was tetragonal-ZrO2. At 950 °C, Y2O3, which mainly acts as a stabilizer in YSZ, reacted with Na2SO4, resulting in the continuous consumption of Y2O3. This reaction caused a substantial amount of tetragonal-ZrO2 to transform into monoclinic-ZrO2, altering the volume of the ceramic layer, which induced internal stress, crack propagation, and minor spallation. A continuous and dense internal thermally grown oxide (TGO) layer effectively impeded the diffusion of molten salt substances and oxygen, thereby significantly improving the thermal corrosion resistance of the thermal barrier coating.

AUBERT & DUVAL PER72

Abstract Aubert and Duval PER72 (NiCr18Co15TiMoAI alloy) is a precipitation hardening, nickel-base superalloy. The alloy is solid solution strengthened by additions of chromium, cobalt, molybdenum, and tungsten, while additions of titanium and aluminum provide precipitation strengthening. Aubert & Duval PER72 combines high strength with metallurgical stability as demonstrated by excellent impact strength retention after long exposures at elevated temperatures. It also exhibits good oxidation resistance, as well as excellent resistance to sulfide corrosion. This datasheet provides information on composition, physical properties, elasticity, and tensile properties. It also includes information on low temperature performance, high temperature performance, and corrosion resistance as well as forming and heat treating. Filing Code: Ni-787. Producer or source: Aubert & Duval S.A. (a member of the Eramet Group).

SAE 1012, JIS S12C

Abstract 1012 and S12C are wrought low-carbon (carbon = 0.10–0.15 percent) non-alloy steels that are used in the as rolled, annealed, normalized, or cold worked condition. These steels are characterized by low strength, high ductility, excellent cold formability, and excellent weldability. Within the carbon range of these steel grades, strength and hardness will increase with increase in carbon content and with cold work. Such increases in strength are at the sacrifice of ductility or the ability to withstand cold deformation. Grades 1012 and S12C are widely used for lightly stressed parts that require higher strength levels than can be achieved by the lower carbon grades and for applications where cold formability is the primary requisite. They are less expensive than 1008 and can be used when the requirements for cold forming are less exacting. 1012 and S12C may also be used in the case hardened, nitrided, or nitrocarburized condition. This datasheet provides information on composition, physical properties, microstructure, hardness, and tensile properties. It also includes information on low and high temperature performance as well as forming and heat treating. Filing Code: CS-268. Producer or source: Heat Treater's Guide.

Synergistic effects of buton rock asphalt and BBOEA on the enhanced temperature resistance and flexibility of asphalt

To improve the toughness of transportation infrastructure and develop asphalt composite materials with both elasticity and toughness, this paper prepared Buton rock asphalt (BRA)/Bis[2-(2-butoxyethoxy)ethyl] adipate BBOEA composite modified asphalt. The evolution of high and low-temperature performance of the composite modified asphalt was explored through key asphalt indicators, dynamic shear rheology, and bending beam rheometer (BBR) tests. The performance improvement mechanism of the asphalt was investigated using Fourier transform infrared spectroscopy (FTIR). The addition of Buton rock asphalt effectively improved the high-temperature performance of the asphalt, raising the high-temperature PG grade from 64 to 70 and enhancing resistance to permanent deformation. The inclusion of 1.5 % BBOEA further enhanced low-temperature performance, reducing the stiffness modulus of BRA modified asphalt from 365 MPa to 260 MPa, a decrease of 26.9 %. This improvement is attributed to the polar adipate functional groups in BBOEA, which promote hydrogen bonding and dipole–dipole interactions with polar groups in the resins, reducing micelle size and asphalt rigidity. With the high-temperature performance remaining robust and low-temperature flexibility and strain relaxation greatly improved, the optimal BBOEA content is recommended at 1.5 % of the asphalt mass.

First Principles Calculation of the Effect of Cu Doping on the Mechanical and Thermodynamic Properties of Au-2.0Ni Solder.

To meet the demands for high-temperature performance and lightweight materials in aerospace engineering, the Au-Ni solder is often utilized for joining dissimilar materials, such as Ti3Al-based alloys and Ni-based high-temperature alloys. However, the interaction between Ti and Ni can lead to the formation of brittle phases, like Ti2Ni, TiNi, and TiNi3, which diminish the mechanical properties of the joint and increase the risk of crack formation during the welding process. Cu doping has been shown to enhance the mechanical properties and high-temperature stability of the Au-Ni brazed joint's central area. Due to the difficulty in accurately controlling the solid solution content of Cu in the Au-Ni alloy, along with the high cost of Au, traditional experimental trial-and-error methods are insufficient for the development of Au-based solders. In this study, first principles calculations based on density functional theory were employed to analyze the effect of Cu content on the stability of the Au-2.0Ni-xCu (x = 0, 0.25, 0.5, 0.75, 1.0, 1.25 wt%) alloy phase structure. The thermal properties of the alloy were determined using Gibbs software fitting. The results indicate that the Au-2.0Ni-0.25Cu alloy exhibits the highest plastic toughness (B/G = 5.601, ν = 0.416, Cauchy pressure = 73.676 GPa) and a hardness of 1.17 GPa, which is 80% higher than that of Au-2.0Ni. This alloy balances excellent strength and plastic toughness, meeting the mechanical performance requirements of brazed joints. The constant pressure specific heat capacity (Cp) of the Au-2.0Ni-xCu alloy is higher than that of Au-2.0Ni and increases with Cu content. At 1000 K, the Cp of the Au-2.0Ni-0.25Cu alloy is 35.606 J·mol-1·K-1, which is 5.88% higher than that of Au-2.0Ni. The higher Cp contributes to enhanced high-temperature stability. Moreover, the linear expansion coefficient (CTE) of the Au-2.0Ni-0.25Cu alloy at 1000 K is 8.76 × 10-5·K-1, only 0.68% higher than Au-2.0Ni. The lower CTE helps to reduce the risk of solder damage caused by thermal stress. Therefore, the Au-2.0Ni-0.25Cu alloy is more suitable for brazing applications in high-temperature environments due to its excellent mechanical properties and thermal stability. This study provides a theoretical basis for the performance optimization and engineering application of the Au-2.0Ni-xCu alloy as a gold-based solder.

