Microstructural Characterization and Mechanical Behaviors of High Entropy Alloys at Room and Elevated-Temperatures

High entropy alloys (HEAs) are proposed as solid-solution alloys containing five or more principal elements in equimolar or near-equimolar ratios, possessing a single crystal structure rather than several ordered phases. Several studies of HEAs have been performed, with focus on the mechanical behavior and characterization of microstructures. The mechanical behavior and properties of HEAs under various conditions, i.e., strain rates, grain sizes, and temperatures, exhibit great differences, such as strong work hardening, homogeneous macroscopic flow, and excellent compression or tension ductility with obvious serrations at room temperature, and partial or complete dynamic recrystallization at high temperatures. The strong and ductile single-phase body-centered-cubic (BCC) HfNbTaTiZr refractory high-entropy alloy (RHEA) is a potential structural material for high-temperature applications. The present work will focus the mechanical properties and serration behavior in HfNbTaTiZr HEAs, by applying transmission electron microscopy (TEM), atom probe tomography (APT), synchrotron diffraction, and scanning electron microscopy (SEM) to the study of plastic deformation and fatigue behaviors in HEAs under different conditions (covering a wide range of strain rates, temperatures, and tension behaviors), in order to reveal the underlying mechanisms of the plastic deformation for HEAs and to predict the fracture stress. Specifically, an anomaly in strain hardening was observed at elevated temperatures–the strain-hardening exponent decreases expectedly from 77 K to 298 K but reverts to an anomalous ascending trend afterwards. Flow serrations at 673 and 773 K implied the dynamic strain aging (DSA) as an extra strengthening mechanism contributing to the intensified strain hardening at elevated temperatures. The superior fatigue properties during cyclic loading were investigated at room temperature, which present a series of substructures, including dislocation loops, jogs, and dislocation network. The resulting dislocation network was formed by the interaction between dislocations with different Burgers vectors, which can act as the obstacle to dislocation motion to strengthen the fatigue behavior and release the strain energy and stress concentration to improve the resistance to cyclic loading. Moreover, the recrystallization, grain growth and phase transformation of HfNbTaTiZr HEAs were investigated as well in the certain range of temperatures to better understand their grain growth kinetics and phase stability in body centered-cubic (bcc) HEAs, which will be helpful for the materials design and optimization

Analysis of social media’s online expression strategy for social hot spots based on the perspective of mass communication - Take “Bilibili” as an example

With the rapid development of information technology on the Internet and the establishment of new online media platforms, it has played a great role in the delivery of information and the reception of content. The new media have profoundly influenced people’s lives in terms of the way they communicate, the construction of ideas and the execution of processes. This has not only enriched the ways in which news is disseminated, but has also opened up wider avenues and channels for news reporting. Since 2009, Bilibili has grown into a representative domestic secondary platform which is a high-density group of young internet users. The development and dissemination of social events that cater to the moods and emotions of young people can also serve to moderate cultural tensions to some extent, but, if used poorly, can be counterproductive. It is important to pay attention to the issue of culture, both to prevent pan-entertainment and to achieve cultural identity. In the face of online public opinion, government news media should change their previous negative attitude and adopt new and timely methods of response. The correct way to guide public opinion in hot events is a problem that the news media has to face and urgently needs to solve

A Density Peak-Based Clustering Approach for Fault Diagnosis of Photovoltaic Arrays

Fault diagnosis of photovoltaic (PV) arrays plays a significant role in safe and reliable operation of PV systems. In this paper, the distribution of the PV systems’ daily operating data under different operating conditions is analyzed. The results show that the data distribution features significant nonspherical clustering, the cluster center has a relatively large distance from any points with a higher local density, and the cluster number cannot be predetermined. Based on these features, a density peak-based clustering approach is then proposed to automatically cluster the PV data. And then, a set of labeled data with various conditions are employed to compute the minimum distance vector between each cluster and the reference data. According to the distance vector, the clusters can be identified and categorized into various conditions and/or faults. Simulation results demonstrate the feasibility of the proposed method in the diagnosis of certain faults occurring in a PV array. Moreover, a 1.8 kW grid-connected PV system with 6×3 PV array is established and experimentally tested to investigate the performance of the developed method

Atom-light superposition oscillation and Ramsey-like atom-light interferometer

Coherent wave splitting is crucial in interferometers. Normally, the waves after this splitting are of the same type. But recent progress in interactions between atom and light has led to the coherent conversion of photon to atomic excitation. This makes it possible to split an incoming light wave into a coherent superposition state of atom and light and paves the way for an interferometer made of different types of waves. Here we report on a Rabi-like coherent-superposition oscillation observed between an atom and light in a Raman process. We construct a new kind of hybrid interferometer based on the atom–light coherent superposition state. Interference fringes are observed in both the optical output intensity and atomic output in terms of the atomic spin wave strength when we scan either or both of the optical and atomic phases. Such a hybrid interferometer can be used to interrogate atomic states by optical detection and will find its applications in precision measurement and quantum control of atoms and light

Atom-Light Hybrid Interferometer

A new type of hybrid atom-light interferometer is demonstrated with atomic Raman amplification processes replacing the beam splitting elements in a traditional interferometer. This nonconventional interferometer involves correlated optical and atomic waves in the two arms. The correlation between atoms and light developed with the Raman process makes this interferometer different from conventional interferometers with linear beam splitters. It is observed that the high-contrast interference fringes are sensitive to the optical phase via a path change as well as the atomic phase via a magnetic field change. This new atom-light correlated hybrid interferometer is a sensitive probe of the atomic internal state and should find wide applications in precision measurement and quantum control with atoms and photons

A new coordination tetra­mer of copper(I) iodide and benzyl­dimethyl­amine: tetra-μ3-iodido-tetra­kis[(benzyl­dimethyl­amine-κN)copper(I)]

The title compound, [Cu4I4(C9H13N)4], has a distorted cubane-like [Cu4I4] core structure. Each CuI atom is tetra­hedrally coordinated by three I atoms and one N atom of an benzyl­dimethyl­amine ligand. Each I atom acts as a μ3-ligand, linking three CuI atoms. The Cu—I bond distances vary between 2.6328 (7) and 2.7121 (6) Å, while the Cu—N bond distances vary between 2.107 (3) and 2.122 (3) Å

Di-μ-hydroxido-bis­({2,2′-[propane-1,3-diylbis(nitrilo­methyl­idyne)]diphenolato}iron(III)) dimethyl­formamide disolvate

The structure of the title compound, [Fe2(C17H16N2O2)2(OH)2]·2C3H7N, consists of centrosymmetric dimeric units in which crystallographically equivalent FeIII ions are doubly bridged by hydroxide groups. Each FeIII center in the complex has a six-coordinated distorted cis-FeN2O4 octa­hedral geometry