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Poly (p-phenylene terephthalamide) (PPTA), is well known as a material with excellent properties, but its application is greatly limited due to the harsh methods required for its preparation. This study proposes an innovative carbodiimide-assisted polymerization (CAP) method to simplify the synthesis process of PPTA. The ηinh of the prepared PPTA is 4.97 dl/g. Achieving amidation condensation at normal temperature and pressure, this method is suitable for synthesizing PPTA and allows for the recycling of the condensation reagent, offering a novel approach to green synthesis. Compared to the commercial fiber Kevlar 29, PPTA exhibits similar thermal stability, with negligible decomposition before 500°C. Using the deprotonation method to prepare aramid nanofiber (ANF) resulted in various shapes of bulk materials. The ANF bulk exhibits excellent mechanical properties, with tensile and compressive strengths of 36.9 MPa and 60.68 MPa, respectively, on par with standard engineering materials. Additionally, ANF and PPTA share similar thermal stability. Furthermore, the study prepared aramid nanofiber/partially hydrolyzed polyacrylamide (ANF/HPAM) composite paper, which demonstrated outstanding mechanical performance and thermal stability. The ANF/HPAM composite paper (2% concentration of HPAM) exhibited a tensile strength of 63.32 MPa. These findings offer new insights into developing high-performance fiber materials.

The superior physicochemical properties of layered double hydroxides (LDHs) sets them apart from traditional polylactic acid (PLA) fillers. However, achieving efficient dispersion of LDHs within the PLA matrix poses a challenge in the fabrication of PLA/LDHs nanocomposites. In order to enhance the dispersion of LDHs in the PLA matrix and improve their compatibility with PLA, in this study sodium stearate (SS) and sodium dodecyl sulfate (SDS) were used as surface modifiers and intercalation modifiers for LDHs, respectively. Notably, the strategy of intercalation-surface combined modification for LDHs nanofillers in PLA was explored for the first time. Furthermore, the resulting PLA/LDHs nanocomposites were prepared via a sonication-assisted solution compounding method. The results indicate that the addition of LDHs modified through different methods and concentrations affects not only the thermal properties and crystallinity of the PLA/LDHs composites, but also improves the tensile strength and elongation at break of PLA. Notably, the PLA_LDH_SDS_SS_9% composite exhibited an elongation at break that was 230% higher than neat PLA. This study fills a research gap in the field of PLA/LDHs nanocomposites and establishes a significant foundation for the future preparation and application of these.

In this work, boron nitride nano sheets (BNNSs) were prepared by exfoliation of h-BNs using mono ethylene glycol (MEG) as a novel exfoliating agent. For comparison, isopropyl alcohol (IPA)/water mixture was also used for exfoliation of h-BNs. It was found that using MEG caused preparing nano layers with higher yield and lower thickness compared to the IPA/water mixture. Thereafter, silicon rubber nanocomposites contained 3 and 5 wt% of pure and exfoliated BNNSs were prepared and evaluated for thermal and electrical performances. It was found that h-BNs and exfoliated-BNs drastically enhanced thermal conduction of SR. The silicon rubber contained 5 wt% of the h-BN and exfoliated-BNs illustrated around 20 times higher thermal conductivities compared to pure SR. Exfoliation of h-BNs had negligible effect on improvement of thermal properties, however, it caused 5.7 and 2.3 times enhancement in the electrical volume resistivity compared to the pristine SR and pure h-BN containing nanocomposite, respectively. Both of the BNNSs caused improvement in the heat dissipation performances of SR matrix, however, the exfoliated one with MEG showed better performances. Based on the results, it was claimed that mono ethylene glycol could improve exfoliation of h-BNs and enhance the performances of silicon rubber.

[Display omitted] • The carbodiimide-assisted polymerization is used to synthesize poly(p-phenylene terephthalamide), which is a simple, mild, safe and stable method. • The condensation reagent N,N'-diisopropylcarbodiimide involved in the carbodiimide-assisted polymerization methods is highly efficient and stably recyclable. • Aramid nanofiber materials prepared from self-made poly (p-phenylene terephthalamide) all exhibited favorable mechanical and thermal properties. Poly (p-phenylene terephthalamide) (PPTA), is well known as a material with excellent properties, but its application is greatly limited due to the harsh methods required for its preparation. This study proposes an innovative carbodiimide-assisted polymerization (CAP) method to simplify the synthesis process of PPTA. The η inh of the prepared PPTA is 4.97 dl/g. Achieving amidation condensation at normal temperature and pressure, this method is suitable for synthesizing PPTA and allows for the recycling of the condensation reagent, offering a novel approach to green synthesis. Compared to the commercial fiber Kevlar 29, PPTA exhibits similar thermal stability, with negligible decomposition before 500°C. Using the deprotonation method to prepare aramid nanofiber (ANF) resulted in various shapes of bulk materials. The ANF bulk exhibits excellent mechanical properties, with tensile and compressive strengths of 36.9 MPa and 60.68 MPa, respectively, on par with standard engineering materials. Additionally, ANF and PPTA share similar thermal stability. Furthermore, the study prepared aramid nanofiber/partially hydrolyzed polyacrylamide (ANF/HPAM) composite paper, which demonstrated outstanding mechanical performance and thermal stability. The ANF/HPAM composite paper (2% concentration of HPAM) exhibited a tensile strength of 63.32 MPa. These findings offer new insights into developing high-performance fiber materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • Custom-made filaments of PLA, carbon black, graphite and molybdenum disulfide were fabricated and printed in various architectures and infill densities. • The thermal analysis, acoustic performance, EMI shielding, electrical and thermal conductivity, and heat diffusivity were measured. • The sound absorption shows selective behaviour favouring the best and the lowest infill density and gyroid type of structure. • The EMI shielding is influenced the most by as well the lowest infill density and is less sensitive to the architecture type or formulation of the sample. • The thermal conductivity and heat diffusivity are affected by sample formulation, remaining the best for the highest graphite and MoS 2 concentrations. Fused Filament Fabrication (FFF) is one of the most emerging techniques nowadays. Affordable, easy to use, economical, for a broad audience − from specialists to home users. These are only several of its advantages. A disadvantage is the limited number of available filament types, especially those with high performance. Therefore, the aim of the work was to investigate the properties of custom–made filament printouts based on polylactic (PLA), graphite (G) and molybdenum disulfide (MoS 2). This work looked at structural and thermal analysis, acoustic performance, EMI shielding, and electrical and thermal properties, including thermal conductivity and heat diffusivity. The following were considered during the study: type of printing architecture, infill density, and filament formulations. Among the best values, which were obtained for the highest loaded sample based on 15 wt% graphite and 2 wt% MoS 2 (G15/M2), where EMI shielding effectiveness surpassed SE TOT ∼ 17 dB (per 1 mm sample thickness), electrical conductivity remained at a low level. It exceeded σ ∼ 0.2 S/m; thermal conductivity was slightly over κ ∼ 0.4 W/mK, and heat diffusivity was almost α ∼ 0.4 mm2/s. This work is the first step in designing high-performance materials dedicated to advanced applications based on the FFF technique. [ABSTRACT FROM AUTHOR]

