Journal of Materials Science最新文献

The growing demand for sustainable and high-performance materials has led to the exploration of natural fiber-reinforced composites. However, the optimal manufacturing techniques for enhancing their mechanical and thermal properties are still under-explored. The present study addresses this gap by utilizing microwave-based processing at 2.45 GHz to fabricate hybrid composites of linear low-density polyethylene (LLDPE) reinforced with sisal and banana fibers. The thermo-mechanical characterization was used to explore the performance of the various fabricated samples, such as LLDPE, sisal/sisal, banana/banana, and sisal/banana composite laminates. FTIR analysis was performed to study interfacial interactions within composites. The sisal/banana hybrid composite laminates demonstrated impressive properties with an Archimedes density of 0.9684 g/cc and exhibited superior mechanical and dynamic properties. Specifically, the sisal/banana hybrid composite had the highest tensile strength, flexural strength, and impact strength of 22.82 MPa, 15.87 MPa, and 254.35 J/m, respectively. Additionally, it had a storage modulus of 851.1 MPa. The Cole–Cole plot illustrated the heterogeneity within the composites, highlighting the strong interfacial adhesion between the fiber and the matrix. The fracture analysis of specimens shows that almost all specimens exhibit failure at the top location, likely due to the progressive formation of a structural feature known as a chap. Scanning electron microscopy analysis of fractured surfaces shows that fiber pullout, voids, and broken fibers are the common failure modes.

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This study investigates the morphology and composition of hydrides in Optimized ZIRLO following electrochemical deuterium charging. Both ZrO and ZrD_x phases were formed upon charging. The interfaces between these phases are investigated by using atom probe tomography aided by cryogenic sample transfer. The Ga and Sn have formed a “net”-like structure at the original atom probe specimen surface, which is assumed to be associated with the boundaries between individual hydride laths/needles, as it thought to have formed as these species were excluded from the hydrides. Calculation of the D/Zr ratio throughout the sample allows for identification of the ZrD_x phases, revealing the specimen consists of a complex arrangement of different hydride phases. In some areas there is small excess of D in the hydride, i.e. ZrD_2+y. This result is interpreted as deuterium which was “frozen” as it was passing through the hydride during electrochemical charging. The observed microstructural changes and interfacial phenomena contribute valuable insights that may prove useful for improving the performance and safety of Zr alloys.

The thin film thermoelectric (TE) materials with higher values of the figure of merit are of special interest due to their promising applications. In this regard, metal oxide thin films are introducing flexible and stretchable devices, a type of next-generation electronic gadgets, and hence possess the potential for TE applications at high temperatures and in novel devices. The mobility, concentration, and scattering of carriers in metal oxide and thin films determine the thermoelectric properties of the materials. The carrier properties can be changed by doping and precise methods of processing, which are not always straightforward. There are, therefore, still many challenges and opportunities to further improve their TE performance and device integration. Future research directions may include exploring new materials and structures, optimizing the doping and fabrication conditions, understanding the transport mechanisms and interfacial effects, and developing scalable and reliable TE devices. In this work, we first introduce the foundation of metal oxide and metal oxide-based TE materials, briefly describe their syntheses, and finally discuss their application underlining the challenges and opportunities.

To understand and further improve the corrosion resistance of a medium electroless phosphorus nickel coating (9 wt% P) under high-temperature and corrosive conditions, the microstructural evolution of the coating after various treatments, including thermal and mechanical methods (such as Hammer Peening), was extensively studied. Complementary analytical techniques, including SEM, EDS, in situ and ex situ XRD, and micro-indentation, were employed for detailed analysis. The transformation of the deposit from its amorphous state to a distinct structure comprising Ni, Ni₃P, and NiO due to thermal treatment (ranging from 20 to 800 °C) was examined. The evolution of microstructure with temperature and annealing duration was discussed, correlating with alterations in mechanical properties, particularly micro-hardness. At temperatures exceeding 310 °C, a phase transition occurred, characterized by co-precipitation of Ni and Ni₃P, leading to a significant change in the coating's mechanical behavior. With further temperature elevation, nickel diffused toward the surface, initiating NiO formation at 500 °C. The coating's oxidation behavior during isothermal treatment at varied temperatures (up to 800 °C) was also explored. This investigation was supported by thermodynamic calculations. Additionally, simplified kinetic simulations with the Dictra module from Thermo-Calc were proven to be able to reproduce the oxidation behavior. Hammer peening treatment enhanced the coating's hardness in its as-deposited state by introducing residual stresses that affected the precipitation kinetics during subsequent heat treatment. However, this hardening effect was no longer evident after the thermal treatment.

With the growing demand for personalized and high-quality jewelry, the jewelry industry is continuously innovating to meet consumer needs. A new type of amethyst, called lavender amethyst, has emerged in the market in recent years. However, limited research has been conducted on this crystal, leaving gaps in our understanding of its gemological features, optical effects, source, and artificial refinement methods. The milky texture is the primary distinguishing feature of lavender amethyst. This study reveals that the milky appearance of lavender amethyst is caused by light scattering from silica spherules ranging from 20 to 50 nm in size. These spherules form during the recrystallization process near crystal defects, gradually accumulating silica and leaching onto larger defects during heat treatment. It is determined that existing lavender amethyst has been artificially optimized, with precise control of treatment temperature and heating time to achieve the desired milky white gradient. Effective transformation into lavender amethyst requires amethyst with sufficient crystal defects, exhibiting specific absorption peaks in the low-temperature infrared spectrum. This study provides a comprehensive analysis of the gemological features, optical effects, and artificial refinement of lavender amethyst, shedding light on its hazy appearance and offering insights for optimizing and controlling similar gem crystal structures.

