查看更多>>摘要：? 2022 Elsevier B.V.Composite Cu2?xSe thin films can be rapidly prepared on brass by liquid chemical deposition in 1 min. With the addition of acetic acid in the oxidizing solution containing SeO2/H2SO4/ H2O2, the sizes of the selenide particles become smaller and thus much smoother films are obtained, while the films become thinner and denser as seen from their scanning electron microscopy and EDS results. X-ray diffraction and XPS results reveal that copper acetate is spontaneously formed with the acetate acid addition, and the existence of copper acetate hinders the growth of copper selenides, leading to the decrease in film thickness; during their mutual deposition, copper acetate probably fills the spaces among selenide particles, and thus improves the compactness and decrease the roughness of the composite film. The miniaturization of the selenide particles with the acetate acid addition results in a great improvement in both the hardness and wear resistance of the composite films. When the composite films are sealed by sodium silicate, a successive interlayer is formed on their outer surfaces that result in the further improvement in their corrosive resistance as reflected by the electrochemical test and thermal humidity test.
查看更多>>摘要：? 2022 Elsevier B.V.Thermoelectric (TE) materials have been extensively investigated to solve the energy crisis and alleviate environmental pollution. Currently, n-type and p-type Bi2Te3 based are the only commercialized TE materials. However, their application has been severely limited by the low TE figure of merit (ZT) of p-type Bi2Te3-based TE materials. Here, we demonstrate that the TE performance of p-type materials could be improved by incorporating Bi2Fe4O9 magnetic nanoparticles. Bi2Fe4O9 magnetic nanoparticles could effectively scatter low-energy carrier and improve the carrier quality. The synergistic effect of boundary scattering and magnetic particles scattering lead to the increase of Seebeck coefficient and decrease of thermal conductivity. Finally, the maximum ZT value 1.1 is obtained at 393 K, which is 13% higher the pure sample. The average ZT value of the nanocomposite consisting Bi2Fe4O9 magnetic nanoparticles is 0.98 in the temperature range of 303–483 K, exhibiting an increase of 11%. Overall, the results indicate that magnetic nanoparticles with low saturation magnetic moment have positive effect on the performance of TE materials.
查看更多>>摘要：? 2022 Elsevier B.V.Heterojunction materials composed of narrow and wide band-gap semiconductors possess different photoelectric responses under different wavelength incident light, and show distinct photogenerated charge carrier dynamics. In this work, taking the hydrothermal method fabricated CuO nanosheets / ZnO nanorods heterojunction materials as example, the wavelength dependent photoinduced charge carrier dynamics in this heterojunction material have been carefully studied. Transient surface photovoltage (TSPV) measurements reveal that the photogenerated holes gather at the surface of the fabricated CuO / ZnO with 355 nm light illumination, but photogenerated electrons gather at the surface under 532 nm light. Photocatalytic degradation experiments suggest that CuO / ZnO heterojunction material has better performance under ultraviolet light than that under visible light.
查看更多>>摘要：? 2022Samarium-cobalt sintered magnets offer excellent magnetic properties, thermal stability, and corrosion resistance. They are used in a variety of defense and civilian applications, especially when elevated operation temperatures (e.g., 200 oC to 550 oC) are required. However, the utilization of these materials is restricted by their brittleness. Improving their mechanical resilience would make them more cost-effective, efficient, and robust in decarbonization and other function-related applications while reducing the pressure on critical material supply chains. In this paper, we engineer a series of novel heterogeneous microstructures, such as laminated coarse grain (CG)/fine grain (FG) and core/shell CG/FG microstructures, to produce unprecedented combinations of superior mechanical and magnetic properties without altering the chemical compositions of the magnets or common heat treatment procedures. A 60% flexural strength enhancement is obtained using heterogeneous Sm2(CoFeCuZr)17 sintered magnets with little impact on their magnetic properties. The mechanically robust heterogeneous Sm-Co sintered magnets have a minor (e.g., less than 4.6%) reduction in the energy product (BH)max due to a slightly reduced squareness of the demagnetization curve, with no decrease in either the remanence (Br) or the intrinsic coercivity (Hci). The flexural strengths of these heterogeneous Sm-Co magnets depend on the volume ratios and mean grain sizes of the FG/CG regions, as well as their microstructural architectures. The fine-grained regions act as mechanical strengthening sites, which can be strategically used when designing the magnet for different applications. This technology is highly compatible with existing magnet manufacturing processes and thus can be adopted readily by the magnet industry.
查看更多>>摘要：? 2022 The Author(s)Microstructure and texture evolution during high-pressure torsion (HPT) of a novel Mn-added CoCrNi medium entropy alloy (Co33Ni33Cr19Mn15) is investigated for the first time. The alloy exhibited a rapid rise in hardness at relatively low shear strains (γ≤20). It is attributed to an extensive dislocation activity to achieve saturation in dislocation density of ~1016 m?2, combined TWIP and TRIP effects and microstructural refinement. At higher shear strain, hardness increased at much reduced rates owing to saturation of dislocation density, twin fault probability and the TRIP effect, besides continued grain refinement for severe nano-structuring led to subsequent strengthening. The FCC phase showed remarkable stability except a small degree of initial deformation-induced HCP martensitic transformation in an early stage of HPT. The ideal shear texture components were observed at low shear strain, and these continued to evolve up to 5 turns of HPT processing. For similar HPT processing conditions, the studied alloy showed superior hardness (~650 Hv) compared to a wide spectrum of FCC materials, which is ascribed to a combination of the strengthening mechanisms of Taylor hardening, the TRIP and TWIP effects and Hall-Petch strengthening resulting from the nano-structured grains having an average size of ~35 nm.
