查看更多>>摘要：? 2022 Elsevier B.V.The critical temperature (Thci) corresponding to the load relaxation measured during the solidification of alloy in a ‘T′-shaped mold is introduced into the Clyne-Davies’ model, so that it can be used to predict the hot tearing susceptibility (HTS) of alloy under non-equilibrium cooling. Then, the improved model is applied to study the HTS of Mg–Znx–Y2–Zr0.06 (x = 0.5, 1 and 1.5 at%) alloys under two initial mold temperatures, i.e., two cooling rates. It is found that HTS is very sensitive to both Zn content and initial mold temperature, and the increase in Zn content or initial mold temperature can reduce HTS of the alloy. However, their micro mechanisms are different. The reason for the decrease in HTS with the increase in Zn content is the decrease in the dendrite coherency temperature. Specifically, the ratio of unconstrained feeding stage to intergranular feeding stage increases, and the intergranular liquid phase with eutectic composition increases in the later stage of solidification. The HTS decreases with the increase in the initial mold temperature because the solidification shrinkage stress is relieved. Consequently, the residual liquid phase between the grains can be fed in a more timely manner.
查看更多>>摘要：? 2022 Elsevier B.V.In this paper, 500–600 nm hierarchical flower-like Cu2CdSnS4 (CCTS) was synthesized by two-step method, which was applied in the photodegradation to malachite green (MG) for the first time. With spherical CdSn(OH)6 prepared by co-precipitation method as the precursor, flower-like CCTS micro/nano structured crystals were synthesized by microwave method. The formation of CCTS experienced CdSn(OH)6 coordinating with sulfur source, then dissolving partly to combine with Cu2+ in the existence of PVP as the capping agent, finally to form flower-like structure. The characterization of products showed that stannite CCTS had narrow bandgap and large special interface area, contributing to excellent photodegradation to MG up to 90.29%. The decomposition of MG may originate from N-demethylation, removal of the benzene ring and ring-open reactions. The deep understanding of the photodegradation mechanism may provide the guidance in the long-term study of MG.
查看更多>>摘要：? 2022 Elsevier B.V.In-situ TEM investigations are carried out on the Zr-20Nb alloy to study the evolution of ω phase under the influence of 2 MeV electrons at different temperatures. The Selected Area Diffraction (SAD) patterns taken during the irradiation show characteristic features of ω phase formation like diffuse scattering and streaking of the diffraction spots. Continuous shifting of the peak intensity maxima is observed during the course of transformation. This behaviour is rationalised in terms of the existence of sub-units of ω phase like ω3, ω5, ω7 predicted through Monte-Carlo simulations. Simulated SAD patterns also show the effect of ordering and the aspect ratios of these sub-units on the streaking behaviour. Density functional theory based simulations predict an increasing ω phase formation tendency with decreasing Nb concentration in the alloy. The deviation in the peak shift as a function of irradiation time establishes that with increasing irradiation temperature and electron energy, the ω phase destabilises after certain duration of irradiation which is attributed to the increased vacancy concentration in the alloy induced by 2 MeV electrons.
查看更多>>摘要：? 2022 Elsevier B.V.This work investigated the evolution mechanism of grain boundaries in TC11 alloy after electroshock treatment (EST) using electron back scatter diffraction (EBSD) and transmission electron microscopy (TEM). TEM results showed that abundant α martensite (αM) phase was precipitated after EST with 0.06 s. EBSD results indicated that the percentage of high angle misorientation grain boundaries (HAGBs) in β phase increased from 3.74% before EST to 11.15% after 0.04 s EST, without evident change in proportion of α phase, which resulted from the low angle misorientation grain boundaries (LAGBs) of secondary α (αs) and β phase migrated to the α/β phase boundaries to form HAGBs during the αs to β phase transformation. The proportion of HAGBs in α phase increased from 23.16% before EST to 76.61% after 0.06 s EST, caused by the accumulation of LAGBs at the α/β phase boundaries to form HAGBs. The values for misorientation angle preference selection of α phase located around 60° and 90° were changed to 30° in HAGBs of β phase, and the texture distribution of α phase was uniform with maximum intensity of 5.47 after EST by 0.06 s
查看更多>>摘要：? 2022 The AuthorsGiven the need to process anodes and composites based on nano-YSZ in reducing or in air containing additional CO2 atmospheres for the fabrication of solid oxide fuel cells (SOFCs), and solid oxide electrolysis cells (SOECs), we have studied the effect of the exposure to CO+N2/H2 or CO2+air mixtures during sintering of YSZ green pellets, prepared from commercial nanopowders, on their structure, microstructure, chemical composition and their electrical properties. The reduced sample shows Raman bands at 1298 and 1605 cm?1 that are assigned to the D and G bands of carbon, respectively. The bands intensity ratio ID/IG indicates a larger content of disordered carbon. X-ray photoelectron spectroscopy (XPS) shows that C is present in the reduced samples as reduced carbon. However, the samples sintered in CO2+air present C as carbonate-type. Impedance spectroscopy reveals that the highest total conductivity is for the reduced samples in the whole range of studied temperatures. In addition, sintering in CO2+air causes a detrimental effect on the grain boundary conductivity and therefore, on the total electrical conductivity of YSZ. It can be due to the presence of impurities such as carbonates and oxidised or even, polymerised carbonaceous species located at those areas.
