Search Results (21)

Researches were conducted on the laser welding of 3 mm sheet-thickness lap joints of AA5052 with ER4043 filler wires. The effects of laser power on the joint morphology, microstructure, mechanical properties, and corrosion resistance were investigated. The results indicate that both increased heat input and the addition of filler wires make the molten pool more instable, which results in more process pores. Circular pores are observed in the upper part of the weld, while chain-like pores are distributed in the middle of the weld. The highest tensile strength of the weld joint is 192.61 MPa with an elongation of 10.1% at a laser power of 3.5 kW. The microhardness at the center of the weld is approximately 25% higher than the base material, which is probably because the addition of ER4043 filler wires brings more Si element to the weld. Moreover, the weld joints display superior corrosion resistance compared to the base material. These outcomes enhance the understanding of AA5052 laser welding with fillers wire and provide valuable in-sights for engineering applications. Full article

With the miniaturization of current electronic products, ceramic/polymer composites with excellent thermal conductivity have become of increasing interest. Traditionally, higher filler fractions are required to obtain a high thermal conductivity, but this leads to a decrease in the mechanical properties of the composites and increases the cost. In this study, silicon nitride nanowires (Si₃N₄NWs) with high aspect ratios were successfully prepared by a modified carbothermal reduction method, which was further combined with AlN particles to prepare the epoxy-based composites. The results showed that the Si₃N₄NWs were beneficial for constructing a continuous thermal conductive pathway as a connecting bridge. On this basis, an aligned three-dimensional skeleton was constructed by the ice template method, which further favored improving the thermal conductivity of the composites. When the mass fraction of Si₃N₄NWs added was 1.5 wt% and the mass fraction of AlN was 65 wt%, the composites prepared by ice templates reached a thermal conductivity of 1.64 W·m⁻¹·K⁻¹, which was ~ 720% of the thermal conductivity of the pure EP (0.2 W·m⁻¹·K⁻¹). The enhancement effect of Si₃N₄NWs and directional filler skeletons on the composite thermal conductivity were further demonstrated through the actual heat transfer process and finite element simulations. Furthermore, the thermal stability and mechanical properties of the composites were also improved by the introduction of Si₃N₄NWs, suggesting that prepared composites exhibit broad prospects in the field of thermal management. Full article

As a sustainable substitute for non-renewable mineral resources and solid waste landfilling, municipal solid waste incineration residues (MSWIRs) are useful in road pavements. This study investigates the thermal characteristics and temperature distribution of flexible pavements containing MSWIRs with hollow microsphere structures. First, the volumetric properties of asphalt mixtures containing MSWIR fillers were measured. The effects of MSWIRs on the mixture’s physical characteristics were investigated in terms of thermal conductivity, specific heat capacity, and thermal diffusivity. A three-dimensional finite element model incorporating surface thermal conditions was established and validated to analyze the internal temperature distribution and heat transfer behavior within the asphalt. Finally, the high-temperature conditions of summer were simulated in an indoor irradiation test to evaluate the risk of heat islands in urban areas. The results showed that the mixture containing MSWIRs exhibited a higher specific heat capacity (from 0.8385 to 0.9554 J/(kg·K)) and lower thermal conductivity (from 1.4356 to 1.1362 W/(m·K)) than the reference mixture with limestone filler. Therefore, it contributed to a lower heat flux distribution within the pavement. However, the increase in asphalt surface temperature caused by MSWIRs may exacerbate the urban heat island effect in the summer, which should be considered before using road materials containing MSWIRs. Full article

With the rapid development of the electronics industry, there is a growing demand for packaging materials that possess both high thermal conductivity (TC) and low electrical conductivity (EC). However, traditional insulating fillers such as boron nitride, aluminum nitride, and alumina (Al₂O₃) have relatively low intrinsic TC. When graphene, which exhibits both superhigh TC and EC, is used as a filler to fill epoxy resin, the TC of blends can be much higher than that of blends containing more traditional fillers. However, the high EC of graphene limits its application in cases where electrical insulation is required. To address this challenge, a method for coating graphene sheets with an in situ grown Al₂O₃ layer has been proposed for the fabrication of epoxy-based composites with both high TC and low EC. In the presence of a cationic surfactant, a dense Al₂O₃ layer with a network structure can be formed on the surface of graphene sheets. When the total content of Al₂O₃ and graphene mixed filler reached 30 wt%, the TC of the epoxy composite reached 0.97 W m⁻¹ K⁻¹, while the EC remained above 10¹¹ Ω·cm. Finite element simulations accurately predicted TC and EC values in accordance with experimental results. This material, with its combination of high TC and good insulation properties, exhibits excellent potential for microelectronic packaging applications. Full article

