Al元素含量对高熵合金Al_xFeTiCrZnCu力学性能的影响

采用第一性原理密度泛函理论,结合平面波赝势和广义梯度近似(GGA),用虚拟晶体近似(VCA)的方法建立高熵合金的固溶结构模型,计算了高熵合金Al_xFeTiCrZnCu的结构性能、弹性性能和生成热.计算结果表明,Al_xFeTiCrZnCu高熵合金的密度随着Al元素含量的增加而减小,晶格常数在Al元素摩尔含量为1时最小. Al元素含量的增加能提高高熵合金Al_xFeTiCrZnCu的力学稳定性.基态总能量和生成热都随着Al元素含量的增加而增加,但是合金系的稳定性和热力学稳定性有所下降.     

Carbon Encapsulation of High Entropy Alloy Nanoparticles with Extraordinary Coercivity and Saturation at Room Temperature

Owing to their unique properties and technological potential, high entropy alloys (HEAs) have become the subject of great interest in the materials science community. HEAs consist of more than four principle elements in equimolar ratio so their configurational entropy is intrinsically greater than one-principle element based. The increasing surface energy and chemical tendency toward clustering of like atoms at low dimension, however, make production of HEA-nanoparticles (HEA-NPs) extremely difficult. A facile production of HEA-NPs inside carbon nanotubes and nanoparticles is demonstrated in this work. Electron microscopic and elemental analyses confirm encapsulated to be solution phase; some embrace carbides and form multidomains with chemical composition ranging from quaternary to quinary phase. Multidomains and nonmagnetic centers create hardening thus promoting coercivity significantly at room temperature. Alloying induces electron redistribution into high spin states, accounting for observed high saturation. Configurational entropy of encapsulated HEA-NPs lies on a range comparable with bulk.     

Microstructure and Mechanical Properties of Novel High-Strength,Low-Activation Wx(TaVZr)100−x (x = 5, 10, 15, 20, 25) Refractory High Entropy Alloys

In this work, novel high-strength, low-activation W_x(TaVZr)_100−x (x = 5, 10, 15, 20, 25) refractory high entropy alloys (RHEAs) were prepared by vacuum arc melting. Their microstructure, compressive mechanical properties, hardness, and fracture morphology were investigated and analyzed. The results show that the RHEAs possess a disordered BCC phase, ordered Laves phase, and Zr-rich HCP phase. Their dendrite structures were observed, and the distribution of dendrites became gradually more dense with an increase in W content. The RHEAs demonstrate high strength and hardness, with these properties being higher than in most reported tungsten-containing RHEAs. For example, the typical W₂₀(TaVZr)₈₀ RHEA has a yield strength of 1985 MPa and a hardness of 636 HV, respectively. The improvement in terms of strength and hardness are mainly due to solid solution strengthening and the increase in dendritic regions. During compression, with the increase in the applied load, the fracture behavior of RHEAs changed from initial intergranular fractures to a mixed mode combining both intergranular and transgranular fractures.     

Screening-Dependent Study of Superconductivity in 3d-Transition Metals Binary Alloys Superconductors

In the present article, we report the screening-dependent study of the superconducting state parameters （SSPs）, viz. electron-phonon coupling strength A, Coulomb pseudopotential μ^＊, transition temperature TC, isotope effect exponent a, and effective interaction strength No V of 3d-band transition metals binary alloys superconductors have been made extensively in the present work using a model potential formalism and employing the pseudo-alloy-atom （PAA） model for the first time. Five local field correction functions proposed by Hartree （H）, Taylor （T）, Ichimaru-Utsumi （IU）, Farid et al. （F） and Sarkar et al. （S） are used in the present investigation to study the screening influence on the aforesaid properties. The present results of the SSPs obtained from H-screening are found in qualitative agreement with the available experimental data wherever exist.     

求解双曲守恒律方程的高分辨率熵稳定格式

熵稳定格式从物理概念出发,保证总熵关于时间耗散,在计算过程中无需进行熵修正,有效避免如膨胀激波,负压力等非物理现象,显示出独特的优点.通过插入限制器和在单元交界面处进行高阶重构,得到一类高分辨率的熵稳定格式.算例结果表明,格式具有可靠性,高精度和基本无振荡性等特点.     

