Fe_3O_4@MgO纳米复合材料的制备及其对Pb~(2+)的吸附性能

采用两步化学沉淀法制备了Fe_3O_4@MgO纳米复合材料,研究了纳米复合材料对Pb~(2+)的吸附性能。结果表明,所制备的复合材料具有较高的顺磁性和稳定性,其饱和磁化强度为58.07 emu/g,初始氧化增重温度为125℃,对Pb~(2+)有较好的吸附能力,在50 min内可以达到吸附平衡,最大吸附量为711.5 mg/g,其吸附过程符合准二级动力学模型和Langmuir等温吸附模型。     

稀土元素对镁合金力学行为影响的研究现状

系统论述了不同稀土元素的结构特性,基于镁合金的强化机制,并结合当前稀土镁合金的研究现状,展示了稀土元素的添加对镁合金在强度、塑性及抗蠕变性能等方面带来的变化,尤其是对镁合金塑性的影响.其中,区别于传统的强化机制,对添加稀土元素后出现的LPSO结构相对镁合金性能的影响也进行了重点讨论,进一步对镁合金中的稀土元素合金化后的改性作用及前景进行了探讨和展望.     

CeO2掺杂制备Ba0.9Ca0.1Ti1-xSnxO3压电陶瓷的结构及电性能

采用传统的陶瓷烧结技术,通过添加0.15%(摩尔分数)CeO2,在1120℃烧结2h,成功制备了新型无铅压电陶瓷Ba0.9 Ca0.1 Ti1-x Snx O3,并且检测了陶瓷样品的微结构和电性能.XRD显示所有陶瓷样品均具有纯的钙钛矿结构,在室温下为典型的四方相,SEM显示适量添加锡离子可以提高陶瓷致密性.在室温下,锡离子改性的BaTiO3基压电陶瓷在x=0.02处显示了优异的压电、介电和铁电性能(d33=276 pC/N,kp=46%,εr=3678,tanδ=2.4%,Pr=18.2μC/cm2,EC=1.12 kV/mm).这些优异的检测结果证实适当添加锡离子能改善BaT iO3基压电陶瓷的电性能.     

不同钙硅比水化硅酸钙力学性能的分子动力学模拟

基于Pellenq等的建模思路,构造了不同钙硅比(C/S)的水化硅酸钙(C-S-H)原子模型,采用分子动力学方法模拟了C-S-H在轴向拉伸载荷作用下的力学性能。重点比较分析了不同钙硅比的C-S-H在无水及含水情况下的拉伸应力-应变曲线。模拟结果表明:(1)与钙硅比为1.0的情况相比,钙硅比大于1.0时C-S-H结构的抗拉强度显著下降;(2)钙硅比大于1.0时,钙氧间的相互作用在承受载荷方面起重要作用,有效弥补了结构中因SiO_2基团缺失引起的缺陷,使得C-S-H的强度下降程度趋缓;(3)当应变达到一定程度时,水分子能够切断钙氧间的相互作用,使得C-S-H结构的强度进一步降低甚至引起断裂失效。     

Additive Manufacturing of Titanium Alloys by Electron Beam Melting: A Review

Electron beam melting (EBM), as one of metal additive manufacturing technologies, is considered to be an innovative industrial production technology. Based on the layer‐wise manufacturing technique, as‐produced parts can be fabricated on a powder bed using the 3D computational design method. Because the melting process takes place in a vacuum environment, EBM technology can produce parts with higher densities compared to selective laser melting (SLM), particularly when titanium alloy is used. The ability to produce higher quality parts using EBM technology is making EBM more competitive. After briefly introducing the EBM process and the processing factors involved, this paper reviews recent progress in the processing, microstructure, and properties of titanium alloys and their composites manufactured by EBM. The paper describes significant positive progress in EBM of all types of titanium in terms of solid bulk and porous structures including Ti–6Al–4V and Ti–24Nb–4Zr–8Sn, with a focus on manufacturing using EBM and the resultant unique microstructure and service properties (mechanical properties, fatigue behaviors, and corrosion resistance properties) of EBM‐produced titanium alloys.