In the present paper, we report polymer composites based on phenolic resin filled with hexagonal boron nitride; hot compression molding coupled with solution-based mixing were used to manufacture the composites. The paper presents experimental results on the physical and physicochemical properties of the obtained composites: thermal stability in air and argon, dielectric constant and dielectric loss tangent, active electrical resistance, thermal conductivity (mean and anisotropy), and mechanical strength. It is shown that the proposed technique of composite manufacturing, including the application of high-process pressures, makes it possible to obtain materials with high anisotropy of thermal conductivity, extremely high-filler content, and excellent dielectric properties, all of which are very important for prospective highly efficient lightweight heatsink elements for electronic devices. Experimental values of thermal conductivity and dielectric constant were analyzed using known mathematical models. Experimental values for thermal conductivities (up to 18.5 W·m⁻¹·K⁻¹) of composites at filler loadings of 65–85 vol.% are significantly higher than published data for bulk boron nitride/polymer composites. Full article

Conventional radiation-shielding composites usually contain lead, which results in high toxicity and poor portability. Tungsten (W) is an ideal radiation-shielding element that can replace lead due to its high atomic number and non-toxicity. In this work, radiation-shielding composites were prepared using natural rubber (NR) as a matrix and three different particle size powders, namely W, WO₃ and WC, as fillers. The results show that, for X-rays, the linear attenuation coefficient of radiation-shielding composites based on natural rubber containing WC with a particle size of 50 μm (50 WC/NR) is 27.005 cm⁻¹ at an X-ray tube voltage of 40 kV, which is more than 14 times the linear attenuation coefficient of NR. For γ-rays, a linear attenuation coefficient of 50 WC/NR achieves 8.320 cm⁻¹ at 81 keV, which is over 55 times the linear attenuation coefficient of NR. In addition, 50 WC/NR had the highest elongation at break at 548.989% and had the lowest hardness at 62 HA. In summary, 50 WC/NR can be used as an alternative to traditional radiation-shielding materials containing lead and has wide application prospects. Full article

A series of finite element analyses were conducted to clarify the effect of contact and interfacial resistance between constituents on effective thermal conductivities of dispersed composites. Equally dispersed fillers in FCC (face-centered cubic) and BCC (body-centered cubic) material systems were extracted from cyclic microstructures as unit cell models. In addition to spherical fillers, a polyhedron called the Wigner–Seitz cell that can realize a fully packed microstructure was chosen as the shape of the filler to investigate the effect of contact between the high volumetric fraction of fillers. The effective thermal conductivities of the resulting composites were calculated based on the FEA results and compared to the theoretical results for various volume fractions of the fillers including the maximum packing fraction. The following conclusions were obtained from the present study: 1. The effect of the contact depending on the shape and configuration of the fillers has more of a significant influence on the effective thermal conductivity than the influence of the increase in the volume fraction of the fillers. 2. When the contact occurred, the effective thermal conductivity became more than double that without contact. 3. Interfacial thermal resistance must be less than the order of 10⁻⁴ m² K/W to obtain improvement in the effective thermal conductivity by compounding the fillers. Full article

This research reports on Vis- and solar-active photocatalytic bi-layered films of TiO₂ (layer 1) and a composite with TiO₂ matrix and graphene oxide or reduced graphene oxide filler (layer 2) obtained by coupling two methods: spray pyrolysis deposition followed by spraying a diluted sol. The thin films crystallinity degree, surface morphology and elemental composition were recorded and the composites were tested in photo-degradation processes, using the standard 10 ppm methylene blue solution, under simulated UV + VIS irradiation conditions using an irradiance measured to be close to the natural one, in continuous flow process, at demonstrator scale; these results were compared with those recorded when using low irradiance values in static regime. The effect of the increase in the graphene oxide content was investigated in the concentration range 1.4%_w...10%_w and was found to increase the process efficiency. However, the photocatalytic efficiencies increased only by 15% at high irradiance values compared with the values recorded at low irradiance as result of the electron-hole recombination in the composite-thin film. Similar experiments were run using composites having reduced graphene oxide as filler. The interfaces developed between the matrix and the filler were discussed outlining the influence of the filler’s polarity. The thin films stability in aqueous medium was good, confirmed by the results that outlined no significant differences in the surface aspect after three successive photocatalytic cycles. Full article

