查看更多>>摘要：? 2022 Elsevier B.V.In this paper, W-33.3 at% Zr super-saturated solid solution powder was prepared by mechanical alloying, and its formation mechanism and thermal stability were systematically studied. After 30 h of milling, 33.3 at% of Zr was completely dissolved in W, and a super-saturated solid solution with BCC structure was formed. When the milling duration was increased to 50 h, the single BCC phase was transformed into a dual-phase mixture with a super-saturated solid solution and an amorphous phase. Thermodynamic calculations based on Miedema theoretical model suggested that the W-33.3 at% Zr binary system tended to form solid solution first and then transform into amorphous. Furthermore, high resolution transmission electron microscopy observation revealed that grain refinement, lattice distortion and dislocation may play an important role in the process of solid solution expansion and amorphization. Finally, thermal stability tests suggested that the prepared super-saturated solid solution powder has shown good stability at 800 ℃ for 2 h, which provides more possibilities for the application of W-Zr metastable alloy powders.
查看更多>>摘要：? 2022 Elsevier B.V.Laser powder bed fusion (LPBF) is a powerful technique for in-situ alloy development for advanced mechanical properties. This study used LPBF to dissolve TiC in a Ti-6Al-4V matrix and investigated how post-processing heat treatment and carbon content lead to improved strength and ductility. Pre-alloyed Ti-6Al-4V powder was mechanically mixed with up to 1 wt% TiC before undergoing LPBF. A comprehensive set of heat treatments was examined using 0.75 wt% TiC as a model composition. 1 h at 500 °C was deemed suitable for high strength applications, and 3 h at 700 °C was deemed suitable for a good mix of strength and ductility. TiC concentration was then varied from 0 to 1 wt% across both heat treatments. In the high-strength heat treatment, strength was improved to up to 1490 MPa with a ductility of 3.0% using 1 wt% TiC. Remarkably, with a heat treatment of 3 h at 700 °C, both strength and ductility increased to 1170 MPa with 11.5% ductility using 0.5 wt% TiC. These improvements are shown to be caused by solid solution strengthening and the pinning of prismatic dislocation slip.
查看更多>>摘要：? 2022 Elsevier B.V.The metal-hydrogen interaction and its equilibrium conditions allow for distinct properties in metal hydrides (MHs). Based on these properties, MHs have been found to enable a range of novel technologies from thermal compression to sensors, and catalysis. Ni-MH batteries are currently the main application of hydrides in the market. However, new battery concepts such as Li-MgH2, Mn-MH, and hydride-based solid electrolytes have emerged. Fuel cells based on hydrides have also been proposed to convert the chemical “hydride energy” into electrical energy. Based on their unique thermodynamic properties, MHs are also the basis of new concepts in hydrogen compression, heat pumps, cooling systems, and thermal energy storage. Other important applications, including catalysis and chemical speciation have also been considered owing the chemical properties of hydrides. Sensors and smart mirrors based on the dynamic optical, structural, and electrical properties of MHs have been developed. This review summarizes current state-of-the-art along the multiple applications of MHs and provides recommendations on the future progress required to enable a more widespread adoption of MHs beyond their use as hydrogen storage materials.
查看更多>>摘要：? 2022 Elsevier B.V.The creation of considerably effective electrocatalysts to reduce overpotentials is essential for speeding up the sluggish oxygen evolution reaction (OER) processes, which is imperatively required for the practical exploitation of electrochemical water-splitting. Herein, we prepared a unique composite structure, uniformly spherical Ni-MOF decorated with NiMoO4 nanorods on Ni foam (NF), and assessed its performance toward oxygen evolution reaction. The synergistic effect between NiMoO4 and Ni-MOF remarkably promoted the OER intrinsic activity. Moreover, introducing NiMoO4 endowed the composite structure with enhanced electrical conductivity and exposed more active sites. The NiMoO4/Ni-MOF/NF electrode exhibited exceptional electrocatalytic activity in 1.0 M KOH aqueous solution, with a low overpotential of 218 mV to drive the current density of 10 mA cm?2 and a low Tafel slope (67.75 mV dec?1), surpassing the benchmark RuO2. The presented strategy opens a promising candidate for preparing novel non-precious metal OER electrocatalysts derived from MOF materials for sustainable energy applications.