Resin-reinforced Ag sintering materials represent a promising solution for die-attach applications in high-power devices requiring enhanced reliability and heat dissipation. However, the presence of resin and intricate microstructure poses challenges to its thermal performance, and improvement strategies remain unclear. This work utilizes 3D FIB-SEM nanotomography to reconstruct the microstructure of this material under various process conditions. The analysis reveals that, even with an Ag volume fraction as low as 47.3%, Ag particles form a robust 3D network. Geometric tortuosity quantifies the effect of different sintering conditions on the Ag particle network in all spatial directions. Effective thermal conductivity is simulated based on realistic microstructure models. Results show a significant negative correlation between tortuosity and effective thermal conductivity. Increasing sintering temperature in Model B notably reduces tortuosity and enhances effective thermal conductivity. Sensitivity analysis underscores the dominant role of Ag volume fraction in regulating effective thermal conductivity. Finally, transient thermal impedance measurement of this material as a thin die-attach layer in actual high-power devices demonstrated its application potential. This article strives to explore the relationship between process, microstructure, and thermal properties of this material to provide a reference for further development. • 3D FIB-SEM nanotomography meticulously reconstructed and distinguished the microstructure under different process conditions. • Effective thermal conductivity is simulated from a realistic microstructure model using a high-performance cluster. • Tortuosities intuitively reflects the influence of process conditions on the microstructure and thermal properties. • Sensitivity analysis shows the dominant role of Ag volume fraction on the effective thermal conductivity. [ABSTRACT FROM AUTHOR]

[Display omitted] • Introduced a multi-directional freeze-casting technique to create porous ceramics with diverse structural regions. • Sample sizes can be efficiently adjusted by controlling the size and number of freezing sources. • Multi-directional freeze-casting ceramic/polymer composites exhibit isotropic mechanical properties, high specific strength (66.7 kN m/kg), and specific energy absorption (19.2 kJ/kg) among other ceramic/polymer composites. • Multiple-aligned parallel and radially aligned regions induce slant crack propagation and deflection, enhancing energy absorption and isotropic thermal conductivity. Interpenetrating phase composites (IPCs) can combine the distinctive properties of two materials, and customized manufacturing processes are applied to design reinforced skeletons in IPCs. In this study, a porous ceramic featuring diverse structural regions with different direction-aligned pore channels is fabricated by multi-directional freeze-casting. The size of samples can be efficiently adjusted by controlling the size and amount of freezing sources. After infiltration, the resulting multi-directional freeze-casting ceramic/polymer composite (MFCC) has isotropic and satisfactory mechanical properties. Meanwhile, it remains lightweight and performs the highest specific strength (66.7 kN m/kg) and specific energy absorption (19.2 kJ/kg) among tested materials. The vertical-aligned structural regions are responsible for the robust strength, and horizontal-aligned regions prompt energy absorption capacity. Radial-aligned regions induce slant crack propagation and alignment shift between two regions leads to crack deflection, further enhancing energy absorption capacity. Additionally, the MFCC samples with different sizes or pore sizes, demonstrate isotropic thermal conductivity due to the multi-directional alignment of ceramic walls, which provide efficient thermal pathways across different directions. The MFCC and its structural design are promising for enhancing material performance, especially in applications where isotropic mechanical properties and thermal conductivity are important. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ultra-lightweight silicon nitride truss-based structures fabricated via robot-assisted direct ink writing. • Combination of material properties with mechanically efficient/lightweight structures. • UV-assisted Direct Ink Writing of ceramics depends on ink reactivity more than curing depth, enabling freeform ability and homogeneous curing. • Failure behavior modelled by applying a linear elastic fracture mechanics based approach to the results of finite element simulations. • Potential for silicon nitride components with high structural complexity and near-net-shape fabrication. Additive manufacturing techniques have gone beyond their reputation for rapid prototype production and are increasingly adopted for the manufacture of functional components comprising high-end materials and intricate lattice structures. Silicon nitride, renowned for its exceptional mechanical properties and thermal stability, has emerged as a promising candidate for lightweight structural applications. Nonetheless, its high refractive index and density have limited the fabrication of highly complex structures using extrusion and photopolymerization based techniques. In this work, a highly reactive silicon nitride-based ink with high solid loading is developed for the fabrication of ultra-lightweight, truss-based structures. By employing a robot UV-assisted direct ink writing process, it is possible to control the printing head orientation, thus overcoming the limited curing depth of silicon nitride-based inks. The failure behavior of the sintered lattice beam structures under 4-point bending loading has been modeled by applying a linear elastic fracture mechanics (LEFM) based approach to the results of finite element (FE) simulations. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) has gained attention in recent decades. Due to excellent mechanical and thermal properties, pure copper and its alloys are widely in nuclear and aerospace industries. CuCrZr and CuCrNb are precipitation hardenable alloys. The present work provides a comprehensive overview of current research works on CuCrZr and CuCrNb alloys built by various AM processes (especially laser powder bed fusion, L-PBF). Due to high reflectivity for near infrared laser and high thermal conductivity, it is still challenging to build copper alloys by conventional L-PBF process. Therefore, three approaches to enhance the absorptivity of the alloys have been discussed. The microstructure, including texture and precipitates have been discussed. The mechanical, electrical and thermal properties at room temperature and high temperature, anisotropic properties, and post-heat-treatments have been discussed in the review. In addition, the outlook of the AM-ed CuCrZr and CuCrNb alloys has been highlighted.

Inconel 625-NbC Metal Matrix Composite (MMC) is an emergent material of Inconel 625-carbide composites. It is characterized by dense microstructure, improved hardness, and preserved passive Cr-rich layer formation during oxidation. In this study, its thermal properties were investigated. Inconel 625-NbC composites and Inconel 625 reference alloy were consolidated by Spark Plasma Sintering (SPS). Their microstructure, phase composition, Coefficient of Thermal Expansion (CTE), thermal diffusivity (α), thermal conductivity (λ), and specific heat (cp) were studied. The addition of NbC into Inconel 625 matrix did not significantly affect the CTE or λ of the final composite. Thermal conductivity of Inconel 625-NbC was initially lower than 625 superalloy but was increasing faster in function of temperature. cp functions of SPS-ed 625 alloy and composites had different slopes in comparison to literature. The influence of hot rolling, part of Inconel 625-NbC obtaining SPS technology, was also studied. It affected composites cp.

A large number (greater than 150) of porous steatite ceramic rods were prepared using different types of renewable plant fiber products as pore-forming agent with mass contents ranging from 2 to 10%. In addition, dense steatite ceramics were synthesized for comparison within a gas furnace at sintering temperatures between 1300 and 1350 °C. High-resolution 3D X-ray microscopy facilitated a non-destructive, direct investigation of the three-dimensional pore space and microstructure. By using image-based pore space analysis, various pore space parameters, such as, e.g., pore volume, pore-size distribution, and pore connectivity were determined. In addition to the characterization of the pore space, phase analysis, structural and chemical investigations were carried out by X-ray powder diffraction, electron microscopy, Fourier-transform infrared, Raman and X-ray spectroscopy. Finally, to evaluate the influence of characteristics on the physical properties, elastic, strength and thermal properties were determined. With the increase of porosity, the flexural strength and thermal conductivity values decrease from σf = 123 ± 8 to 37 ± 5 MPa and λ = 3.22 ± 0.02 to 1.77 ± 0.02 W/(m·K), respectively. The obtained experimental results were discussed by means of micromechanical models, highlighting the effect of pore-space morphologies on the physical performance of porous steatite ceramics.

Carbon materials reinforced copper matrix composites with excellent mechanical properties, high thermal conductivity (TC) and suitable coefficient of thermal expansion (CTE) are expected to meet the urgent need for the thermal management materials with structural stability and efficient heat dissipation in civil and military fields. In this work, the tungsten-copper (W-Cu) composite coating was deposited on the graphite flakes (GFs) by the impregnation-reduction and ultrasonic-assisted electroless plating. Meanwhile, the W-Cu coated GFs reinforced Cu matrix composites (GFs(W-Cu)/Cu) were also prepared by the vacuum hot-pressing sintering. Based on the microstructure and surface analysis, the interfacial bonding has changed from the simple mechanical connection to the mechanical-metallurgical synergy. As for the three-point bending and uniaxial tensile tests, the largest in-plane, through-plane flexural strength and tensile strength of the GFs(W-Cu)/Cu composite can achieve the values of 189.6 ± 3.8, 172.3 ± 4.2 and 91.9 ± 2.6 MPa, respectively. Among the GFs(W-Cu)/Cu composites, the ultrahigh in-plane TC and lowest through-plane CTE can reach 929.8 ± 5.0 Wm−1K−1 and 6.3 ± 0.2 ppmK−1 respectively, and the better thermal response rate can be 0.67 °C·s−1. In conclusion, an effective way to develop the structural and functional integrated carbon-based thermal management materials can be provided.

