Search

High-entropy alloys (HEAs) have attracted widespread attention from scholars as a new type of material employed in extreme environments. However, as a main kind of HEAs, many face-centered cubic single-phase HEAs are restricted in industrial applications due to their lower yield strength and high cost when containing expensive elements such as Co. In this study, dispersion strengthening by heat treatment was introduced in low-cost Co-free Fe40Mn20Cr20Ni20 HEA to improve its strength, and its high-temperature tensile behavior and constitutive model were studied to explore its potential application at high temperatures. It is found that when subjected to quasi-static room-temperature stretching, the heat-treated sample exhibits a yield strength of 534 MPa and a tensile plasticity of 26.8%. In addition, the tensile behavior of samples after heat treatment was investigated at high temperature (573–873 K) and low strain rate (10−3–10−1 s−1). The results suggest that the yield strength decreases with increasing temperature and decreasing strain rate. Moreover, at 873 K and 10−3 s−1, the electron backscatter diffraction system and x-ray diffraction results of the deformed sample indicate that the softening curve is driven from the recovery of materials. Finally, the flow stress was predicted using the Arrhenius equation and Artificial Neural Network model (ANN), and the two models were assessed using the average absolute relative error and coefficient of correlation (R). The results showed that the ANN had higher accuracy. [ABSTRACT FROM AUTHOR]

In this study, the synergistic behavior of Ni and Al in two low-density steels (Fe-26Mn-10.2Al-0.98C-0.15V (wt. %) and Fe-29Mn-5Al-1C-12Ni (wt. %)) and their influence on microstructures and mechanical properties were investigated. The chemical composition of κ-carbides and B2 precipitated particles as a function of annealing and aging temperature and the matrix within which they formed were elucidated. The microstructures and deformation mechanisms of both steels were studied based on their strengthening contribution. The Fe-26Mn-10.2Al-0.98C-0.15V steel mainly realized precipitation strengthening through κ-carbides and grain boundary strengthening due to full recrystallization. The strengthening caused by Fe-29Mn-5Al-1C-12Ni steel was mainly due to the presence of the B2 phase in the matrix, which was non-coherent with FCC. This led to the Orowan bypass mechanism, which made precipitation strengthening the main strengthening contribution. The synergistic effect led to the shear or bypass mechanism of both steels when plane dislocation slip occurred. In addition, it also had an influence on the work-hardening capability during plastic deformation. This study provides a promising way to further enhance the yield strength of low-density austenitic steels through the synergistic effect of Ni and Al. [ABSTRACT FROM AUTHOR]

In order to find more excellent structural materials resistant to radiation damage, high-entropy alloys (HEAs) have been developed due to their characteristics of limited point defect diffusion such as lattice distortion and slow diffusion. Specially, refractory high-entropy alloys (RHEAs) that can adapt to a high-temperature environment are badly needed. In this study, T i Z r H f N b M o 0.1 RHEAs are selected for irradiation and nanoindentation experiments. We combined the mechanistic model for the depth-dependent hardness of ion-irradiated metals and the introduction of the scale factor f to modify the irradiation-hardening model in order to better describe the nanoindentation indentation process in the irradiated layer. Finally, it can be found that, with the increase in irradiation dose, a more serious lattice distortion caused by a higher defect density limits the expansion of the plastic zone. [ABSTRACT FROM AUTHOR]

At high temperatures, serrated flows are frequently observed on the stress–strain curves of single-phase high-entropy alloys, indicating their unique mechanical behavior. In the current study, the CoCrFeMnNi (Cantor alloy) alloy was selected as a model material to further verify the temperature dependence on the serrated flow behavior through continuous temperature variation during tensile tests, which shows a certain strengthening effect of the serrated flow. The lattice strain and dislocation density were calculated at different conditions using the Williamson–Hall (W-H) analysis method. Based on the strain dependence of mobile dislocation density and forest dislocation density, a flow stress model related to the Portevin–Le Chatelier (PLC) effect was proposed to quantify the variation in the PLC behavior with the temperature and its influence on flow stress. The model is beneficial to accurately account for the flow stress during plastic deformation at high temperatures. [ABSTRACT FROM AUTHOR]