查看更多>>摘要：? 2022 Elsevier B.V.The effect of tensile straining on the precipitation and dislocation behavior of the over-aged 7075 aluminum alloy at T7352 temper have been investigated. Microstructures depict dissolution of the precipitates at low tensile straining but reprecipitation occurs at a higher amount of strain. Such precipitation improves the resistance against stress-corrosion cracking as well as other mechanical properties. Detailed characterization displayed the formation of dislocation loops, forest dislocation along with tangled dislocations at a low amount of straining corresponding to a true strain of ~0.02. In contrast, low-density, high-density Taylor lattices, and dislocation cell structures were seen at higher true straining of 0.06, and 0.1 respectively. Dissolution, reprecipitation of second phases, changes in orientation, and development of dislocation structures are contributing to the two-slope deformation behavior of AA7075T7352 alloy.
查看更多>>摘要：? 2022 Elsevier B.V.Directed energy deposition (DED), a typical additive manufacturing technology, is now regarded as a promising technique to further improve the performance of single-crystal (SX) superalloys by minimizing chemical segregation. The multi-track overlapping deposition is an effective way to increase the three-dimensional size of the component, which provides the opportunity to fabricate large-size SX parts. However, more serious uneven thermal processes and stress concentration are also introduced by the track overlapping, which may pose challenges to the SX structural homogenization and stability during heat treatment. This investigation aims to reveal the microstructural evolution of multi-track overlapped nickel-based SX by DED during heat treatment. In this study, the effects of solution annealing (1290 °C /4 h), primary aging annealing (1150 °C /4 h), and secondary aging annealing (870 °C /8 and 14 h) on the microstructural evolution of a multi-track SX block fabricated via DED are investigated. Compared with conventional solution annealing, direct primary aging is more appropriate for the first-step treatment of DED multi-track SXs. Both the eutectic γ–γ' and strain concentration disappeared, whereas no excess carbides appeared after the primary aging process. The recrystallization is accompanied by the reduction of strain concentration during both solution annealing and primary aging, as detected via electron back-scattered diffraction. After 14 h of secondary aging annealing, relatively uniform size distribution of γ' precipitates is obtained. The present study demonstrates the microstructural evolution during the heat treatment of multi-track SX components and provides a basis for the further optimization of the heat treatment process.
查看更多>>摘要：? 2022 Elsevier B.V.Infrared nonlinear optical (NLO) materials with great laser conversion efficient play a key role in military and civil fields. SrZnSnSe4 was synthesized via replacing S elements with Se in SrZnSnS4 compound. SrZnSnSe4 crystallizes a two-dimensional layered structure with nearly parallel alignment of anionic groups [ZnSe4] and [SnSe4]. The experimental results show that the second harmonic generation (SHG) is about 5 times of AgGaS2, and the band gap of SrZnSnSe4 is 1.82 eV by direct measured method. In combination with theoretical calculation, the SHG coefficients of SrZnSnSe4 is d33 = 30.03 pm/V, and the birefringence is 0.290 at incident laser of 1240 nm, which can contribute to phase matching. These evidences show that SrZnSnSe4 can balance well among band gap, frequency doubling effect and birefringence, therefore, it is an excellent candidate for infrared NLO materials.
查看更多>>摘要：? 2022 Elsevier B.V.Microstructure and texture formations were investigated in a coarse-grained starting material (average grain size ~100 μm) of equiatomic CoCrNi MEA after severe warm-rolling and annealing. The results were compared with a fine-grained starting material (FGSM with average grain size ~7 μm) to highlight the effect of starting grain size. Progressive microstructural evolution accompanied by deformation bands, shear bands, and nano-twins formation resulted in an ultrafine microstructure in the heavily warm-rolled CGSM. The hardness of CGSM after 90% warm-rolling was similar to FGSM, indicating a rather comparable ultrafine microstructure. The deformation texture of the CGSM was rather similar to the FGSM featured by a weak brass component. Remarkably, the annealed grain sizes of the CGSM and FGSM series of specimens were rather similar. These observations amply corroborated with comparable deformation microstructure in the two materials. Both CGSM and FGSM showed weak recrystallization texture featured by the retention of deformation texture components. The results indicated rather limited effect of the starting grain size on microstructure and texture formation in warm-rolled and annealed CoCrNi MEA. Further, a remarkable strength-ductility balance could be obtained in annealed CGSM due to ultrafine microstructure and solid solution strengthening.
查看更多>>摘要：? 2022 Elsevier B.V.Effects of heat treatment conditions on the microstructure evolution, phase transformation and mechanical properties of dual phase Cu-Zn alloy were systematically investigated. Meanwhile, the relationship between the nano-hardness and the macroscopic hardness was also discussed in the study. The results show that the β phase rich in Zn, has the phase transformation temperature from 456.5 °C to 827.1 °C. With the increasing of heat treatment temperature, significant (200) (220) α phase to (200) (211) β phase transformation occur and the β phase fraction increases from as-received 13.1–41.3%. The grain becomes coarser and grows rapidly from 32.6 μm to 49.7 μm from temperature 550 °C to 800 °C, the increase of β phase results in the strength increases and the fracture elongation decreases. The β phase fraction has not varied significantly at temperature 750 °C and 800 °C, the strength has a further increase which is mainly attributed to a part of fine needles of Widmanst?tten phase begin to form. At the same displacement, the β phase exhibits a much larger load than that of the α phase, the material pile-ups around indent edges of the α phase becomes more evident indicating that the α phase is softer and has a better ductile. The big difference in the predicted hardness and the macroscopic hardness when heat treatment at 750 °C and 800 °C is mainly attributed to the formation of the fine needles of Widmanst?tten phase.
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