Refractory complex concentrated alloys are an emerging class of materials that attracts attention due to their stability and performance at high temperatures. In this study, we investigate the variations in the mechanical and thermal properties across a broad compositional space for the refractory MoNbTaTi quaternary using high-throughput ab-initio calculations and experimental characterization. For all the properties surveyed, we note a good agreement between our modeling predictions and the experimentally measured values. We reveal the particular role of molybdenum (Mo) to achieve high strength when in high concentration. We trace the origin of this phenomenon to a shift from metallic to covalent bonding when the Mo content is increased. Additionally, a mechanistic, dislocation-based description of the yield strength further explains such high strength due to a combination of high bulk and shear moduli, accompanied by the relatively small size of the Mo atom compared to the other atoms in the alloy. Our analysis of the thermodynamics properties shows that regardless of the composition, this class of quaternary alloys shows good stability and low sensitivity to temperature. Taken together, these results pave the way for the design of new high-performance refractory alloys beyond the equimolar composition found in high-entropy alloys.

An entropy-stabilization strategy was applied to engineer a novel thermal insulating material by establishing a single-phase solid solution with the formula of (Y1/2Yb1/2)2(Ti1/3Zr1/3Hf1/3)2O7 (YYHEO). Structural analysis revealed that this material exceeded the typical substitutional solubility limit, even with a significant atomic size difference, where the conventional determination rule was defied. YYHEO exhibited a lower glass-like thermal conductivity due to its highly disordered crystal structure and the specific design strategy. The coefficient of thermal expansion and mechanical properties (e.g. elastic modulus and hardness) were comparable to conventional materials, suggesting that YYHEO is a promising candidate for application as a new thermal insulating material.

[Display omitted] • The feasibility of obtaining low thermal expansion (LTE) Fe-Ni alloys using T-WAAM is investigated. • Deposition mode affects the stability of the melt pool and the resulting chemical composition. • Stability in deposition and composition is achieved with the continuous metal transfer mode during the T-WAAM process. • The as-deposited LTE alloys exhibit thermal properties comparable to the conventionally produced alloys. The binary Fe–Ni system offers alloys with notably low linear coefficients of thermal expansion (CTE), contingent upon their Ni content. In this respect twin-wire arc additive manufacturing (T-WAAM) presents the opportunity of in-situ alloying through the simultaneous feeding of two metal wires into a weld pool to obtain desired alloy compositions. This study aims to deposit a graded wall with Ni contents targeted at 42, 46, and 52 wt% in the building direction of the wall, along with a block comprising of 46 wt% Ni, employing the T-WAAM approach. The results show effective incorporation of additional Ni into the weld pool and geometrically stable weld beads in the continuous metal transfer mode during the T-WAAM process. This mode led to the defect-free and chemically stable deposition of the graded wall and the block with average Ni contents of 42.3 ± 1.1, 45.8 ± 1.4, 52.6 ± 0.8 wt%, and 46.4 ± 0.9 wt%, respectively. The measured Curie temperatures of the as-deposited alloys and the mean CTE values of alloy 46 were found to be comparable to the commercial alloys. In summary, this study validates the feasibility of in-situ deposition of low thermal expansion alloy compositions, thereby enabling the possibility of on-demand thermal expansion properties. [ABSTRACT FROM AUTHOR]

[Display omitted] • The cold sintering process (CSP) showed excellent energy-efficient benefits. • The densification mechanism of ultra-low temperature sintering (150 °C) was revealed. • The sample exhibited high strength retention and good thermal properties under simulated lunar environments. Sintering lunar regolith simulants as building materials is an effective method to establish long-term lunar bases. However, the high energy consumption of conventional thermal sintering is a challenge for energy-scarce lunars. The cold sintering process (CSP), which densifies ceramics with the assistance of transient solvent, offers a solution to overcome the aforementioned problems. Utilizing the CSP at 150 °C, 200 MPa, and 15 wt% 10 mol NaOH for 90 min, the density and compressive strength of the samples reached 2.44 g/cm3 and 207 MPa, respectively. The energy consumption of CSP equipment is only 0.86 kW·h, which is 6.66 times lower than that of conventional thermal sintering (5.73 kW·h). Furthermore, the compressive strength of the samples after three cool-heat cycles temperature between −196 °C and 150 °C was 205 MPa, indicating that the samples maintained high reliability in a simulated lunar environment. This excellent performance is attributed to the NaOH solution dissolving the oxide clusters on the particle surface, and the precipitation-generated glass phase connecting adjacent particles, making the particles consolidated and densified. Therefore, the cold sintering process presents promising prospects for the energy-efficient fabrication of lunar construction materials with excellent mechanical strength and durability. [ABSTRACT FROM AUTHOR]

[Display omitted] • The high throughput calculations screening method is successfully used to design the components of high-entropy RE-disilicate. • Five novel high-entropy RE-disilicates were prepared with excellent thermal performance through the composition design effectively. • Revealed the relationship between the electronic structure and thermal properties under the influence of Sc. The configuration entropy was manipulated by introducing atoms with unique properties using the high throughput calculations, and five new disilicates with ideal properties which have lower thermal conductivity and controllable thermal expansion coefficient were obtained through composition design. From a microstructural perspective, the inclusion of atoms with larger ionic radius differences (reaching a 4.11 % contrast with Yb 2 Si 2 O 7) can cause sever lattice shrinkage (9.49 % compared to single-component disilicates), which leads to lower thermal conductivity and a change in the thermal expansion coefficient. At 1200 °C, the thermal expansion coefficient of the five high-entropy disilicates ranged from 4.57 × 10-6 K−1 to 4.84 × 10-6 K−1, and the minimum thermal conductivity was only 1.14 W/m·K. Additionally, the local charge disorder facilitates the transfer of electrons around Si-O to Sc, which reduces the covalent bond strength of Si-O and regulates the thermal expansion coefficient. This phenomenon has been proved in the five non-equimolar high-entropy disilicates with different contents of Sc, effectively regulating the thermal expansion coefficient in 4.08 × 10-6 K−1 to 5.04 × 10-6 K−1. This study presents a novel method for controlling the thermal properties of disilicates and expands the possibilities for selecting thermal protective coating materials for ultra-high temperature SiC-based ceramic composites. [ABSTRACT FROM AUTHOR]

Abstract An aluminum material stabilized with a 1.6 vol% of nanometric Al 2 O 3 dispersoids, named HITEMAL, was fabricated by hot extrusion of a fine atomized Al powder. The Al 2 O 3 dispersoids stemmed from a native Al 2 O 3 films on an aluminum powder surface. An extruded rod of the material was then cold-deformed out into a thin wire by rotatory swaging, hydro extrusion and rolling. Such severely deformed HITEMAL was studied as a prospective outer sheath stabilizer material for MgB 2 core superconductor wires. An emphasis was put on the effect of annealing realized at various temperatures close to the melting point of Al, which is typically applied to form an in-situ MgB 2 superconductive core, on the mechanical and electrical properties of the HITEMAL wire. A systematic investigation was performed of changes to a severely deformed Al grain structure and Al 2 O 3 dispersoids upon annealing the as-deformed wire from 595 to 655 °C for 30 min. Mechanical and electrical properties of the wire were measured at room and cryogenic temperatures. The results showed that the ultrafine-grained Al + 1.6 vol% Al 2 O 3 wire exhibited advantageous properties, and surface integrity after annealing up to 642 °C. It is thus a lightweight material of choice for outer sheaths of MgB 2 superconductors. Graphical abstract Unlabelled Image Highlights • Al wire fabricated from a fine Al powder was studied as outer sheath material for lightweight MgB 2 superconductors. • The effect of annealing realized at 595-655 °C on microstructure, mechanical and electrical properties was investigated. • The as-rolled wire showed ultrafine-grained Al structure with 1.6% of nanometric Al 2 O 3 dispersoids dispersed in Al matrix. • The Al 2 O 3 dispersoids effectively stabilized Al grain structure during annealing, and only minor Al grain growth occurred. • Wires annealed up to 642 °C showed attractive strength and electrical resistivity at room and cryogenic temperatures. [ABSTRACT FROM AUTHOR]