查看更多>>摘要：? 2022 Elsevier B.V.The response of heat-treatment of an Al-5Mg2Si-2Mg alloy fabricated by laser assisted powder bed fusion (LPBF) was investigated for microstructural evolution and mechanical properties. The results showed that the as-LPBFed Al-5Mg2Si-2Mg alloy was featured by the refined compact Al-cells and the divorced Mg2Si eutectic network. After solution at 490 oC for 1 h, the Mg2Si eutectics were broken to form coarse Mg2Si particles. On the contrary, the characteristics of as-aged microstructure included the heritage of Al-cells and divorced Mg2Si eutectics, and the newly formed ultrafine in-situ Mg2Si particles in the matrix. Tensile results indicated that solution with and without subsequent ageing are not effective for strength improvement. The relative density, yield strength and ultimate tensile strength (UTS) of as-LPBFed alloy decreased obviously from 99.25 %, 295 MPa, and 453 MPa to 98.75 %, 167 MPa, and 292 MPa, respectively. On the other hand, the yield strength of 377 MPa, UTS of 488 MPa and elongation of 9.6 % can be achieved after direct ageing at 180 oC for 3.5 h, showing 28 % increase of yield strength in comparison with as-LPBFed alloy, but still with excellent ductility for engineering applications. It is found that the enhanced mechanical properties are mainly attributed to the newly formed ultrafine in-situ Mg2Si particles. From the results above, the direct ageing was found as a suitable heat treatment method capable of enhancing the strength of as-LPBFed Al-5Mg2Si-2Mg alloy.
查看更多>>摘要：? 2022 Elsevier B.V.The charge separation ability and CO2 adsorption capacity of photocatalysts are considered to be two very important influencing factors in photocatalytic CO2 reduction reactions. In this study, mesoporous g-C3N4 (MCN) with high specific surface area is synthesized by constructing a mesoporous structure to quantify the relationship between the CO2 adsorption capacity and the photocatalytic CO2 reduction activity. Moreover, Ag particles functioned as active sites effectively promote the charge separation efficiency and enhance the photocatalytic activity. More importantly, it is confirmed that the synergistic effect between the mesoporous structure (strong adsorption capacity of CO2) and Ag particles (effective charge separation) can significantly enhance the photocatalytic activity. The CO evolution rate of 3.0%Ag/mesoporous g-C3N4 (Ag/MCN) reaches 1.66 μmol?g?1?h?1, which is 2.81, 2.41 and 4.37 times that of pristine MCN, 1.0% Ag/bulk g-C3N4 (Ag/BCN) and pristine bulk g-C3N4 (BCN), respectively. The study provides useful insight into the development of photocatalysts with high activity for CO2 reduction via controlled structure and surface modification engineering.
查看更多>>摘要：? 2022 Elsevier B.V.InSb has superior electronic transport with low bandgap and high mobility of charge carriers, however, its high lattice thermal conductivity makes it less applicable for thermoelectric applications. Herein we report an effective approach to simultaneously enhance the power factor and reduce total thermal conductivity by isoelectronic doping of Bi for Sb. A series of polycrystalline InSb1-xBix is prepared. The enhanced power factor is attributed to the increase of carrier concentration by charge transfer from the Bi d-orbital states to the In 4d-orbital states based on analyses of both the Bi and In L3-edge XANES spectra of InSb1?xBix. The reduced total thermal conductivity arises from the reduced lattice thermal conductivity due to the point defects. The strain field fluctuations are evidenced by the blue shift in Raman spectra of InSb1-xBix. As a result, zT = 0.56 is attained at 700 K, which is 16% higher than the pristine InSb.