Cold-finished carbon steel bars were bonded by means of the transient liquid phase bonding (TLPB) process using amorphous metallic foils of the eutectic Fe-B composition as filler material. A homogeneous microstructure throughout the joint was obtained. Traces of borides in the middle of the joint were the only distinguishable microconstituent from the base metal due to the TLPB process. The B concentration profile across the joint was measured by neutron radiography and was found to be composed of a central sharp peak with a maximum concentration of 15.9 ppm B superimposed over a broad peak (base width of ≈ 5 mm) with a maximum concentration of 13.3 ppm B. Owing to this low range of B concentrations, boride precipitation was almost suppressed, and only a scarce number of borides were observed at the joint. The resulting boride structure was identified as Fe₂₃B₆ by synchrotron microfocused X-ray diffraction, and its stabilization at room temperature is discussed. The bonded samples were subjected to a bend test, with a bending angle of 180°, and no cracks were observed. In tension tests, the bonded samples attained an ultimate tensile strength (UTS) of 434 MPa, an elongation of 32.3% and a reduction area q of 51.2%—78.6%, 165.6% and 75.4%, respectively, of the base metal. The fracture of the bonded samples occurred at the joint. It was determined that the decrease in UTS compared with that of the base metal was due to the recovery, recrystallization and grain growth that occurred during the TLPB thermal cycle. In addition, from fracture surface observation, it was found that the decrease in q in bonded samples was caused by the presence of traces of borides at the joint, which were the result of the liquid phase that solidified during the cooling stage.

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The complex microstructure evolution and heterogeneities in metal additive manufacturing (AM) continue to delay the adoption of AM parts by additional industries. Achieving uniform and superior properties in AM parts requires better fundamental understanding of the microstructural evolution. A suitable pathway to gain such understanding is via in situ techniques such as high-speed X-ray imaging, high-resolution infrared cameras, or via synchrotron and neutron diffraction. However, these methods are complex and resource intensive. Modeling may be a more economical avenue, yet, to make these models more robust and reliable, data from in situ techniques are often required. We believe that in some cases, physical simulation methods originally developed for research on conventional processing such as forging, rolling, and welding may provide similar insights. This viewpoint article discusses existing experimental methods for tracking the microstructure evolution during AM in lab-scale settings, focusing on Ni-based superalloys as a case study. The proposed physical simulation methods include the Gleeble thermo-mechanical simulator, dilatometry, and the arc-melting heat treatment technique. These methods can also be integrated into various X-ray, synchrotron, and neutron diffraction set-ups. We discuss how insights derived from thermo-kinetic modeling can underpin the experimental observations from physical simulations. Last, in situ transmission electron microscopy is evaluated as a powerful method with unparalleled resolution for observing the microstructure evolution directly during simulated AM processes. We believe that these methods can be extended to other alloy systems, enhancing scientific understanding, and streamlining the efficient development of AM parts with superior and more uniform properties, promoting the more widespread adoption of AM.

Nowadays, Alkaline earth metal halofluoride, as part of layered materials, have drawn considerable interest for applications in optoelectronic devices and sensors, benefiting from wide bandgap properties. In this work, the monolayer alkaline earth metal halofluoride XYF (X = Ca/Sr/Ba, Y = Cl/Br/I) were investigated based on first-principles calculations. These monolayers can be exfoliated with energies comparable to conventional two-dimensional (2D) materials, suggesting their potential for practical applications. Additionally, XYF monolayers all exhibit excellent structural stability, with a maximum elastic modulus ranging from 37.144 to 76.829 N/m, indicating significant flexibility. More strikingly, these materials are characterized as ultra-wide bandgap (UWBG) semiconductors, with direct bandgaps spanning from 5.06 to 7.56 eV using HSE06 functional. Furthermore, exploration was conducted into introducing magnetism by doping of S and P atoms, thereby providing magnetic moments in non-magnetic systems. Our research broadens the spectrum of 2D wide-bandgap materials, and holds promise for their applications in optoelectronics, flexible electronics and spintronics.

Advanced thermal management materials play a crucial role in driving innovation and enhancing the performance of cutting-edge technologies. In this work, polyimide foams were fabricated by freeze-drying precursor polyamic acid (PAA) solutions and thermally imidization, incorporating π-electron-rich benzimidazole structures along with Cu²⁺, Ca²⁺, Na⁺, and K⁺ ions to form cation-π crosslinked structures. The integration of cation-π crosslinked structures notably enhanced polyimide foams, boosting its compressive strength, glass transition temperature, and thermal insulation properties. Particularly noteworthy was the superior enhancement and modification effects exhibited by Ca²⁺ among the cations, followed by Cu²⁺, whereas Na⁺ and K⁺ showed relatively lesser effectiveness. Specifically, the inclusion of 30 mol% Ca²⁺ resulted in a remarkable 136.36% increase in compressive strength and a 320.47% increase in Young's modulus for the polyimide foams. Furthermore, a 50 mol% infusion of Ca²⁺ reduced the thermal conductivity from 0.0533 to 0.0432 W m⁻¹ K⁻¹ compared to pristine polyimide foam, while also decreasing the surface temperature of a 15 mm thick sample from 74.1 to 55.7 °C after exposure to a 200 °C platform for 10 min. This study underscores the importance of integrating cation-π crosslinked structures into polyimide foams, leading to significant improvements in thermal insulation properties and thus advancing the field of thermal management materials.

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