Abstract Additive Manufacture (AM) enables the fabrication of highly complex lattice structures with exceptional engineering properties. Inconel is a technically useful material in that it provides high resistance to oxidisation, creep and loss of mechanical properties at elevated temperatures. The combination of Inconel material properties and the geometric freedom of AM provides a unique opportunity for the fabrication of engineered structures with exceptional strength and stiffness at elevated temperatures, as for example is required for high temperature turbomachinery. Despite the associated technical opportunities, there exists no design data on the mechanical response, deformation characteristics and failure modes of AM Inconel 625 lattice structures. This research provides a comprehensive reference for the mechanical response of Inconel 625 lattice structures fabricated by Selective Laser Melting (SLM). Furthermore, the high ductility of Inconel 625 lattice enables novel insight into the structural mechanics of AM lattice, and the associated deformation photography provides a reference for the validation and verification of numerical models of AM lattice behaviour. Graphical abstract Unlabelled Image Highlights • A comprehensive reference of the mechanical response of Inconel 625 (IN625) lattice structures made by Selective Laser Melting (SLM) is provided. • Mechanical performance was measured including yield strength, Young’s Modulus and associated density specific properties for mass limited design. • IN625 lattice structures display exceptional ductility presenting attractive opportunities for energy absorption applications. • Adjustment of topology and cell size can enable coarse and fine tuning of lattice mechanical properties. • This previously unavailable IN625 lattice experimental data provides a reference for design application and numerical models validation. [ABSTRACT FROM AUTHOR]

[Display omitted] • The as-deposited AlCrFeCoNiCu 0.5 films were annealed at 500 °C for up to 72 h. • Four new phases were formed during the 72 h of annealing. • The formation of a new heterogeneous nanocomposite thin film was revealed. • A 30% enhancement of mechanical properties was achieved after 72 h annealing. • The as-annealed thin films exhibited superior thermal stability. High entropy alloy (HEA) films offer excellent mechanical properties due to their random solid solution structure. However, their large grain boundary volume fraction can cause thermal instability, resulting in phase decomposition that affects their high-temperature performance. Nevertheless, it remains an interesting question whether phase decomposition can be used as a processing tool to create new HEA materials. In this study, AlCrFeCoNiCu0.5 HEA thin films were fabricated and annealed at 500 °C for up to 72 h. The 72-hour annealed thin film exhibited a 30 % increase in mechanical properties, exceeding most other HEA thin films. Characterization using X-ray and electron microscopy revealed a decomposition-induced phase transformation, which produced four new phases, including Cu-rich FCC phase, Cr-rich BCC phase, and ordered B2 phase of AlNi and FeCo. The enhanced mechanical properties were due to back stress strengthening and BCC + B2 phase strengthening. The 72-hour annealed thin film also showed excellent thermal stability through a new round of annealing, exhibiting a low variation in microstructure and chemical composition after being annealed at 500 °C for 100 h. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel Sc/Zr/Ti/Er modified Al-Cu alloy was successfully fabricated by wire-arc directed energy deposition technology. • The fine equiaxed grain structure was obtained due to the heterogeneous nucleation caused by the primary Al3X dispersoids. • Homogenization prefabricates more Al3X dispersoids, which promote the transition from θ″ to θ′ precipitate. • Homogenization ripens the existing pores, resulting in a better tensile isotropy. In this study, a novel Sc/Zr/Ti/Er-modified 2219 aluminum alloy was designed and wall-shaped components were then fabricated by wire-arc directed energy deposition (DED). Due to the heterogeneous nucleation promoted by primary Al 3 X dispersoids, the as-deposited alloy exhibits a highly equiaxed fine grain structure. Two heat treatment schedules were conducted to tailor the strength and thermal stability of the alloy. Compared with the classical T6 heat treatment, the additional homogenization step before the T6 heat treatment (HT6) prefabricated more Al 3 X dispersoids, which indirectly promoted the transition from θ″ precipitates to θ′ precipitates, resulting in a slight reduction in strength. However, this homogenization step helps to avoid the aggregation of pores by promoting pores ripening and significantly alleviates the anisotropy of ductility. In addition, the better thermal stability of the HT6 heat treated alloy is due to more Al 3 X dispersoids and finer θ′ precipitates with high coarsening resistance caused by the segregation of Sc and Mn at the θ′/Al interface during thermal exposure. In general, the wire-arc DEDed micro-alloyed 2219 Al alloy exhibits a promising combination of strength and ductility after heat treatment and its mechanical properties are superior to those of the wrought micro-alloyed Al-Cu alloys. [ABSTRACT FROM AUTHOR]

[Display omitted] • The LDHs nanofillers for PLA were successfully modified by intercalation-surface combined modification strategy. • Modified LDHs can alter the crystallinity of PLA/LDHs nanocomposites within the range of 10.1% to 47.3%. • The incorporation of organically modified LDHs simultaneously enhances the tensile strength and elongation of PLA composites. • The addition of LDHs modified through combined modification can enhance the elongation at break of PLA by up to 230%. The superior physicochemical properties of layered double hydroxides (LDHs) sets them apart from traditional polylactic acid (PLA) fillers. However, achieving efficient dispersion of LDHs within the PLA matrix poses a challenge in the fabrication of PLA/LDHs nanocomposites. In order to enhance the dispersion of LDHs in the PLA matrix and improve their compatibility with PLA, in this study sodium stearate (SS) and sodium dodecyl sulfate (SDS) were used as surface modifiers and intercalation modifiers for LDHs, respectively. Notably, the strategy of intercalation-surface combined modification for LDHs nanofillers in PLA was explored for the first time. Furthermore, the resulting PLA/LDHs nanocomposites were prepared via a sonication-assisted solution compounding method. The results indicate that the addition of LDHs modified through different methods and concentrations affects not only the thermal properties and crystallinity of the PLA/LDHs composites, but also improves the tensile strength and elongation at break of PLA. Notably, the PLA_LDH_SDS_SS_9% composite exhibited an elongation at break that was 230% higher than neat PLA. This study fills a research gap in the field of PLA/LDHs nanocomposites and establishes a significant foundation for the future preparation and application of these. [ABSTRACT FROM AUTHOR]

Al matrix composites reinforced with Cu-coated pitch-based carbon fibres (Al/Cu-CFs) were fabricated, using a novel combination of rheocasting and equal channel angular extrusion (ECAE) techniques, in order to exploit the thermal conductivity ( K ) of the material. Rheocasting allowed the introduction and dispersion of Cu-CFs within the Al 3 Mg matrix. The subsequent ECAE processing reduced the porosity of the composites from 3 to 0.03% and induced a high degree of fibre alignment within the matrix, although considerable damage to the fibres occurred during this processing step. After 6 ECAE passes, in which the billet orientation remained constant, the composite with the highest degree of fibre alignment show a thermal conductivity ( K ) improvement of ~20% with respect to the rheocast composite. The improvement is due to porosity reduction, improved fibre alignment and forced intimate contact of clean CF surfaces with the matrix. [ABSTRACT FROM AUTHOR]