The Portevin–Le Chatelier (PLC) effect induced by dynamic strain aging is commonly observed in various alloys. The stress-drop magnitude of serrations and the critical strain at which serrations occur are two pivotal features characterizing serrated flow. This study investigates the temperature (160–460 °C) and strain rate (6 × 10−4 s−1–2 × 10−2 s−1) dependence of the serrated flow behavior in the CoNiV medium-entropy alloy through uniaxial tensile tests. Under the guidance of the mean-field theory, a scale theory has been applied to derive a scale function and scale indices that can be used to predict the distribution of stress drops. A normal PLC behavior of critical strain is fitted using the dislocation pinning model, demonstrating the presence of specific solute atoms conforming to the dislocation pinning model within medium-entropy alloys. [ABSTRACT FROM AUTHOR]

In this study, the electrochemical behaviour of CrMnFeNi and CrMnFeNiLa0.1 high-entropy alloys (HEAs) in 0.5 M H2SO4 solutions was investigated. Potentiodynamic polarisation curves and electrochemical impedance spectroscopy (EIS) measurements showed that the addition of rare earth element lanthanum has a positive impact in enhancement of corrosion resistance capacity for CrMnFeNi HEAs. The potentiodynamic polarisation curves of the CrMnFeNi and CrMnFeNiLa0.1 alloys exhibit an extensive passive region ((ΔE>1000 mV). Mott–Schottky analysis showed that the donor densities decreased with the addition of La. The possible mechanism regarding the effect of inclusion of La on the dynamic of passivation process was discussed. [ABSTRACT FROM AUTHOR]

High silica SSZ-13 zeolite was synthesized by an efficient and green steam-assisted crystallization (SAC) method under a low alkalinity and low organic templates amount system. The as-prepared samples were characterized by XRD, SEM, N2 adsorption–desorption, TG–DTG and NH3-TPD. The results showed that the SAC method can not only remarkably improve zeolite yield but also enhance the crystallization rate of SSZ-13 zeolite compare to conventional hydrothermal route. Meanwhile, it was also found that the various content of the organic structure directing agent (N,N,N-trimethyladamantammonium hydroxide, TMAdaOH) in the dry gel can adjust flexibly the crystal size, morphology and acidity of samples. The zeolite samples with smaller particles and more strong acidity amount were more likely obtained under the higher TMAdaOH/SiO2 ratio (0.2) condition. In addition, the catalytic evaluation in methanol-to-olefins (MTO) reaction showed that the high silica SSZ-13 catalysts synthesized by SAC method exhibited longer lifetime and comparative selectivity to ethylene and propene than those of the SSZ-13s obtained by conventional hydrothermal route. Thus, the SAC route is believed to be a competitive strategy to synthesize high silica SSZ-13 zeolites with improved MTO catalytic performance. [ABSTRACT FROM AUTHOR]

Hierarchical mordenite with micropores and mesopores was one-pot synthesized through a soft-templating method using a special diquaternary ammonium-type surfactant as a mesoporogen. The obtained samples were characterized by XRD, N physisorption, SEM, TEM, TG-DTG, Al and Si NMR spectroscopy, and NH-TPD techniques. The catalytic performance of the hierarchical mordenite compared to that of conventional mordenite and mesoporous AlMCM-41 material was evaluated in the benzylation of benzene with benzyl alcohol. The results show that the hierarchical mordenite is highly crystalline and possesses large mesopore volume and strong acidity. Moreover, the prepared hierarchical mordenite catalyst is high-efficiency for the conversion of benzyl alcohol into diphenylmethane due to the superior mass transfer ability and largely accessible acid sites. The apparent reaction rate constant for HMOR is 23 times that for CMOR and 8 times that for AlMCM-41. These results suggest that hierarchical zeolites with mesoporosity and strong acidity may be the ideal catalysts in reactions involving large molecules. [ABSTRACT FROM AUTHOR]

Excitation/emission polarization anisotropies (ρexc/emm) of single CdSe nanowires (NWs) were studied for their size, frequency, and dielectric environment dependencies. Single NW optical experiments show strong ρexc dielectric environment dependencies for both thick and thin NWs in agreement with classical dielectric contrast models. Furthermore, no excitation frequency sensitivities were seen for both thick and thin wires, in air and under poly(methyl methacrylate) (PMMA). Moderate radial dependencies were also found for NWs embedded in PMMA. Complementary emission anisotropy measurements yielded significant radial and dielectric environment sensitivities with statistically smaller ρemm values than ρexc. A moderate ρemm frequency dependence was observed for thin NWs in PMMA. [ABSTRACT FROM AUTHOR]