查看更多>>摘要：To reveal the state and effect of oxygen on high entropy alloys (HEAs) prepared by powder metallurgy, a VNbMoTaW refractory HEA was prepared by mechanical alloying and vacuum hot-pressing sintering. During mechanical alloying, with increasing ball milling time, the elemental distribution of the VNbMoTaW powders gradually became homogeneous, and the particle size decreased, while ~0.2 atom% O was introduced. After sintering at 1700 °C and 40 MPa for 2 h, a Ta-rich oxide with a grain size of approximately 15 nm was formed, leading to brittle fracture of the sintered VNbMoTaW HEA. When the sintering temperature was increased to 1900 °C, the grain size of the oxides decreased to ~8 nm and was dispersed on the BCC solid solution matrix. The yield strength of the VNbMoTaW HEA at room temperature and 1600 °C reached 2800 MPa and 350 MPa, respectively, due to Orowan strengthening caused by dispersed nano-sized oxides; additionally, the plasticity deformations at room temperature were ~2%. Although oxygen combined with the constituent metals to form oxides, dispersed nanosized oxides could improve the mechanical properties of HEAs prepared by powder metallurgy. The feasibility of powder metallurgy for HEAs was proven by this work.
查看更多>>摘要：The effects of the extrusion temperature and extrusion ratio on the microstructure, corrosion resistance, and mechanical properties of Mg–Zn–Gd–Y–Zr alloy were investigated. The dynamically recrystallized grain sizes were found to increase with increasing temperature at a given extrusion ratio. At a smaller extrusion ratio, the alloys consist mainly of a bimodal grain structure. Although these have better ultimate tensile strength (UTS) and yield strength (YS), their elongation (EL) and corrosion resistance are not as good as those of the alloys with a larger extrusion ratio extruded at the same temperature. When the extrusion temperature reaches the higher range of 340–380 °C with an extrusion ratio of 12, the alloy has little bimodal structuring. The alloy extruded at 340 °C with an extrusion ratio of 12 had a uniform microstructure and exhibited relatively good corrosion resistance in addition to having good mechanical properties. The ways in which the mechanical properties of this alloy varied with the duration of corrosion through immersion in simulated body fluid were also studied. The rate of decline in the EL was significantly greater than that in the YS, and these were found to have half-life values of 20 days and 51 days, respectively.
查看更多>>摘要：Effects of B or C on the solidification microstructures of Co-Ni-Al-W-based superalloys are studied. The addition of B from 0 to 0.50 at% significantly decreases the solidus temperature from 1270 to 1249 °C and enlarges the solidification temperature range from 87 to 96 °C. The addition of B increases the solidification segregation of Mo, Ta, Ti, Nb, Cr and W, and promotes the formation of Laves phase and (γ + γ′)e eutectic, but suppresses the formation of β phase. M3B2 forms at the final solidification stage when the content of B reaches 0.10 at%. The addition of C reduces the segregation of Ta, Ti, Nb, W; suppresses the formation of the Laves phase, (γ + γ′)e eutectic and β phase. Dot-shaped and rod-shaped MC carbides form when the content of C reaches 0.10 at%, and MC carbides can refine the primary dendrites arm spacing. The above results provide experimental basis for the composition design and heat treatment optimization of the Co-Ni-Al-W-based superalloys.
查看更多>>摘要：The multi-arc ion plating technology is used to prepare CrN coating on the valve seat material surface. Results show that the surface grains gradually increase in size and becomes less uniform with the increase of the Cr target current. At different Cr target currents, the main phases of the CrN coating are Cr, CrN, and Cr2N. The critical load of the coating and matrix is 49.2 N. When the Cr target current is 65 A, the nano-hardness is maximum (18.84 GPa), and Young ’s modulus is 255.41 GPa. The CrN coating can reduce the friction coefficient of the valve seat material from 0.62 to 0.48, thereby improving the wear-resistance behavior. The main wear mechanism is abrasive wear.
查看更多>>摘要：Constructing functionalized carbons decorated with transition metal oxide is an efficient way to combine the cycling stability and high specific capacitance of electrodes for electric double layer capacitors and pseudocapacitors, and the morphology is undoubtedly a key factor for the electrochemical performance. Here, three activated carbons derived from biomass with different morphologies are obtained by carbonizing rosewood (R), corncob (C) and lotus seedpod (L) waste plant body, and then the bio-activated carbons decorated with Co3O4 are prepared by simple oxidation-precipitation and crystallization method. Among the R, C, L carbons, Co3O4, R-Co3O4, C-Co3O4 and L-Co3O4 composites, the L-Co3O4 composite shows best electrochemical performance. At a scan rate of 5 mV s?1, its specific capacitance reaches 1405.3 F g?1 (975 C g?1 at 1 A g?1). Furthermore, a hybrid capacitor is fabricated using L-Co3O4 as the positive electrode and activated carbon as the negative electrode, resulting in energy density of 23.1 W h kg?1, tremendous power density of 3990.6 W kg?1 and high cycling stability (80.2% retention and coulombic efficiency of 98.8% after 5000 cycles). The equipped hybrid supercapacitor device can work for more than 10 min by lighting a red bulb. Thus, this unique L-Co3O4 composite with simple fabrication method can be considered to be a promising candidate for the electrochemical energy conversion and storage.