Diamondene can be formed by compressing two or more layers of graphene. As a sp 2 / sp 3 orbital hybridized two-dimensional material, its physical properties are different from either graphene or diamond. This new material is ultrahard on a SiC substrate. Here, we focus on the thermal stability and the basic mechanical properties of diamondene without passivation. We used molecular dynamics calculations to show that diamondene has isotropic thermal expansion at temperature below 280 K. At room temperature, it is unstable. When stretched along the armchair direction, diamondene has a maximum elastic strain that is higher than 0.17. It then experiences further plastic deformation before collapse. However, when stretched along the zigzag direction, the maximum elastic strain is higher than 0.3, e.g., 0.318 at 250 K. The ribbon collapses soon after the strain exceeds the critical value. Hence, diamondene has an elastic-brittle property along the zigzag direction. This excellent elasticity is significant for applications of diamondene in a flexible device. [ABSTRACT FROM AUTHOR]

Poly( l -lactide) (PLLA) is a biodegradable bioplastic that has been widely investigated for use instead of petroleum-based plastics. However, its practical applications have been limited by its brittleness. Herein, a high molecular weight triblock copolymer of poly( l -lactide)- b -poly(ethylene glycol)- b -poly( l -lactide) (PLLA-PEG-PLLA) was synthesized by ring-opening polymerization of l -lactide using stannous octoate and PEG as the initiating system. The effect of an epoxy-based chain extender on the thermal properties, melt flow index (MFI), phase morphology and tensile properties of the PLLA-PEG-PLLA were investigated and compared to PLLA homopolymer. Chain-extended PLLA-PEG-PLLA and its films were prepared by reactive melt blending and compression molding, respectively. The flexible PEG blocks significantly improved both crystallization of PLLA blocks and strain at break of PLLA-PEG-PLLA films. The chain extension can decrease MFI of both the PLLA and PLLA-PEG-PLLA but their crystallizabilities were suppressed. All the PLLA-PEG-PLLA films with and without chain extension had no phase separation. The tensile properties of PLLA-PEG-PLLA films increased by the chain extension. The results showed that the chain-extended PLLA-PEG-PLLA have potential for use as highly flexible bioplastics. [ABSTRACT FROM AUTHOR]

Choice of alkali cation in mix design of geopolymers is critical for their thermal performance. However, the influence of alkali cation type on strength endurance of geopolymers subject to high temperature exposure and the underlying governing mechanisms have not been studied. This study investigated the effects of alkali cation type on high temperature response of fly ash geopolymers aiming towards structural applications. In-depth investigation was carried out to discover the underlying mechanisms governing the strength endurance of fly ash geopolymers subject to high temperature exposure and its correlation with their volume stability and chemical stability. Results showed that potassium geopolymer exhibited significant strength enhancement (30–40%) and sodium geopolymer displayed reduced strength (10%), and the strength of mixed sodium and potassium geopolymer remained unchanged after exposure to elevated temperature. While the binders were chemically stable without deterioration and formation of new crystal phases after high temperature exposure, the volume stability varied with the type of alkali cation used. Formation of cracks and gel densification due to shrinkage, and healing of micro-cracks and change of pore sizes due to sintering were identified as responsible mechanisms at different temperature ranges. While crack development and enlargement of pores lowered the strength, densification of matrix and healing of micro-cracks favored strength gain. These competing mechanisms determine the strength endurance of geopolymers depending on the type of alkali cation used. Overall, it shows that geopolymers can be tailored, such that stable (or even enhanced) strengths upon thermal exposure are realized, for structural applications. [ABSTRACT FROM AUTHOR]

A facile approach to fabricate a surface nanocomposite structure by embedding SiC nano-particles (NPs) via laser micro-melting is reported. A high fidelity model is adopted to reveal transient temperature distributions and the embedding of the SiC NPs into an Al molten pool during laser micro-melting. Special attention is paid to the embedding dynamic behaviours within the molten pool affected by Marangoni convection. Fluid flow and migration characteristics of the SiC NPs into the molten pool, as well as the resultant bubble motion and pore defects formation, are considered. Simulation results show that the temperature distribution is basically symmetrical with respect to the laser beam, and the Marangoni convection in the molten pool tends to embed the SiC NPs into the Al surface layer together with gas bubbles. This phenomneon is well validated by the experimental study on the surface morphology and the SiC NPs distribution in the Al surface layer. Microstructural characterizations indicate that a relatively flat reinforced SiC/Al surface can be formed at an optimized laser energy of 0.6 J. These studies may provide a new strategy for constructing nanocomposite structure on metal alloy surface. [ABSTRACT FROM AUTHOR]

In this paper, electrically actuated shape memory composites were prepared by compounding shape memory polyurethane (SMPU) with conductive antimony-doped tin oxide/TiO 2 (ATO/TiO 2 ) whiskers. The resultant composites, ATO/TiO 2 /SMPU, can be activated by electric voltages because of heating Joule and enhancement of heating efficiency by the conductive network resulting from the overlaps of whiskers. In addition to conductivity, ATO/TiO 2 /SMPU composites featured lighter color than most electroactive shape memory composites, which exhibit black color due to the addition of carbon materials. The composites exhibited uniform electrical resistance and rapid heat transfer performances. When the composites with 50 wt% ATO/TiO 2 whiskers were used in a switch electric circuit as the switch, the circuit can turn off within 30 s. ATO/TiO 2 whiskers improved Young's moduli by at least 390% and recovery stresses by more than 250% compared with pristine SMPU. Although the recovery rates were unsatisfactory in the first test cycle, composites with 40 wt% ATO/TiO 2 whiskers and 50 wt% ATO/TiO 2 whiskers still showed recovery rates higher than 96% and 94% in the third cycle, respectively. [ABSTRACT FROM AUTHOR]

The Ti/TiAl metal-intermetallic laminates were fabricated by hot-pressing starting from the elemental Ti and Al foils. The final microstructures of laminates consist of alternating layers of ductile Ti and brittle intermetallic. The relationships between mechanical properties and layer sequence of Ti/TiAl laminates have been studied by examining the effects of solid solubility of Al in Ti layer, the volume fraction of intermetallic layer and the interlayer spacing. In these three cases, the samples with the best performance are obtained and among them the optimal sample is confirm with fracture strength 752 MPa, K IC 48 MPa·m 1/2 . In particularly, a novel theoretical formula of strength calculation is proposed according to the mixing rule of composites. The theoretically calculated results agree well with the experimental results. [ABSTRACT FROM AUTHOR]

The microstructure design strategy is introduced to improve the mechanical property of a novel γ-Ti-43.5Al-6.5Nb-1.5Cr-0.5C/TiB 2 metal matrix composite (MMC) fabricated by hot isostatic press (HIP). With increasing the content of TiB 2 from 0 to 3 wt%, the average grain size, {001} maximum texture index and average schmid factor of HIP-processed Ti-43.5Al-6.5Nb-1.5Cr-0.5C/TiB 2 parts generally decrease from 27.4 μm, 7.9 and 0.43 to 22.7 μm, 4.1 and 0.38, in addition, the crystallographic texture transforms from the mixture of (001) and (111) orientations to a strong (101) orientation. The phases evolution mechanism in the HIP-processed Ti-43.5Al-6.5Nb-1.5Cr-0.5C/TiB 2 parts can be divided into four steps: first of all, β phase transforms to γ and α phases, then, a small amount of new phases of TiB and TiC emerge by the diffusion of Ti and C atoms, subsequently, the β and α orderly transform to B 2 and α 2 , lastly, the B 2 , α 2 , TiB 2 , TiB and TiC uniformly distribute in the γ matrix. Both the tensile strength and strain of HIP-processed Ti-43.5Al-6.5Nb-1.5Cr-0.5C/TiB 2 components increase from 471.9 MPa and 1.7% to 653.4 MPa 2.1% with the increase of TiB 2 content from 0 to 3 wt%. [ABSTRACT FROM AUTHOR]