A single-phase Nb25Ti35V5Zr35 refractory high-entropy alloy with excellent strength-ductility synergy

Refractory high entropy alloys (RHEAs) are promising candidates for high-temperature structural materials due to their excellent high-temperature performance. However, the room-temperature brittleness of most alloys results in poor plastic formability, thereby limiting their engineering applications. In this study, Nb25Ti35V5Zr35 alloy with cold-rollability was developed, and its phase stability, tensile mechanical properties, elastic properties, strengthening mechanism, and deformation mechanism were investigated by combining experiments, CALPHAD, DFT and molecular statics (MS) methods. The results demonstrate that Nb25Ti35V5Zr35 alloy possesses good phase stability, with both the as-cast and annealed states maintaining a single-phase BCC structure without undergoing phase transformation. The tensile yield strength of the alloy reaches its peak at 1152 MPa in the cold-rolled condition, while its annealed state exhibits an optimal balance of strength and plasticity, with a yield strength of 836 MPa and an elongation of 22.45 %, respectively. Solid solution strengthening is the primary source of its high strength, with V and Zr playing key roles in this strengthening mechanism. Dislocation slip plays a dominant role in plastic deformation. Additionally, compared to traditional BCC alloys, the significance of edge dislocations in the deformation process is notably enhanced, with the {112} plane serving as the preferred slip plane for dislocations. DFT results indicate that the alloy exhibits significant anisotropy in both Young's modulus and shear modulus. This work contributes to understanding the material properties of the Nb25Ti35V5Zr35 alloy and provides a reference for the design of new ductile RHEAs.

Alter the charge transport orientation of aromatic polyimide by induction effect to achieve superior high-temperature capacitance performance

Aerospace, electric vehicles, and other particular application scenarios place higher demands on the applicable electric field and temperature of capacitors. Polyimide, as the most ideal and widely studied high-temperature capacitor dielectric material, has poor insulation performance under extreme conditions. The main reason is that many conjugated π-bonds on its aromatic rings provide channels for the movement of free electrons, this phenomenon is more intense in high-temperature and high-field environments, which accelerates the high-temperature performance degradation of polyimide. Herein, we propose a molecular structure strategy to design high-temperature capacitance performance polymer dielectrics based on the induction effect. Both the experimental and density functional theory calculation results indicate that the polar functional groups -CF3 and –OCH3 can lead to a strong induction effect, which changes the direction of electron transport on the aromatic ring, serve to weaken the free-sharing ability of electrons in the conjugated π bond, increases the energy levels of PI and induces the formation of local deep traps in the polymer films, which significantly restrains charge carrier transport, ultimately improves the high-temperature capacitance property for aromatic polyimide. The resultant polymer film exhibits an excellent discharged energy density (Ud) of 7.9 J/cm3 at 150 °C and 810.3 MV/m. Meanwhile, it maintains excellent stability at over 100,000 fatigue tests and 500 MV/m. Hopefully, it will provide theoretical and technical support for developing high-performance capacitors.

Oxidation Behavior of Lightweight Al0.2CrNbTiV High Entropy Alloy Coating Deposited by High-Speed Laser Cladding

High-temperature oxidation resistance is the major influence on the high-temperature service stability of refractory high entropy alloys. The oxidation behavior of lightweight Al0.2CrNbTiV refractory high entropy alloy coatings with different dilution ratios at 650 °C and 800 °C deposited by high-speed laser cladding was analyzed in this paper. The oxidation kinetic was analyzed, the oxidation resistance mechanism of the Al0.2CrNbTiV coating was clarified with the analysis of the formation and evolution of the oxidation layer, and the effect of the dilution rate on high-temperature performances was revealed. The results showed that the oxide layer was mainly composed of rutile oxides (Ti, Cr, Nb)O2 after isothermal oxidation at 650 °C and 800 °C for 50 h. The Al0.2CrNbTiV coating in low dilution exhibited better oxidation performance at 650 °C, due to the dense oxide layer formed with the synergistic growth of fine AlVO3 particles and (Ti, Cr, Nb)O2, and higher percentage of Cr, Nb in (Ti, Cr, Nb)O2 strengthened the lattice distortion effect to inhibit the penetration of oxygen. The oxide layer formed at 800 °C for the Al0.2CrNbTiV coating was relatively loose, but the oxidation performance of the coating in high dilution improved due to the precipitation of Cr2Nb-type Laves phases along grain boundaries, which inhibits the diffusion of oxygen.