Laser welding-brazing was used to join cemented carbide WC-Co and steel dissimilar materials. In this study, high-speed welding was adopted. The effect of welding parameters and brazing filler metals on the macrostructure, elemental diffusion, micro hardness and thermomechanical behavior was analyzed using optical metallography, scanning electron microscopy, electron probe micro-analysis, hardness test, and finite element method (FEM) based on thermo-elastic-plastic analysis. The experimental results show that increasing laser power is helpful to the increase of maximum welding speed. However, FEM also shows that increased welding speed leads to residual stress concentration, especial in the vicinity of jig. It is still a challenge to optimize laser power welding speed for a given brazing filler metal. The results show: when using pure copper, silver and nickel (thickness is less than 0.5 mm) as brazing filler metal, the combination, laser power of 1.2 kW and welding speed at 0.1 m/s, leads to complete penetration with good weld formation. However, when using Cu/Invar/Ni as brazing filler metal, laser power should increase to 1.7 kW if we still using a higher welding speed (0.1 m/s). Although a trial of high speed welding in laser welding-brazing exhibits feasibility, as-welded joints still have much more brittle risks due to the higher residual stresses. Full article

All solid-state room-temperature lithium-sulfur (Li-S) batteries have gained increasing attention due to their ability to eliminate the polysulfides shuttle effects and the safety dangers associated with the liquid electrolytes. Herein, a novel composite solid-state electrolyte, which is nickel-tungsten carbides (NiWC) over mesoporous silica (SBA-15) filled polyethylene oxide (PEO), was developed and investigated for Li-S batteries. The filler minimizes the crystallinity of the PEO and increases the ionic conductivity of the electrolyte, resulting in lowering the AC impedance of electrolyte composite from 26,256 ohm to 2416 ohm and to 5734 ohm after adding the electrolyte material with Ni/W ratios of 1:1 and 9:1, respectively. A high initial specific capacity of 1305 mAh g⁻¹ and a capacity retention of 66.7% after 8 cycles at C/10 was obtained at room temperature after adding NiWC/SBA-15 with a Ni/W ratio of 1:1. This novel composite solid-state electrolyte shows a remarkable long-term performance at high current rates (1, 2, 4, and 5C) and rate capabilities at 0.1, 0.2, 0.5, 1, 2, 4 and back to 0.1C. The battery was able to recover 77% of the initial specific capacity at 0.1C. The materials were characterized by XRD and SEM-EDX to study the crystallinity and elemental distributions, respectively. Full article

Si₃N₄ ceramics with a microscale rice leaf structure (MRLS) and titanium alloy were connected via brazing, and the influence of the surface microstructure on the ceramic connection was analyzed. MRLS fabrication is an efficient and high-degree-of-freedom method that can be used to change a material’s surface morphology and wettability. The MRLS was obtained at a laser power of 110 W, with line spacings of 100 and 50 μm. The laser-treated surface included nanoparticles and micro particles, exhibiting a coral-like structure after agglomeration. When the MRLS was used to braze the titanium alloy, no defects were observed at the brazing interface, and the formation was excellent. Throughout the brazed joint, the MRLS remained intact and formed a strong metallurgical bond with the brazing filler metal. A finite element analysis was performed to study the cross-sectional morphology after joint fracture; from the load-time curve, it was found that the MRLS on the surface not only helped improve the mechanical occlusion and brazing area at the interface, but also helped generate compressive stress on the Si₃N₄ side. Crack propagation was hindered, thereby increasing the joint strength. Full article

The thermal insulation effect of the coating was closely related to the content of the thermal insulation filler, but too much filler would cause interfacial compatibility problems of various substances in the coating, micro-defects in the coating, and affect the anti–corrosion performance of the coating. Therefore, solving the interface problem was the key to preparing a coating with heat insulation and anticorrosion functions. In this study, organic–inorganic hybrid polymer was used to modify the surface of vacuum ceramic microbeads, and epoxy–silicone resin was used as the film–forming material to prepare a heat-insulating and anticorrosive coating that can withstand 200 °C. The SEM morphology showed that the interface compatibility of the vacuum ceramic beads modified by the organic–inorganic hybrid agent and the film-forming material were improved, the dispersibility was significantly improved, and the beads were tightly arranged; the thermal conductivity of the coating reached 0.1587 W/(m·K), which decreased by 50% after adding 20% ceramic beads, ANSYS finite element simulation showed that the coating has good thermal insulation performance; after the coating underwent a thermal aging test at 200 °C for 600 h, the microstructure was dense, and the low-frequency impedance modulus was still around 10⁹ Ω·cm². There was no obvious defect in the microstructure after the alternating cold and heat test for 600 h; the low-frequency impedance modulus was still above 10⁸ Ω·cm², and the low-frequency impedance modulus of the coating was 10¹⁰ Ω·cm² after the 130d immersion test, indicating that the coating had good heat resistance and anti-corrosion performance. Full article