求解双曲守恒律方程的高分辨率熵相容格式

为提高熵相容格式的精度,利用限制器机制构造高分辨率格式,将构造的通量限制器插入熵相容格式,得到一类高分辨率熵相容格式.构造Euler方程高分辨率熵相容格式时,对熵相容格式中的几个参数做简单调整,提高了接触间断处的分辨率.将所得格式的数值结果与熵相容格式的数值结果比较表明,构造的高分辨率熵相容格式具有稳健和基本无振荡等特性.     

AlCrFeCuNi高熵合金力学性能的分子动力学模拟

高熵合金具有传统合金无法比拟的高强度、高硬度和高耐磨耐腐蚀性,具有广阔的应用前景。为研究AlCrFeCuNi高熵合金(High entropy alloy,HEA)在轴向载荷作用下的力学性能,采用分子动力学方法,模拟高熵合金的实验制备过程并建立原子模型,研究温度和Al的含量对AlCrFeCuNi高熵合金力学性能的影响,从材料学角度分析了变形过程及其具有高塑性的原因。模拟结果表明,AlCrFeCuNi高熵合金在拉伸载荷作用下依次经历弹性、屈服、塑性3个变形阶段。在屈服阶段,开始出现孪晶和层错,孪晶和层错的产生和生长是合金产生不均匀塑性变形的主要原因之一。高熵合金的杨氏模量和屈服应力随着Al含量的增加近似线性降低,同时具有很强的温度效应,温度越低,Al含量越小,其杨氏模量和屈服应力的下降幅度越大。     

高压下Al基合金的凝固组织特征

 研究了亚共晶或过共晶Al-Cu和Al-Si合金在5 GPa压力条件下凝固的显微组织特征。与常压相比,高压不仅会明显改变凝固组织形态,而且会使凝固组织尺寸发生变化,有时粗化,有时细化。凝固组织粗化还是细化与压力对液固两相区温度间隔的影响有关。当压力使液固两相区温度间隔增大时,凝固组织粗化,反之细化。此外,还提出了一种针对树枝晶和胞状晶两种不同形态组织的尺寸评价新方法。     

V-Ta合金力学行为的计算与实验研究

用第一性原理方法计算V-Ta合金体系的弹性常数并对其力学性能进行评估.计算得到的杨氏模量、剪切模量、柯西压力及体模量与剪切模量等表明当合金中Ta的含量在10 wt.%左右时,合金具有较高的强度和良好的塑性.为了检验计算结果,合成了V-10 wt.%Ta,V-15 wt.%Ta,V-20 wt.%Ta等不同Ta含量体系,并对其力学性能进行表征,实验所得结果与计算相吻合,为通过计算设计合金提供了一种可行思路.     

Studying the Effect of Cold Rolling and Heat Treatment on the Microstructure and Mechanical Properties of the Fe36Mn20Ni20Cr16Al5Si3 High Entropy Alloy

In this study, a multi-component FeMnNiCrAlSi high-entropy alloy, chosen through Thermo-Calc^® software (2021a, Stockholm, Sweden) calculation and produced by electric arc melting, was studied for phase continents and mechanical properties. The results elucidated that the cold rolled condition (area reduction ratio about 86%) was in the form of elongated grains with a dendritic structure. Also, small amounts of the BCC phase were precipitated at the grain boundaries. The annealed sample shows features of BCC phase and different sizes of intermetallics. These results coincided with the predictions of Thermo-Calc^® software calculations. A cold rolled sample showed high compressive yield strength of about 950 MPa, and the annealed sample had only half the strength of the cold rolled condition. The cold rolled sample shows the highest micro-hardness. The wear resistance of the annealed condition was significantly improved at room temperature and at 200 °C. The brittle phases in the annealed condition have a positive impact on the wear resistance.     

Pseudo-binary and pseudo-ternary diffusion couple methods for estimation of the diffusion coefficients in multicomponent systems and high entropy alloys

The benefits of using the pseudo-binary and pseudo-ternary diffusion couple methods in multicomponent inhomogeneous systems are demonstrated by estimating different types of composition-dependent diffusion coefficients. These are important for understanding the basic atomic mechanism of diffusion and complex compositional evolutions. These were otherwise considered impossible during the last many decades. Without any options previously, sometimes the average values over a composition range of random choice were estimated, which are not the material constants but depend on the composition range and also the end member compositions. The steps and analyses for utilising the pseudo-binary and pseudo-ternary methods are first described in the Ni-Co-Fe-Mo system by producing the ideal diffusion profiles fulfilling the concepts behind these methods. Following, the discussion is extended to the systems related to medium (Ni-Co-Cr) and high (Ni-Co-Fe-Mn-Al) entropy alloys. In fact, this is the first report showing a correct experimental method that should be followed for the estimation of the interdiffusion and intrinsic diffusion coefficients in inhomogeneous high entropy alloys. In the end, the limitations of following these methods because of the generation of non-ideal diffusion profiles are discussed based on experimental results. The steps are also suggested to avoid such complications. These methods are easy to adopt for research engineers. Most importantly, these give an opportunity to validate the data estimated following newly proposed numerical methods by different groups with experimentally estimated diffusion coefficients, which were not possible earlier.     