查看更多>>摘要：Thermoelectric power generation using distributed waste heat energy has received attention as a long-life, environmentally friendly power supply. The intermetallic compound Mg2Si is a lightweight, mid-temperature thermoelectric material that contains no toxic elements, and its thermoelectric performance has been enhanced by various methods such as impurity doping, nanostructuring, and alloying. In this study, we examined the influence of the influence of co-doping with Sb and dilute amounts of the isoelectronic impurity C on the thermoelectric properties of Mg2Si. We fabricated dense polycrystalline specimens of Mg2CxSbySi using the melting process and subsequent plasma-activated sintering. Doping Mg2Si with Sb increased the electrical conductivity ~102 times. Further co-doping with isoelectronic C did not significantly change the electrical conductivity; however, it did reduce the thermal conductivity independently of the electrical properties. Consequently, the specimens co-doped with Sb and C achieved higher thermoelectric performance than specimens of Mg2Si single-doped with Sb. The dimensionless figure of merit ZT of the co-doped specimens reached 0.79 at 873 K over the temperature range 323–873 K.
查看更多>>摘要：Photoconductive and heterojunction devices prepared based on n-type β-Ga2O3 have been extensively studied in the field of solar-blind ultraviolet (UV) detectors. However, for exploiting the full potential of photodetection by preparing bipolar homojunction devices, constructing p-type β-Ga2O3 through rational design remains a challenge. Herein, a p-type β-Ga2(SexO1?x)3 thin film was successfully prepared by a dilute-selenium alloying process. The bandgap was effectively regulated by varying the Se-content in the films. Meanwhile, the energy offset of valence band maximum and Fermi level is estimated to drop from 3.19 eV to 1.72 eV, indicating a transition of the semiconductor type from n-type to p-type. The β-Ga2(Se0.05O0.95)3 film prepared at the incident power of 120 W exhibited p-type conductivity, which possesses hall hole mobility of 24.3 cm2/V·s, hole concentration of 8.23 × 1014 cm?3, and resistivity of about 310.7 Ωcm at room temperature. This work clarified a possible way to realize p-type β-Ga2O3 by semiconductor alloying.
查看更多>>摘要：All-inorganic CsPbI2Br material has attracted considerable attention due to its good balance between phase stability and absorption capacity. However, the power conversion efficiency (PCE) and device stability of CsPbI2Br-based perovskite solar cells (PSCs) still lag far behind those of their counterparts, mainly deriving from the notoriously poor moisture stability under humid environment and large serious charge recombination. Herein, a typical phenethylammonium chlorine (PEACl) and its fluorinated derivative 4-fluoro-phenethylammonium chlorine (F-PEACl) are individually incorporated to modify the surface of CsPbI2Br film to ameliorate the above issues. Benefiting from the comprehensive passivation effect of ammonium halogen, the trap states of treated CsPbI2Br are vastly suppressed. In particular, fluorination significantly increased the dipole moment and hydrophobic property of F-PEACl. Thus, the present CsPbI2Br PSC achieves a champion PCE of 16.29% with high open-circuit voltage of 1.272 V, while the reference device and PEACl-treated device yield PCEs of 14.30% and 15.64%, respectively. More importantly, the PSC with F-PEACl capping layer retains 87.2% of its initial PCE after 1000 h storage under 20% RH ambient without encapsulation. Our results reveal the underlying mechanism of performance improvement by surface passivation strategy and provide an effective approach to further boost the CsPbI2Br PSC efficiency and stability.
查看更多>>摘要：In face-centered cubic alloys, an outstanding combination of strength and ductility can be achieved through reducing the stacking fault energy. In this paper, the mechanical response and microstructural evolution of Ni-27 W alloys (with 27 wt% W) are studied. The Ni-27 W solid solution alloys have a face-centered cubic structure. A stacking fault energy of ~67 mJ/m2 is evaluated by the thermodynamic method. The yield stress, ultimate tensile strength, and percentage elongation to fracture of the Ni-27 W alloys are 415 MPa, 1285 MPa and 42%, respectively, which shows a high strain hardening capacity. The deformation mechanism of the Ni-27 W alloys has been investigated by means of transmission electron microscopy, electron backscatter diffraction, and high-energy x-ray diffraction at the deformation stages with true strains of 0.02, 0.1, 0.2, and 0.3. A fiber texture with <111> and <001> parallel to the tensile direction is gradually formed under uniaxial deformation. Planar dislocation structure is clearly observed, the spacing of which gets thinner as increasing the deformation strain. Planar slip dominates the plastic deformation, which results in a high strain hardening capacity.
查看更多>>摘要：Co-doping with Sm3+ ions into the Eu3+-doped phosphors can bring interesting properties due to the energy transfer of Sm3+→Eu3+. Herein, Sm3+/Eu3+ co-doped phosphors Li3Ba2La3(WO4)8:xSm3+/yEu3+ were synthesized to witness this fact. Upon excitation of 404 nm light, Sm3+/Eu3+ co-doped phosphors show the characteristic emissions of both Sm3+ and Eu3+. The intensity of Sm3+ emission decreases along with the improving Eu3+ concentration, whereas the intensity of Eu3+ emission gets promoted. For Li3Ba2La2.87Sm0.08Eu0.05(WO4)8, the quantum yield reaches up to 53%. Moreover, co-doping Sm3+/Eu3+ phosphor Li3Ba2La2.87Sm0.08Eu0.05(WO4)8 possess better fluorescence thermostability than sole Eu3+ doping phosphor Li3Ba2La2.87Sm0.08Eu0.05(WO4)8, by a factor of about two. The total PL integral intensity at 450 K of Li3Ba2La2.87Sm0.08Eu0.05(WO4)8 remains 83% of that at 300 K, ensuring its applications in high power White Light Emitting Diodes (WLED).
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Elsevier