Conventional polyimide nanocomposites reinforced with graphene-based nanofillers usually possess excellent properties, such as high thermal decomposition temperature, enhanced tensile strength, tensile modulus, etc. However, the elongation at break of the nanocomposites is reduced. Here, we prepared N-doped graphene quantum dots/colorless polyimide nanocomposite (N-GQDs/CPI) films for the first time by in-situ polymerization, whose elongation at break is about 2 times that of the pure film. Meanwhile, the thermal properties and other mechanical properties of the films are improved. Through analyzing FT-IR, XPS, XRD, TAG SEM, etc. of N-GQDs and the films, we consider that the strengthening mechanism of matrix performance is attributed to N-GQDs' well dispersion, its small size effects and strong interface interaction with the matrix. Furthermore, at the indicative wavelength of 550 nm, the optical transmittance of the film with 1 wt% N-GQDs still maintains 79%, indicating the resulting films have excellent optical transmittance. The hydrophilic properties of the prepared films' surface is reduced, their water surface contact angle are increased from 63 ± 2.7° to 92 ± 1.7° with the content of N-GQDs increasing. This research shows that N-GQDs can enhance the various properties of polyimide and provides a high performance nanocomposite films for potential flexible substrates. [ABSTRACT FROM AUTHOR]

Graphene holds great potential in metal matrix composites for thermal management due to its excellent thermal properties. However, the graphene/metal composites possessing both high thermal conductivity (TC) and low coefficient of thermal expansion (CTE) have not yet been realized. Herein, we reported an efficient strategy to achieve a high alignment of graphene nanosheets (GNSs) in GNS/Cu composites through a vacuum filtration method followed by spark plasma sintering. Because of the highly aligned GNSs and laminated structure, the GNS/Cu composites exhibited notably anisotropic thermal properties. Intriguingly, the composites showed a reversed anisotropic behavior between TC and CTE as a function of GNS fraction, in which the in-plane TC was substantially higher than through-plane TC, whereas oppositely the through-plane CTE displayed a larger drop than in-plane CTE. Promisingly, the composite with 30 vol% GNSs delivered a high in-plane TC of 458 W/mK and a low through-plane CTE of 6.2 ppm/K, corresponding to a 35% TC enhancement and a 64% CTE reduction compared to pure Cu, respectively. The present GNS/Cu composites with high in-plane TC and low through-plane CTE are promising candidates for specific thermal management applications that require an efficient in-plane heat dissipation but a good through-plane dimensional stability. [ABSTRACT FROM AUTHOR]

This work reports the effect of acrylated epoxidized soybean oil (AESO) addition on the mechanical, thermal, and thermomechanical properties of polylactide (PLA) parts obtained by injection molding. To this end, AESO, a chemically multi-functionalized vegetable oil, was incorporated into PLA during melt processing. The PLA parts with AESO contents in the 2.5–7.5 wt% range showed a remarkable enhancement in both elongation at break and impact-absorbed energy while their tensile and flexural strength as well as thermomechanical properties were maintained or slightly improved. Additionally, the AESO-containing PLA parts presented higher thermal stability and lower crystallinity. The improvement achieved was ascribed to a dual effect of plasticization in combination with a chain-extension and/or cross-linking process of the PLA chains by the highly reactive acrylate and epoxy groups present in AESO. The use of AESO thus represents an environmentally friendly solution to obtain toughened PLA materials of high interest in, for instance, rigid packaging, automotive or building and construction applications. [ABSTRACT FROM AUTHOR]

The structural transition and thermal properties (thermodynamic and thermoelastic properties) of Ni 3 Nb-D0 22 phase are investigated by first-principles combined with quasi-harmonic approximation method. The computed results show that the structural transition from Ni 3 Nb-D0 22 to Ni 3 Nb-D0 a primitively occurs at the temperature range of 950–960 K. The phase structure is thermally stable but easily compressed. The heat capacity tends to Dulong-Petit limit when the temperature is higher than 900 K. The computed thermoelastic properties of Ni 3 Nb-D0 22 phase reveal the slight softening trends with the increased temperature, indicating that the Ni 3 Nb-D0 22 phase is well heat-resistance. Additionally, Ni 3 Nb-D0 22 phase is ductile at the temperature range of 0–900 K, and its hardness decreases with the increased temperature. Moreover, the Ni 3 Nb-D0 22 phase is anisotropic and has a distinct dependence on crystal orientations. The strengths of chemical bond along [100] and [010] orientations on (001) plane are slightly weakened with the increase of temperature. [ABSTRACT FROM AUTHOR]

Tremendous properties of bulk metallic glasses (BMGs) have led to numerous potential applications in the past few years. An obvious interest has been given to their potential as structural material given their high mechanical properties and their ability to be produced in bulk parts of several millimeters in size. Unlike their crystalline counterparts, they also show very promising insulating properties due to the absence of a periodic lattice. In the present work, the interest of using bulk amorphous metallic alloys as materials combining good structural properties and thermal insulation is discussed. The study of Hf-rich BMGs enables to reduce the thermal losses through a higher σ c / κ performance ratio and thus shows very good potential for future insulating and structural applications. [ABSTRACT FROM AUTHOR]

Macro/mesopore SiOC ceramic monoliths of anisotropic structure were prepared by freeze casting, using methy phenyl polysiloxane (H44) or methy polysiloxane (MK) and (3-aminopropyl)triethoxysilane (APTES) as precursors. Influence of pyrolysis and testing temperature on compressive strength was investigated. Monoliths pyrolyzed at 700 °C had the highest compressive strength both at 77 K (14.0 ± 4.3 MPa) and 293 K (7.7 ± 1.8 MPa), regardless of precursors. Compressive strength of monolith in parallel direction is around twice as much as perpendicular direction. Compressive strength of both monoliths in liquid nitrogen (77 K) was around twice of that in air (293 K) probably due to low temperature and liquid resistance. Anisotropic expansion was observed, and the shrinkage in parallel direction was almost twice of that in perpendicular direction, which can be verified by the Schapery equation. Monolith made from H44 showed a much higher coefficient of thermal expansion at 77 K than monolith made from MK and APTES, probably due to difference in composition and measurement condition. Thermal conductivities and specific heat capacities displayed an upward trend from low to warmer temperature. The minimum and maximum values for thermal conductivity are 0.2 and 1.2 W m − 1 K − 1 . The maximum heat conductivities might be determined mainly by the macroporosity and the thermal conductivity of the hybrid material. [ABSTRACT FROM AUTHOR]