查看更多>>摘要：? 2022 Elsevier B.V.The influence of minor Ag addition on microstructure and properties of powder metallurgy Cu-10Fe alloy was investigated systematically. Minor Ag addition can give rise to finer and more homogenous distribution of Fe phase in Cu-10Fe-0.5Ag alloy. The resultant microstructure of Cu-10Fe-0.5Ag alloy can be ascribed to the increased vacancy density in Cu lattice and reduced interface energy of Cu/ Fe by Ag addition, which therefore increased the nucleation rate for Fe phase. Such microstructure of Cu-Fe-Ag alloy is also beneficial to increase both electrical conductivity and mechanical performance. The calculated activation energy from electrical conductivity is decreased from 56.23 kJ/mol of Cu-10Fe alloy to 28.30 kJ/mol of Cu-10Fe-0.5Ag alloy, suggesting the activated precipitation of Fe phase by Ag addition.
查看更多>>摘要：? 2022 The Author(s)The intermetallic phase Al3Ti is a promising candidate to increase the stiffness of aluminum casting alloys due to its high Young's modulus. Reinforcement particles are formed by the in-situ reaction between solid titanium particles and the liquid aluminum melt. A high-shear mixer is used to peel off the reaction layer on the surface of the Ti particles and distribute the Al3Ti particles homogeneously in the melt. This work investigates the dissolution velocity of different size fractions of Ti powder in three different aluminum casting alloys. The results were used to fabricate specimens with different volume fractions of Al3Ti particles by high pressure die casting. Microstructure characterization was performed to investigate the distribution of the Al3Ti particles within the castings. The mechanical properties were determined by tensile tests and resonant frequency analysis.
查看更多>>摘要：? 2022 Elsevier B.V.A trace amount of boron was added into Fe-based coatings prepared on 42CrMo by laser cladding. The effect of additive boron level on the reinforcements and compressive properties of the coating were analyzed; the microstructure evolution and strengthening mechanism of the coating were illustrated by first-principle calculation. When the additive boron level changed in the coating, the reinforcements transformed from NbC type carbide to Cr23C6 type carbide and finally to Fe3C type carbide, and the strength of the coatings improved significantly. When the boron content was raised to 0.75%, the coating exhibited the best compressive strength and plasticity (3510 MPa with 6.39% strain). The compression properties of the coating defined a new space in the strength-ductility map. The addition of boron was beneficial to forming a eutectic structure composed of Fe3C type carbides and γ-Fe by reducing the formation energy of Fe3C. The Fe3C type carbide played an important role in increasing the strength, and the γ-Fe around Fe3C type carbide could improve the plasticity of the coating.
查看更多>>摘要：? 2022 Elsevier B.V.Considering of cost-effective and simple assembly principle of organic-inorganic halide perovskite (OIHP), producing perovskites into polycrystalline thin films from precursor solution has proved to be appealing. In this paper, (C8H9NH3)2PbBr4 was fabricated based on C8H9NH3Br (PEABr) and PbBr2 according to compositions in the vicinity of (PEA)2PbI4, and the two-dimensionally (2D) perovskite was obtained which entitled with superior photoelectric performance, excellent solution processability and flexible substrates compatibility. And hydrophobic nature of spacer cation of aromatic alkylammonium or a large aliphatic both with the highly consistent orientation of 2D perovskites are beneficial for reducing the grain boundaries density. Meanwhile, optimized (PEA)2PbBr4 were obtained via CsBr additive. Systematic material characterizations manifested enhanced surface morphology, photoluminescence efficiency and carrier lifetime of the CsBr modified (PEA)2PbBr4. Then related (PEA)2PbBr4 based photodetectors exhibited a good responsivity of 0.67 AW?1 when detectivity approached 5.2×1011 Jones, and a large on/off ratio about 500 was obtained. Meanwhile, the devices possessed noticeable stability during the optical switch tests with the rise time and decay time about 0.28 s and 0.21 s for CsBr dopped devices illuminated by 385 nm under 10 V bias. More importantly, spectral wavelength selectivity of CsBr based photodetector indicated the potential utilization in ultraviolet detecting when a wide bandgap of 3.018 eV was obtained.
查看更多>>摘要：? 2022 Elsevier B.V.Mid-infrared (MIR) lasers based on nonlinear frequency conversion by nonlinear optical (NLO) crystals are urgently desired for various military and civilian applications. LiInSe2 (LISe) crystal has aroused intense attention due to its remarkable optical properties. However, the presence of point defects in LISe increases absorption loss and degrades the laser damage threshold (LDT), which limits the practical application in high-power MIR lasers. Therefore, it is essential to reveal the defect types and their formation mechanism in LISe, which is beneficial to design a rational strategy to improve the crystal quality. Here, large-sized LISe crystals with a diameter of 26 mm were successfully grown by the optimized Bridgman method using oriented seed crystal. Furthermore, three types of defects, VSe, VLi, and InLi in the as-grown LISe crystals were verified by photoluminescence (PL) spectra. Therefore, we designed the thermal annealing process under Li2Se vapor to compensate for the losses of Li and Se elements and reduce the defect concentration in LISe. Moreover, the evolution of defects in LISe crystals was determined by X-ray photoelectron spectroscopy (XPS), PL and ultrafast transient absorption spectra (TAS). All the experimental results confirm that the defect concentration in LISe greatly decreases and the crystal quality was obviously improved after annealing under Li2Se vapor. More importantly, this work provides a general strategy to reveal the defects in crystals and to improve the crystal quality of MIR chalcogenides for practical applications.
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