基于图像熵的高动态范围场景的自动曝光算法

自动曝光控制是通过控制曝光量使图像亮度最优化的过程,由于图像亮度与曝光值有着直接的关系,因而图像亮度在自动曝光算法中被广泛应用.虽然熵已用于各种图像处理应用,但是很少应用在自动曝光中.基于图像熵提出一种新的自动曝光算法,不同于传统的主要依赖于图像亮度的算法.首先根据图像熵值大小来判断光照条件,通过图像熵大小的比较,把图像的各区域划分为感兴趣区域与不感兴趣区域.然后由图像熵值大小采用分配权重方法对不同区域分配权重,最后进行准确地自动曝光.由于该算法主要基于图像熵值的大小,所以曝光效果不受图像中对象位置影响,使得该算法更灵活.实验结果表明,该算法对高动态范围场景可以准确地检测出各种光照条件,提高相机系统输出图像的动态范围,同时还增加了自动曝光的准确性.     

Effects of Nb Additions and Heat Treatments on the Microstructure,Hardness and Wear Resistance of CuNiCrSiCoTiNbx High-Entropy Alloys

In this research, a set of CuNiCrSiCoTi (H-0Nb), CuNiCrSiCoTiNb_0.5 (H-0.5Nb) and CuNiCrSiCoTiNb₁ (H-1Nb) high-entropy alloys (HEAs) were melted in a vacuum induction furnace. The effects of Nb additions on the microstructure, hardness, and wear behavior of these HEAs (compared with a CuBe commercial alloy) in the as-cast (AC) condition, and after solution (SHT) and aging (AT) heat treatments, were investigated using X-ray diffraction, optical microscopy, and electron microscopy. A ball-on-disc configuration tribometer was used to study wear behavior. XRD and SEM results showed that an increase in Nb additions and modification by heat treatment (HT) favored the formation of BCC and FCC crystal structures (CS), dendritic regions, and the precipitation of phases that promoted microstructure refinement during solidification. Increases in hardness of HEA systems were recorded after heat treatment and Nb additions. Maximum hardness values were recorded for the H-1Nb alloy with measured increases from 107.53 HRB (AC) to 112.98 HRB, and from 1104 HV to 1230 HV (aged for 60 min). However, the increase in hardness caused by Nb additions did not contribute to wear resistance response. This can be attributed to a high distribution of precipitated phases rich in high-hardness NiSiTi and CrSi. Finally, the H-0Nb alloy exhibited the best wear resistance behavior in the aged condition of 30 min, with a material loss of 0.92 mm³.     

Entropy as a High-Level Feature for XAI-Based Early Plant Stress Detection

This article is devoted to searching for high-level explainable features that can remain explainable for a wide class of objects or phenomena and become an integral part of explainable AI (XAI). The present study involved a 25-day experiment on early diagnosis of wheat stress using drought stress as an example. The state of the plants was periodically monitored via thermal infrared (TIR) and hyperspectral image (HSI) cameras. A single-layer perceptron (SLP)-based classifier was used as the main instrument in the XAI study. To provide explainability of the SLP input, the direct HSI was replaced by images of six popular vegetation indices and three HSI channels (R₆₃₀, G₅₅₀, and B₄₈₀; referred to as indices), along with the TIR image. Furthermore, in the explainability analysis, each of the 10 images was replaced by its 6 statistical features: min, max, mean, std, max–min, and the entropy. For the SLP output explainability, seven output neurons corresponding to the key states of the plants were chosen. The inner layer of the SLP was constructed using 15 neurons, including 10 corresponding to the indices and 5 reserved neurons. The classification possibilities of all 60 features and 10 indices of the SLP classifier were studied. Study result: Entropy is the earliest high-level stress feature for all indices; entropy and an entropy-like feature (max–min) paired with one of the other statistical features can provide, for most indices, 100% accuracy (or near 100%), serving as an integral part of XAI.     