[Display omitted] • The thermal transport of 4D printed shape memory polymers strongly depends on their programmed deformation due to the interplay of conduction and radiation effects. • Stretching-dominated architecture enables sharp thermal conductance tuning due to buckling. • Bending-dominated architecture enables fine thermal conductance tuning in the absence of buckling. • 4D printed shape memory polymer mechanical metamaterials with unique deformation and shape recoverability mechanisms can lead to a novel thermal switch. Here the authors present an active thermal control system using 4Dprinted shape memory polymers and demonstrate how distinct deformation mechanisms lead to unique, tunable thermal properties using stretching- and bending-dominated architectures. Infrared thermography measurements with varying temperature and compression settings show that at low strains, radiation drives the effective conductance increase as the view factors among the struts increase with increasing strain, and at higher strains, conduction drives the effective conductance increase as the strut-to-strut contact areas increase. The effective thermal conductance increases from 4.41 m W / K to 14.52 m W / K and from 3.23 m W / K to 10.48 m W / K for the Kelvin foam and octet-truss microlattices, respectively, as strain increases from 0 % to approximately 70 %. As the strain is adjusted, the stretching-dominated octet-truss architecture exhibits abrupt changes in shape and conductance due to buckling. The bending-dominated Kelvin foam architecture allows for gradual geometric changes and precise tuning of thermal conductance. These findings provide a new understanding of thermal transport phenomena in 4D-printed metamaterials, which may be a breakthrough in tunable thermal systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hexagonal boron nitride (h-BN) nano sheets were prepared from nanoparticles by a novel/effective exfoliating agent (i.e. mono ethylene glycol). • Exfoliation of h-BN was performed much better in mono ethylene glycol as replacing solvent for water/isopropyl alcohol. • Silicon rubber (SR) nanocomposites were prepared using pure and exfoliated h-BNs and evaluated for thermal and electrical properties. • The exfoliated h-BNs caused considerable improvement in the thermal conductivity and electrical resistance of SR compared to pure h-BNs. In this work, boron nitride nano sheets (BNNSs) were prepared by exfoliation of h-BNs using mono ethylene glycol (MEG) as a novel exfoliating agent. For comparison, isopropyl alcohol (IPA)/water mixture was also used for exfoliation of h-BNs. It was found that using MEG caused preparing nano layers with higher yield and lower thickness compared to the IPA/water mixture. Thereafter, silicon rubber nanocomposites contained 3 and 5 wt% of pure and exfoliated BNNSs were prepared and evaluated for thermal and electrical performances. It was found that h-BNs and exfoliated-BNs drastically enhanced thermal conduction of SR. The silicon rubber contained 5 wt% of the h-BN and exfoliated-BNs illustrated around 20 times higher thermal conductivities compared to pure SR. Exfoliation of h-BNs had negligible effect on improvement of thermal properties, however, it caused 5.7 and 2.3 times enhancement in the electrical volume resistivity compared to the pristine SR and pure h-BN containing nanocomposite, respectively. Both of the BNNSs caused improvement in the heat dissipation performances of SR matrix, however, the exfoliated one with MEG showed better performances. Based on the results, it was claimed that mono ethylene glycol could improve exfoliation of h-BNs and enhance the performances of silicon rubber. [ABSTRACT FROM AUTHOR]

[Display omitted] • Microfluidics can be used to prepare homogeneous and uniformly mixed energetic microspheres containing octogen and copper–aluminum composite particles. • The introduction of copper can promote the thermal decomposition of octogen. • Copper-aluminum composite particles instead of aluminum for the preparation of octogen composite microspheres can shorten the ignition delay and increase the combustion rate of the microspheres. Aluminized explosives are widely used in military applications. However, the easy agglomeration of aluminum (Al) powder and its high ignition temperature greatly hinder the reaction of nano aluminum (n-Al) in the process of explosion, thus affecting the combustion and explosion of aluminum-containing explosives. In the present study, copper (Cu) coated n-Al composite particles were introduced into aluminized explosives, and Cu coated n-Al composite particles and ball-milled octogen (HMX) energetic microspheres were prepared via droplet microfluidic technology using binder. The morphology, crystal form, thermal properties, combustion, and mechanical sensitivity of the microspheres were studied using a variety of techniques. The prepared microspheres had regular spherical morphology and uniform particle size, with an even distribution of particles. Using microfluidic technology will not destroy the crystal form of each particle. The introduction of Cu promoted the thermal decomposition of HMX. The mechanical sensitivity of the prepared Cu/Al microspheres was lower than that of the microspheres only containing n-Al. The Cu/Al microsphere samples exhibited excellent and stable combustion performance, and that the addition of Cu increased the combustion speed compared to the microspheres only containing n-Al. This technology represents an inexpensive and simple way to improve on existing aluminized explosives. [ABSTRACT FROM AUTHOR]

A novel lightweight organic aerogel-impregnated low-density carbon/carbon (C/C) composite was produced through vacuum impregnation using carbon-bonded carbon fibre (CBCF) as substrate and resorcinol-furfural (RF) aerogel as infiltrant. Microstructural analysis showed that fibres in CBCF were uniformly coated with a thin layer of aerogels, acting as the supporting skeletons, to strengthen the aerogel matrix. The as prepared RF-C/C possessed low densities between 0.26 and 0.37 g/cm 3 , relatively high compressive strength, ranging from 0.45 to 3.27 MPa, and low thermal conductivities of 0.105 to 0.350 W/(mK) at room temperature. Furthermore, good thermal ablative and insulative properties (recession rates as low as 0.082 mm/s and internal temperature peaks below 90 °C at 38 mm in-depth position as the surface temperature exceeded 2000 °C) under an atmospheric re-entry condition. From mentioned above, RF-C/C present huge application prospects in heat preservation and thermal protection field, especially in energy-saving and aerospace. [ABSTRACT FROM AUTHOR]

In this study, the WC doped W-Cu composites with high excellent thermal conductivity were fabricated by using coated composite powders combined with vacuum hot-pressure sintering. As-received W powders were pre-modified with organic additives via pyrolysis process (carburization process), and then Cu coated by electroless plating. The WC formed in situ doped W-Cu composite was obtained. X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques were used to characterize the composite powders and sintered composites. The results show that the structure of coated composite powders was W/C/Cu and the structure of sintered sample turned into W/WC/Cu. Both Cu matrix network and WC interfacial layer were obtained in the W-Cu composite. Compared with the W-20 wt%Cu composite without WC modification, the WC doped W-20 wt%Cu composite have excellent thermal conductivity (287.5 W/(m·K)), low coefficient of thermal expansion (4.40 ppm/k) and relatively high Vickers hardness (230.5 HV). The excellent properties are mainly because of Cu network structure formed and its interfacial layer WC yielding improved bonding between the W and Cu matrix. [ABSTRACT FROM AUTHOR]

Polyetherimide (PEI) is a high performance thermoplastic polymer that retains its properties at elevated and cryogenic temperatures. Nanofiller reinforced PEI used in aerospace structures will substantially reduce the payload. This study attempts to optimize nanofiller content and process parameter for melt compounding of PEI/acid ( COOH) functionalized MWCNTs (Multi-walled Carbon Nanotube) nanocomposite using Response surface methodology (RSM). Face Centered Central Composite Design (FCCD) with two factors viz. MWCNT content and extrusion screw speed at three levels each is used to model and optimize nanocomposite properties relevant to aerospace applications. FTIR spectrum confirmed the functionalization of MWCNTs while morphological analysis confirmed the dispersion of MWCNTs. COOH-MWCNTs reinforced composite showed enhanced thermal and mechanical properties along with better retention of properties upon exposure to gamma irradiation and atomic oxygen. These properties were modeled with non-linear quadratic equations using regression analysis and verified by validation experiments. Optimization for performance of nanocomposites for aerospace application has been revealed by overlapping the contour plots within the practical constraints to recognize the combination of factor ranges. [ABSTRACT FROM AUTHOR]

More effective approaches need to be developed for solving the aging and thermal stability problems of crumb rubber modified asphalt (CRMA). This paper focused on microwave and trans-polyoctenamer (TOR). Therefore, various CRMA were prepared by crumb rubber (CR), microwave irradiated CR, TOR and base asphalt. The samples were subjected to thin film oven test (TFOT), pressure aging vessel (PAV) and high temperature storage tests. The effects of microwave and TOR were evaluated by rheological, FTIR and SEM tests. The results showed that microwave activated CR increases the risk of fatigue cracking caused by hardening effect of aging but endows the aged residue with stronger resistance to thermal cracking. These results attribute to the degradation and de-vulcanization effect of microwave on CR (verified by FTIR). TOR activated CRMA displayed a more obvious hardening effect and the improved low temperature creep behavior after aging. TOR improves the compatibility and storage stability of CRMA. Double bonds in TOR participate in chemical reaction and benefit to stability, which are verified by the decreased intensity of peak at 966 cm − 1 . However, microwave treatment on CR has negative effect on stability of CRMA. Thermal stability was further verified by steady flow method. [ABSTRACT FROM AUTHOR]