查看更多>>摘要：? 2022 Elsevier B.V.Investigations about how to improve the properties of high entropy alloys (HEAs) play a key role in growing their potential for use in future industrial applications. Accordingly, this study aims to shed light on the effects of alloying elements (Si, Cu and Si-Cu co-added) on the microstructure and oxidation performance of the Fe2CoCrNi0.5 based high entropy alloys. To this end, a series of high entropy alloys containing Fe2CoCrNi0.5, Fe2CoCrNi0.5Si0.25, Fe2CoCrNi0.5Cu0.25 and Fe2CoCrNi0.5Si0.25Cu0.25 were produced by electric current assisted sintering (ECAS) method, which is founded on the principle of simultaneous application of high-density electric current flowing through the powder mixture and uniaxial pressure within a short span of time. The oxidation test was carried out in air at 1123 K for 1200 h under cyclic conditions. The X-ray diffraction results showed that all HEAs have simple FCC solid solution phases. Among all HEAs, the oxidation resistance of the alloy exhibited an increasing trend with the Si addition and the best oxidation behavior at 1123 K for 1200 h was noted with Fe2CoCrNi0.5Si0.25, which experienced the least mass change of 4.72 mg cm?2. Cu addition caused the highest mass change of 15.92 mg cm?2 and the thickest oxide scale of 38.2 μm after oxidation for 1200 h. Si addition is observed to enhance the amount of Cr-rich oxide in the scale. The oxide scale formed on HEA with Cu-added and HEA with Si-Cu co-added contained two oxide layers, including an outer layer of Fe-rich oxide and an inner layer of Cr-rich oxide, which showed continuous structure. However, the alloying elements did not play a favorable role in relieving the formation of internal oxidation. Additionally, it has been reported that Fe2CoCrNi0.5Si0.25 HEA can exhibit high resistance to cyclic oxidation, which can be reasoned as an optimum material for structural and high-temperature applications.
查看更多>>摘要：? 2022 Elsevier B.V.For the first time, Bi2Te3 alloys, which have long been known as promising thermoelectric materials for room temperature applications, have been doped with Na atoms to enhance their thermoelectric performance. Bi2Te3 and Bi2?xNaxTe3 alloys were prepared by mono-temperature melting synthesis. Their structural, crystallographic properties and surface morphology were investigated by XRD and SEM analyses. All the prepared alloys showed perfect crystalline structure of single Bi2?xNaxTe3 phase. The thermoelectric properties of the synthesized alloys were measured in the temperature range of 273–473 K. Electrical conductivity of the concerned alloys were measured by the standard four probe method and studied as a function of temperature, showing metal-like behavior. Na-doping enhanced the electrical conductivity significantly due to enhancing of the carrier concentration. The Seebeck coefficient of all alloys exhibited a positive sign, confirming the p-type conduction. Significantly high Seebeck coefficient values were observed at high temperatures. The maximum value was recorded at 266 μV K? 1 for Bi2Te3 at 473 K. Electronic thermal conductivity of the prepared alloys was estimated from Wiedemann-Franz equation. A remarkable reduction of the electronic thermal conductivity was observed against temperature, in correspondence with the electrical conductivity. The materials thermoelectric power factor was calculated based on electrical conductivity and Seebeck coefficient measurements. Also, the power factor was investigated as a function of temperature. The largest value was found for the most Na-doped samples at 299.6 μW/mK2, observed at 413 K.
查看更多>>摘要：? 2022 Elsevier B.V.The Al addition has presented promising application in tailoring the mechanical properties of VCoNi medium-entropy alloys. However, as far as its real application was concerned, the effect of Al addition on the corrosion behavior of VCoNi alloy should also be taken into account, which, however, has not been reported so far. In this paper, Al0.23VCoNi MEA was designed, and its corrosion behavior was investigated by electrochemical and immersion test in 1 M H2SO4 solution at room temperature. The results in the present work suggested that the Al addition worsens the corrosion resistance of VCoNi alloy. Detailed microstructural and Scanning Kelvin Probe Force Microscopy analysis displayed that the refined grains and Al-enriched BCC phase formed in the Al0.23VCoNi alloy, the high-density grain boundaries and the potential difference between the BCC phase and FCC phases accelerate the dissolution of Al0.23VCoNi alloy in the initial stage of corrosion. Moreover, X-ray photoelectron spectroscopy analysis indicated that the V-depleted and (Al3+, Ni2+)-enriched corroded specimen surface decreased the stability of the passive layer, and hence decreased its resistance to pitting corrosion. Therefore, the degradation of the corrosion resistance of VCoNi MEA after the addition of Al is due to the synergic effects of component segregation, increase in grain boundary and deterioration of the stability of the passive layer.
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