Theil Entropy as a Non-Lineal Analysis for Spectral Inequality of Physiological Oscillations

Theil entropy is a statistical measure used in economics to quantify income inequalities. However, it can be applied to any data distribution including biological signals. In this work, we applied different spectral methods on heart rate variability signals and cellular calcium oscillations previously to Theil entropy analysis. The behavior of Theil entropy and its decomposable property was investigated using exponents in the range of [−1, 2], on the spectrum of synthetic and physiological signals. Our results suggest that the best spectral decomposition method to analyze the spectral inequality of physiological oscillations is the Lomb–Scargle method, followed by Theil entropy analysis. Moreover, our results showed that the exponents that provide more information to describe the spectral inequality in the tested signals were zero, one, and two. It was also observed that the intra-band component is the one that contributes the most to total inequality for the studied oscillations. More in detail, we found that in the state of mental stress, the inequality determined by the Theil entropy analysis of heart rate increases with respect to the resting state. Likewise, the same analytical approach shows that cellular calcium oscillations present on developing interneurons display greater inequality distribution when inhibition of a neurotransmitter system is in place. In conclusion, we propose that Theil entropy is useful for analyzing spectral inequality and to explore its origin in physiological signals.     

First-Principles GGA+U Study of Intermediate-Band Characters from Zn_(1-x)M_xO(M=3d Transition-Metal) Alloys Suitable for High Efficiency Solar Cell

The electronic structure characters are calculated for the Zn_(1-x)M_xO alloys with some Zn atoms in ZnO substituted by 3d transition-metal atoms(M),in order to find out which of these alloys could provide an intermediate band material used for fabricating high efficiency soiar cell.Especially,among of these alloys,the electronic structure character and optical performance of Zn_(1-x)Cr_xO alloys clearly show an intermediate band Med partially and isolated from the VB and the CB in energy band structure of ZnO host,and the intermediate band characters can be preserved with increasing Cr concentrations no more than 8.33%in Zn_(1-x)Cr_xO alloys,at the same time,the ratio 0.52 of E_g~(FC) to E_g~(VE) in Zn_(1-x)Cr_xO,(x = 4.16%) alloy is closest to the optimal ratio of 0.57.Besides,compared to the ZnO,the optical absorption does indicate a great improved absorption below the calculated band gap of the ZnO and an enhancement of the optical absorption in the whole solar spectral energy range.     

Entropy and Network Centralities as Intelligent Tools for the Investigation of Terrorist Organizations

In recent years, law enforcement authorities have increasingly used mathematical tools to support criminal investigations, such as those related to terrorism. In this work, two relevant questions are discussed: “How can the different roles of members of a terrorist organization be recognized?” and “are there early signs of impending terrorist acts?” These questions are addressed using the tools of entropy and network theory, more specifically centralities (degree, betweenness, clustering) and their entropies. These tools were applied to data (physical contacts) of four real terrorist networks from different countries. The different roles of the members are clearly recognized from the values of the selected centralities. An early sign of impending terrorist acts is the evolutionary pattern of the values of the entropies of the selected centralities. These results have been confirmed in all four terrorist networks. The conclusion is expected to be useful to law enforcement authorities to identify the roles of the members of terrorist organizations as the members with high centrality and to anticipate when a terrorist attack is imminent, by observing the evolution of the entropies of the centralities.     

Sample Entropy as a Tool to Assess Lumbo-Pelvic Movements in a Clinical Test for Low-Back-Pain Patients

Low back pain (LBP) obviously reduces the quality of life but is also the world’s leading cause of years lived with disability. Alterations in motor response and changes in movement patterns are expected in LBP patients when compared to healthy people. Such changes in dynamics may be assessed by the nonlinear analysis of kinematical time series recorded from one patient’s motion. Since sample entropy (SampEn) has emerged as a relevant index measuring the complexity of a given time series, we propose the development of a clinical test based on SampEn of a time series recorded by a wearable inertial measurement unit for repeated bending and returns (b and r) of the trunk. Twenty-three healthy participants were asked to perform, in random order, 50 repetitions of this movement by touching a stool and another 50 repetitions by touching a box on the floor. The angular amplitude of the b and r movement and the sample entropy of the three components of the angular velocity and acceleration were computed. We showed that the repetitive b and r “touch the stool” test could indeed be the basis of a clinical test for the evaluation of low-back-pain patients, with an optimal duration of 70 s, acceptable in daily clinical practice.