The use of dispersions of poly(vinyl alcohol) PVA and detonation nanodiamond (DND) as novel inks for 3D printing of variously shaped objects using a layer-by-layer additive manufacturing method is reported. In parallel with the nanocomposites preparation, we designed a 3D printing apparatus and settled protocols for the shaping of hybrid materials, choosing PVA-DND inks as a model system to test the performances of the 3D apparatus. Along with material design and preparation, we discuss the main factors influencing the quality of the final printed objects and enlighten the importance of the matching between the chemical/physical properties of the materials to be extruded and the characteristics of the 3D printer. The thermal and mechanical properties of the printed systems have been tested by Differential Scanning Calorimetry and Contact Resonance Atomic Force Microscopy. The analysis of the mechanical properties of the 3D printed objects evidenced, for 0.5% w/w , 1% w and 5% w DND-loaded nanocomposites, values of mean indentation modulus that are 22%, 44% and 200% higher, respectively, than that of the unloaded PVA. The results of the present research, indicate that an appropriate methodology is able to print PVA-DND nanocomposites in well-defined and shaped structures, suitable for a variety of possible applications. [ABSTRACT FROM AUTHOR]

Electrochemical polishing (ECP) was used to improve surface quality of Inconel 718 components fabricated by selective laser melting (SLM). In this study, SLM Inconel 718 tube part surface was processed by electrochemical polishing by pre-optimized parameters. The surface morphology and roughness evolution with different electrochemical polishing duration were characterized by scanning electron microscopy (SEM) and 3D surface profilometer. The surface roughness can reach as low as 3.66 μm (Ra), compared with the initial surface roughness of 6.05 μm. Microstructure and XRD study indicated that the δ and carbide phase were revealed under ECP with long duration instead of γ phases on the original sample surface. In order to identify the mechanical properties of the surface, nano-indentation tests were carried out on both the original sample surface and the sample surface after ECP. The results showed that the samples after ECP possess a relatively lower surface hardness and surface elastic modulus. [ABSTRACT FROM AUTHOR]

[Display omitted] • A literature review on the heat and flow properties of lattice structures is performed, and design parameters are identified. • Detailed geometric modeling and clear the knowledge gaps in the flow and heat properties of various lattices. • The results are compared with the findings obtained from existing literature and documented in detailed charts. Lattice structures are known for their capability to be tailored for achieving specific properties such as high porosity and strength, impact energy absorption and lightweight. While the mechanical properties of the strut-based and surface-based lattice structures have already been investigated in the literature, a systematic investigation of their flow and thermal properties has yet to be established. This work investigates the friction factor and convective heat transfer coefficient across strut- and surface-based lattice structures. The modeled structures are simulated in the convective heat transfer environment to gather the heat transfer coefficient and the friction factor outputs. The simulation results are documented in this work and used to generate a flow and thermal property chart to support the design process by providing a guideline for selecting lattice topologies. [ABSTRACT FROM AUTHOR]

[Display omitted] • Importance of thermal/geometric features of composite structures to effective thermal conductivity is studied. • Effective thermal conductivity is correlated with the features using machine learning. • Using a machine learning model, composites are classified based on the existence of percolation path. • Volume fraction of particles and interface thermal resistance are most influential parameters on effective thermal conductivity. Data-driven thermal and percolation analyses are conducted to elucidate the effects of various characteristics on the effective thermal conductivity of complex 3D composite structures. These characteristics include the thermal and geometric properties of the composite constituents, the interface resistance, and the existence of percolation paths. A series of voxel-wise microstructure samples with various characteristics are generated. Their effective thermal conductivities are evaluated using a diffuse-interface-based computational homogenization method. A voxel-based algorithm is employed to identify the potential percolation paths in the structures. The homogenization results show particularly significant effects of the percolation path in composite samples with higher aspect ratios and interface resistances. The importance of different thermal and geometric features to the effective thermal conductivity is analyzed using a data-driven sensitivity study. The analysis also demonstrates that the particle volume fraction and interface thermal resistance are the most influential characteristics for determining the effective thermal conductivity. Finally, employing a surrogate-based classification model, microstructures with and without percolation can be distinguished with an accuracy of 93%. [ABSTRACT FROM AUTHOR]

The thermal properties of asphalt mixture play an important role in determining asphalt pavement temperature and accordingly viscoelastic pavement responses under vehicular loading. This paper aims to quantify the effect of thermal modified asphalt mixture on pavement responses and performance. A validated microstructure model of asphalt mixture was developed to predict thermal properties of asphalt mixtures with different thermal additives. The three-dimensional (3-D) finite element (FE) models were developed to predict temperature fields in the pavement structure and critical pavement responses under vehicular loading. The accuracy of the 3-D FE model was validated with field measurements. The critical responses in different thermal-modified pavement structures were analyzed. The long-term pavement performance including rutting and fatigue cracking were evaluated using the mechanistic-empirical analysis procedure. The analysis results show that using low-conductivity asphalt mixture in the surface course and high-conductivity asphalt mixture in the deeper layer decreased rutting effectively at high temperature and moderate temperature, but increased rutting slightly at low temperature. Using low-conductivity asphalt mixture in the pavement, especially in the upper layers could effectively improve the resistance to fatigue cracking at high temperature and moderate temperature, but slightly decrease the fatigue cracking resistance at low temperature. Finally, thermal-modified pavement structures that can improve both rutting and fatigue cracking resistance effectively were recommended. [ABSTRACT FROM AUTHOR]

A new ternary nanocomposite system containing polylactic acid, an organoclay and a hydrogel was designed and prepared by solution casting method. The hydrogel was synthesized from 2-acrylamido-2-methylpropane sulfonic acid (AMPS) and N , N ′-methylenebisacrylamide (MBA) via a radical polymerization in the presence of ammonium persulfate (APS). As a potential reinforcement, the hydrogel was used in a PLA system combined with and without a new organoclay. The organoclay was prepared from Cloisite Na + and protonated form of SABO®STAB UV 94 via an ion-exchange reaction. The morphology, mechanical, thermal and combustion properties of all the PLA systems were studied. In the presence of the organoclay, the hydrogel showed a synergistic effect on improving all the investigated properties of PLA. The temperature at 5 mass% loss (T 5 ) was increased from 308 °C to 325 °C in PLA/hydrogel-organoclay nanocomposite containing 3 mass% of each the hydrogel and organoclay (PSH 6) as compared to the neat PLA. The peak heat release rate was decreased from 567.3 W/g for PLA to 410.1 W/g for PSH 6. According to the mechanical tests results, as compared with the neat PLA, by adding both of the hydrogel and organoclay into PLA matrix, the tensile strength was increased from 43.7 to 64.4 MPa. [ABSTRACT FROM AUTHOR]

In this work, the W-(Ni)-Cu composites were fabricated by Selective Laser Melting with the different W content up to 80 wt.%. The effects of relative density, microstructure on thermal conductivity, thermal expansion coefficient, roughness and hardness of W-(Ni)-Cu composites were evaluated. The results indicate that during SLM W-(Ni)-Cu composites, there are two kinds of densification mechanism reflected on the microstructure characteristic. Rearrangement densification favors to achieve higher relative density, dense compact Cu matrix and a homogeneous distribution of W solids, the thermal conductivity closer to theoretical value. Solid-state sintering densification obtains porous Cu matrix with W-W contiguity and the phenomenon is severer with the increase of W content, the thermal conduction structure is in good agreement with Randall's model. Ni additive is beneficial to densify the Cu matrix. The obtained coefficient of thermal expansion (CTE) through two kinds of densification mechanism are both lower than the theoretical value. The results show that the thermal conductivity and CTE increase with the Cu content, while the relative density trends on the contrary. The surface morphology presents easy to balling due to the instinct property of W and Cu. The roughness and hardness also increase with the increase of W content. [ABSTRACT FROM AUTHOR]