In this paper, a novel approach to obtain a ferromagnetic material for smart applications was implied. A combination of mechanical alloying (MA) and plasma spheroidization (PS) was applied to produce Ni₃₆Al₂₇Co₃₇ spherical powder. Then its structure was systematically studied. It was shown that homogenization of the structure occurs due to mechanism of layered structure formation. The dependence of the lamella thickness on the energy dose input at MA was defined. It was found that 14.7 W⋅h/g is sufficient to obtain lamella thickness of 1 μm and less. The low-energy mode of a planetary mill with rotation speeds of the main disk/bowl of 150/−300 rpm makes it possible to achieve a uniform element distribution upon a minimal amount of impurity. During MA in an attritor Ni₃Al-type intermetallic compounds are formed that result in more intensive degradation in particle size. Plasma spheroidization of the powder after MA allowed obtaining Ni₃₆Al₂₇Co₃₇ spherical powder. The powder had a fine β + γ-structure. The particle size distribution remains almost unchanged compared to the MA stage. Coercivity of the powder is 79 Oe. The powder obtained meets the requirements of selective laser melting technology, but also can be utilized as a functional filler in various magnetic composites. Full article

Thermal interface materials (TIMs), typically composed of a polymer matrix with good wetting properties and thermally conductive fillers, are applied to the interfaces of mating components to reduce the interfacial thermal resistance. As a filler material, silver has been extensively studied because of its high intrinsic thermal conductivity. However, the high cost of silver and its toxicity has hindered the wide application of silver-based TIMs. Copper is an earth-abundant element and essential micronutrient for humans. In this paper, we present a copper-based multi-dimensional filler composed of three-dimensional microscale copper flakes, one-dimensional multi-walled carbon nanotubes (MWCNTs), and zero-dimensional copper nanoparticles (Cu NPs) to create a safe and low-cost TIM with a high thermal conductivity. Cu NPs synthesized by microwave irradiation of a precursor solution were bound to MWCNTs and mixed with copper flakes and polyimide matrix to obtain a TIM paste, which was stable even in a high-temperature environment. The cross-plane thermal conductivity of the copper-based TIM was 36 W/m/K. Owing to its high thermal conductivity and low cost, the copper-based TIM could be an industrially useful heat-dissipating material in the future. Full article

For aerospace applications, honeycomb sandwich panels may have small perforations on the cell walls of the honeycomb core to equilibrate the internal core pressure with external gas pressure, which prevent face-sheet/core debonding due to pressure build-up at high temperature. We propose a new form of perforation on the cell walls of honeycomb sandwich panels to reduce the influence of the perforations on the cell walls on the mechanical properties. In this paper, the high temperature mechanical properties of a new vented Ti-6Al-4V honeycomb sandwich panel were investigated. A vented Ti-6AL-4V honeycomb sandwich panel with 35Ti-35Zr-15Cu-15Ni as the filler alloy was manufactured by high-temperature brazing. The element distribution of the brazed joints was examined by means of SEM (scanning electron microscopy) and EDS (energy-dispersive spectroscopy) analyses. Compared to the interaction between the face-sheets and the brazing filler, the diffusion and reaction between the honeycomb core and the brazing filler were stronger. The flatwise compression and flexural mechanical properties of the vented honeycomb sandwich panels were investigated at 20, 160, 300, and 440 °C, respectively. The flatwise compression strength, elastic modulus, and the flexural strength of the vented honeycomb sandwich panels decreased with the increase of temperature. Moreover, the flexural strength of the L-direction sandwich panels was larger than that of the W-direction sandwich panels at the same temperature. More importantly, the vented honeycomb sandwich panels exhibited good compression performance similar to the unvented honeycomb sandwich panels, and the open holes on the cell walls have no negative effect on the compression performance of the honeycomb sandwich panels in these conditions. The damage morphology observed by SEM revealed that the face-sheets and the brazing zone show ductile and brittle fracture behaviors, respectively. Full article