查看更多>>摘要：The relaxation spectrum of glassy solids has long been considered to probe their structural features and deformation mechanisms. Here, by systematically investigating the structural evolution, dynamical re-laxations and mechanical properties of a Zr-based metallic glass subjected to different cryogenic treatment time, we build a bridge to connect the relaxation processes and mechanical properties. It is found that the /3 -relaxation triggered by local excitations has no memory effect of the thermal history or initial free volume content of the system. However, some local denser areas with a high potential energy created by CT might contribute to /3 '-relaxation that activated at a much lower energy, which may play a crucial important role in the fundamental deformation mechanisms of metallic glasses. The relaxation behaviors and the related improved mechanical properties can be rationalized in terms of the atomic-level stress theory. These findings will advance our understanding of the intrinsic correlation between local excitations and me-chanical properties of metallic glasses, thereby may help guide to develop amorphous alloys with high mechanical performance. (c) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：Small size GaN nanorods (GaN NRs) show new features of the photoluminescence (PL) associated with the enhanced surface effects and the strong electron-phonon coupling. A dominant emission is observed at 3.43 eV; a lower energy with respect to the commonly reported (DXA)-X-0 peak for thicker NRs. The phonon replicas of the silent B1l acoustic phonon mode are well represented in the PL spectra at temperatures up to 150 K inferring the enhanced Frohlich electron-phonon coupling. The B1l phonon mode was previously detected for the grown GaN NRs by resonant Raman scattering under resonance excitation. The enhanced electron-phonon coupling through Frohlich interaction is proven by the calculated Huang-Rhys factor. The low-energy dominant peak intensity is around six times the (DXA)-X-0 peak intensity indicating that the majority of excitons occupy the surface shell of GaN NRs. This study provides new insights on small-size GaN NRs that greatly influence their physical properties for applications in optoelectronics, UV and blue lasers, and high-temperature/high-power electronic devices. (C) 2021 Elsevier B.V. All rights reserved.
Ahmad, IqbalAhmed, JawadBatool, SaimaZafar, Muhammad Nadeem...
9页
查看更多>>摘要：The production of an inexpensive, highly active electrocatalyst for a simple oxygen evolution reaction (OER) based on earth-abundant transition metals is still a major challenge. In addition, the ambiguity of the water splitting reaction (hydrogen evolution and OER) is a hurdle in the manufacture of suitable catalysts for the efficient water electrolysis process. Here, the synthesis of iron oxide/iron phosphide (Fe2O3/FeP) heterostructure and its counterparts Fe2O3 and FeP as cheap electrocatalysts for water electrolysis is presented. Characterization techniques such as powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy were used to analyze the structure of these electrocatalysts. Heterostructure Fe2O3/FeP has been shown to be a more active electrocatalyst than its counterparts. It initiates OER at a remarkably low potential of 1.49 V vs. reverse hydrogen electrode (RHE). For this electrocatalyst, a current density of 10 mA/cm(2) is achieved at an overpotential of 264 mV for OER in 1.0 M potassium hydroxide solution and the value of the Tafel slope is 47 mV dec(-1), outperforming its complements (Fe2O3 and FeP) under similar conditions. The results obtained are superior to those of previously reported Fe-based OER electrocatalysts. The Fe2O3/FeP electrocatalyst has proven its long-term stability by driving OER at 1.65 V (vs. RHE) for about 12.5 h. (C) 2021 Elsevier B.V. All rights reserved.
Zheng, Hang -boLi, Yu-lingWang, Yuan-liMa, Feng...
7页
查看更多>>摘要：The development of efficient, inexpensive, and stable hydrogen evolution reaction (HER) electrocatalysts is the key to large-scale water electrolysis technologies for hydrogen production. Constructing heterojunction electrocatalysts has become one of the effective strategies for designing high-performance HER electrocatalysts due to their unique heterogeneous interfaces. Herein, a new strategy of PH3 assisted synthesis of metaphosphate is reported, which is used to construct Co(PO3)2@NPC/MoS2 heterostructures (where NPC is N-doped porous carbon). The results show that the formation of Co(PO3)2@NPC/MoS2 heterogeneous interfaces can optimize the electronic structure of the electrocatalyst and greatly improve its HER performance. As a result, a lower overpotential of 119 mV at 10 mA cm-2 is obtained in alkaline electrolyte. This work provides a new perspective for the design of high-performance electrocatalysts for electrocatalytic water splitting. (c) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：In this work, the effects of pretwins on the flow behavior, microstructure, and texture evolution of a rolled AZ31 magnesium alloy during hot deformation along three different orthogonal directions were studied via compression tests conducted at 25-350 degrees C. The flow behavior along different directions was discussed based on the operation of different deformation mechanisms in twinned and untwinned regions. Detwinning was the dominant deformation mechanism during compression in the normal direction at low temperatures, but ceased as the temperature increased to 250 degrees C. In the latter condition, the effect of pretwins on the texture reorientation led to a decrease in the yield strength. Pretwins stimulate the microstructure condition preceding dynamic recrystallization (DRX) during the compression of samples along the rolling and transverse directions, leading to lower peak strains. The results showed that the pretwins increased the grain size and fraction of DRX at 250 degrees C. The greatest increase in the DRX fraction was obtained for deformation parallel to the normal direction. The effect of pretwins on the grain boundary characteristics of the samples deformed along the normal direction was investigated. The pretwinned samples showed more significant texture rotation for dynamically recrystallized grains compared with parent grains during deformation parallel to the normal direction. (c) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：Following the introduction of high-entropy alloys (HEAs) with five or more principal elements, dual-phase HEAs have recently received significant attention due to their promising mechanical properties. Theoretical simulations suggest that unique mechanical properties of these alloys arise due to the contribution of localized phase transformation and diverse microstructural behavior of two phases under plastic de-formation. In this study, phase transformations and microstructural evolution in a dual-phase AlFeCoNiCu alloy is investigated experimentally during plastic deformation using the high-pressure torsion (HPT) method. The two BCC and FCC phases exhibit diverse behaviors under plastic straining. The FCC phase with low stacking fault energy forms numerous nanotwins and stacking faults and its lattice is expanded by 3 vol %. The BCC phase accumulates dislocations, and its lattice is contracted by 5 vol%. These diverse micro-structural/structural evolutions, which are partly consistent with the predictions of theoretical simulations, lead to a high microhardness of 495 Hv in this dual-phase HEA. (c) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：Refractory high entropy alloys (RHEAs) have broad prospects in the field of high-temperature structural materials because of their outstanding mechanical properties at high temperatures. In this work, a novel TiNbTaZrHf based composite was fabricated by powder metallurgy in-situ method. By introducing carbides, the TiNbTaZrHf based composite exhibits an ultra-high yield strength of 2620 MPa at room temperature. Meanwhile, the composite still maintains a high strength of 508 MPa at 1000 degrees C. The significant strength improvement can be attributed to the load-bearing effect caused by the dispersed carbides with high vo-lume fraction, while the intergranular fracture of carbides is responsible for the plastic instability. When the temperature rises to 1200 degrees C, the yield strength decreases significantly. The weakening of load-bearing effect and the activation of grain boundary sliding are the main reason for the strength reduction, while interfacial debonding between the matrix and carbides becomes the main failure behavior. (c) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：Metal-organic framework (MOF) has attracted increasing research interest for electrochemical applications due to their high porosity and tailorable structure. In this work, binder-free nickel terephthalate-based MOF nanosheet arrays grown on nickel foam (NF@Ni-BDC) are set as an excellent anode for alkali metal ion batteries. Benefiting from the propelled electrochemical reaction kinetics, enhanced charge diffusion efficiency, and fast infiltration of electrolyte endowed by the self-supported nanoarrays electrode architecture, high capacity of 162 mAh g(-1) can be obtained at a high current density of 400 mA g(-1 )for sodium ion battery, and capacity of 116 mAh g(-1) can be retained after 1000 cycles at 100 mA g(-1) for potassium ion battery, which demonstrate remarkable rate capability and cycling performance. It is verified that the organic linker of Ni-BDC plays a vital role in ionic insertion and desertion processes, while the metal central ions mainly serve as the scaffold to maintain the structural integrity. (C) 2021 Published by Elsevier B.V.
查看更多>>摘要：A series of uniaxial compression experiments were carried out on the as-extruded AZ31 Mg alloy with < 10-10 > - < 11-20 > //ED (extrusion direction) double fiber texture at 200-350 degrees C. The microstructure evolution during the work hardening and dynamic softening stages were systematically investigated based on deformation mechanisms and dynamic recrystallization (DRX), respectively. Experimental and simulation results demonstrated that in the work hardening stage, the dominant deformation mechanisms were the basal < a > slip and {10-12} twinning at 250 degrees C, while the basal < a > slip and prismatic < a > slip 350 degrees C. The appearance of profuse {10-12} twins at 250 degrees C not only effectively refined the microstructure but also quickly promoted the formation of strong < 0001 > //CD (compression direction) texture. Moreover, the activation of twin variants was mainly dependent on their own Schmid factor that was higher in < 10-10 > // CD grains, resulting in the earlier disappearance of the < 10-10 > //ED texture component than the < 11-20 > //ED texture component. In contrast, owing to the limited of {10-12} twins, the samples at 350 degrees C exhibited a weak fiber texture with diffusely distributed of basal plane along the CD. In the dynamic softening stage, high temperature increased both the grain size and proportion of DRXed grains, resulting in a more homogeneous microstructure. More importantly, the continuous DRX (CDRX) transformed into discontinuous DRX (DDRX) as the temperature increased from 250 degrees C to 350 degrees C. The similar orientation between the new CDRXed grains and parent grains at 250 degrees C preserved the strong < 0001 > //CD texture, while at 350 degrees C the basal texture was significantly weakened due to the random orientation DDRXed grains and higher activation of pyramidal < c + a > slip. These findings are beneficial for the optimization of the temperature range of the MDF process. (c) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：Post-sinter annealing is essential to improve the microstructures and magnetic properties in NdFeB-based sintered permanent magnetic materials. In this paper, investigated systemically are the effects of post-sinter annealing on the microstructures and magnetic performance of Ga and Cu co-doping Nd2Fe14B based sintered magnets. It is found out that the intrinsic coercive force of the magnets increased from 9.17 kOe to 18.67 kOe after two stage post-sinter annealing (PSA), which shows an extraordinary increment of 103.5%. The remanence, with a decreasing percentage of 1.95%, slightly decreases from 13.87 kGs to 13.60 kGs. The substantial increase of intrinsic coercivity is mainly attributed to the improvement of clean and thin continuous grain boundary layers, the smoothness of hard magnetic matrix phase and the appearance of the RE6(Fe, M)(14) antiferromagnetic phase during annealing. The reduction of the remanence is caused by the deteriorated orientation degree and reduced volume fraction of hard magnetic main phases after post sinter annealing. (C) 2021 Elsevier B.V. All rights reserved.
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