     

High‐Entropy Alloys: Potential Candidates for High‐Temperature Applications – An Overview

Multi‐principal elemental alloys, commonly referred to as high‐entropy alloys (HEAs), are a new class of emerging advanced materials with novel alloy design concept. Unlike the design of conventional alloys, which is based on one or at most two principal elements, the design of HEA is based on multi‐principal elements in equal or near‐equal atomic ratio. The advent of HEA has revived the alloy design perception and paved the way to produce an ample number of compositions with different combinations of promising properties for a variety of structural applications. Among the properties possessed by HEAs, sluggish diffusion and strength retention at elevated temperature have caught wide attention. The need to develop new materials for high‐temperature applications with superior high‐temperature properties over superalloys has been one of the prime concerns of the high‐temperature materials research community. The current article shows that HEAs have the potential to replace Ni‐base superalloys as the next generation high‐temperature materials. This review focuses on the phase stability, microstructural stability, and high‐temperature mechanical properties of HEAs. This article will be highly beneficial for materials engineering and science community whose interest is in the development and understanding of HEAs for high‐temperature applications.     

Mechanical Properties and Interlaminar Fracture Toughness of Glass‐Fiber‐Reinforced Epoxy Composites Embedded with Shape Memory Alloy Wires

The effects of the content and position of shape memory alloy (SMA) wires on the mechanical properties and interlaminar fracture toughness of glass‐fiber‐reinforced epoxy (GF/epoxy) composite laminates are investigated. For this purpose, varying numbers of SMA wires are embedded in GF/epoxy composite laminates in different stacking sequences. The specimens are prepared by vacuum‐assisted resin infusion (VARI) processing and are subjected to static tensile and three‐point‐bending tests. The results show that specimens with two SMA wires in the stacking sequence of [GF₂/SMA/GF₁/SMA/GF₂] and four SMA wires in the stacking sequence of [GF₄/SMA/GF₂/SMA/GF₄] exhibit optimal performance. The flexural strength of the optimal four‐SMA‐wire composite is lower than that of the pure GF/epoxy composite by 5.76% on average, and the flexural modulus is improved by 5.19%. Mode‐I and II interlaminar fracture toughness tests using the SMA/GF/epoxy composite laminates in the stacking sequence of [GF₄/SMA/GF₂/SMA/GF₄] are conducted to evaluate the mechanism responsible for decreasing the mechanical properties. Scanning electron microscopy (SEM) observations reveal that the main damage modes are matrix delamination, interfacial debonding, and fiber pullout.

     

Effect of High‐Energy Ball Milling on Mechanical Properties of the Mg–Nb Composites Fabricated through Powder Metallurgy Process

New biocompatible and biodegradable Mg–Nb composites used as bone implant materials are fabricated through powder metallurgy process. Mg–Nb mixture powders are prepared through mechanical milling and manual mixing. Then, the Mg–Nb composites are fabricated through cold press and sintering processes. The effect of mechanical milling and Nb particles as reinforcements on the microstructures and mechanical properties of Mg–Nb composites are investigated. The mechanical milling process is found to be effective in reducing the size of Mg and Nb particles, distributing the Nb particles uniformly in the Mg matrix and obtaining Mg–Nb composite particles. The Mg–Nb composite particles can be bound together firmly during the sintering process, result in Mg–Nb composite structures with no intermetallic formation, lower porosity, and higher mechanical properties compared to composites prepared through manual mixing. Interestingly, the mechanical properties of manually mixed Mg–Nb composites appear to be even lower than that of pure Mg.

     

Effects of Cu on Microstructures,Mechanical, and Magnetic Properties of Fe–Ni–P Alloys Fabricated by Liquid Phase Sintering

The Fe–Ni–P–Cu alloys with different copper content (0, 0.5, 1, and 2 wt%) are fabricated by liquid phase sintering (LPS) at 950 °C. The nano‐Cu powder is mechanically mixed for 90 min with Fe–Ni–P composite powder using the ethanol as the medium. The microstructure, microhardness and compressive properties of Fe–Ni–P–Cu alloys are investigated. The results indicate that the copper is beneficial to improve the mechanical properties of sintered specimens. The sample contains a small amount of γ‐(Fe, Ni) phase when the copper content is 1 wt%, which results in its the highest compressive yield strength (948.1 MPa). The highest microhardness of 371 HV is accessible in Fe–Ni–P–Cu alloy with 2 wt% Cu. The fracture surface analysis indicates that sintered specimens with Cu addition exhibit a typical intergranular mode.