Influence of different solvents on the structural, optical and morphological properties of CdS nanoparticles

CdS is one of the most important II-VI semiconductors, with applications in solar cells, optoelectronics and electronic devices. CdS nanoparticles were synthesized via microwave-assisted solvothermal technique. Structural and morphological characterization revealed the presence of crystalline structures presenting single phase with different morphologies such as “nanoflowers” and nanoplates depending on the solvent used. Optical characterization was made by diffuse reflectance and photoluminescence spectroscopy, revealing the influence of the different solvents on the optical properties due to structural defects generated during synthesis. It is proposed that these defects are related to sulfur vacancies, with higher concentration of defects for the sample synthesized in ethylene glycol in comparison with the one synthesized in ethylene diamine.     

不同正火工艺对钢板力学性能的影响

试验研究了含Nb、V、Ti微合金元素的低合金钢板采用880、900、920 ℃不同正火温度及不同保温时间热处理后的力学性能和金相组织,结果表明：在合适的温度范围内,适当延长保温时间,在细化晶粒的同时,还可以消除内部偏析现象和带状组织等缺陷,最终使钢板获得优异的综合力学性能。     

铝基复合材料无损检测研究进展

介绍了铝基复合材料的基本性能、应用情况以及缺陷类型,分析了缺陷产生的原因以及缺陷对铝基复合材料性能的影响,对各种无损检测技术在该领域的适用特点进行了比较,综述了液体渗透法、超声波检测法、射线检测法在铝基复合材料无损检测中的实际应用。     

The Influence of Grain Boundaries on Radiation-Induced Point Defect Production in Materials: A Review of Atomistic Studies

Radiation-induced defects cause severe degradation of materials properties during irradiation that can ultimately cause the material to fail. Consequences of these defects include swelling, embrittlement, and undesirable phase transformations. Nanocrystalline materials, which contain a high density of grain boundaries, have demonstrated enhanced radiation tolerance compared to large grain counterparts under certain conditions. This is because, as has long been recognized, grain boundaries can serve as defect sinks for absorbing and annihilating radiation-induced defects. Increasingly, researchers have examined how grain boundaries influence the direct production of defects during collision cascade, the origin of the radiation-induced defects. In this review article, we analyze the computational studies in this area that have been performed during the past two decades. These studies examine defect production near grain boundaries in metallic, ionic, and covalent systems. It is found that, in most systems, grain boundaries absorb more interstitials than vacancies during the defect production stage. While this is generically true of most boundaries, the detailed interaction between defects and grain boundaries does depend on boundary atomic structure, the stress state near the boundary, cascade-boundary separation, and materials properties. Furthermore, the defect distribution near boundaries is qualitatively different from that in single crystals, with the former often exhibiting larger vacancy clusters and smaller interstitial clusters than the latter. Finally, grain boundaries that are damaged after cascades have occurred exhibit different interaction behavior with defects than their pristine counterparts. Together, these atomistic simulation results provide useful insight for both developing higher-level modeling of defect evolution at long timescales and how interfaces influence radiation damage evolution.     

20CrNiMo牙轮牙爪锻造缺陷对力学性能的影响

KX-250三牙轮钻头上的牙轮牙爪可选用20CrNiMo钢锻造,但20CrNiMo牙轮牙爪在锻造过程中产生的缺陷严重影响产品的力学性能.为此对20CrNiMo牙轮牙爪进行质量跟踪,并对试样进行了力学性能的测试.结果表明：当锻造产生了白点和过热缺陷时,牙轮牙爪的力学性能明显下降,尤其是塑性指标和冲击韧度降低明显.为了防止这些缺陷的产生,还提出了一些对策,以提高牙轮牙爪的力学性能.     

搅拌摩擦焊接缺陷的补焊方法

搅拌摩擦焊接方法在某些条件下也会造成焊接缺陷的产生,其中对接头性能有显著影响的缺陷包括沟槽、孔洞和未焊合.针对这三种类型的缺陷,用搅拌摩擦焊接方法进行补焊,以此研究补焊接头的焊缝成形和力学性能.结果表明,采用搅拌摩擦补焊方法能够消除沟槽、孔洞和未焊合等搅拌摩擦焊接缺陷;在优化的补焊工艺参数下,能够获得焊缝成形良好的补焊接头,其性能与优质原始接头的性能相当;补焊接头在拉伸测试中均在焊缝的后退侧发生断裂,拉伸断口具有明显的韧窝特征.     

Fatigue properties of TiAl alloys

The fatigue properties of TiAl alloys, namely fatigue life, cyclic stress–strain behaviour and fatigue crack growth resistance are reviewed in the present paper. The influence of different parameters (microstructure, defects, temperature and environment) on these properties is examined. Finally, some considerations on the fatigue reliability of TiAl components are proposed.     

Bifilm defects in ductile-iron support bracket castings

Many filling defects such as bi-film defect, gas bubble, loosed sand and etc., are developed by turbulent filling. These defects entrapped and flowed along mold cavity during the filling process. As a result, they makes casting property unreliable and unpredictable. The best way to prevent the filling defect is to control the gating velocity under a critical value using a bottom gating runner system. Two different gating system, top- and bottom- systems, are applied for casting ductile-iron support bracket. For these two runner systems, their filling defects are predicted by a numerical modeling. Two- and three- parameter Weibull probability are plotted to analyze the reliabilities of the mechanical properties of the castings from these two gating systems. A good and reliable runner system for casting a high elongation and fracture toughness of the support bracket was proposed in this study.     

Cu-Cr-Zr合金铸锭铸造缺陷产生原因与防止措施

铸锭的铸造质量对合金的使用性能有重大影响,Cu-Cr-Zr合金常见的铸造缺陷包括缩孔、气孔、裂纹、偏析、冷隔和铜豆等。通过对比不同工艺条件下铸锭的微观组织,讨论了熔铸工艺参数以及模具预处理状态对Cu-Cr-Zr合金铸锭铸造质量的影响,并分析了较高含量合金元素所造成的枝晶偏析以及成分偏聚对合金性能的影响。分析了铸造缺陷的产生原因及其对合金性能的影响,介绍了防止常见铸造缺陷的措施和工艺方法。     

铝合金薄板搅拌摩擦焊搭接界面缺陷与接头性能

针对2A12–T4铝合金薄板进行了搅拌摩擦焊搭接试验,研究了焊接参数对缺陷形态与接头性能的影响规律. 结果表明,勾状缺陷具有更大的高度和弯曲角度,最大缺陷高度为上板厚度的12.7%. 随焊接速度增大,缺陷高度减小.随转速提高,勾状缺陷高度先增加后减小,冷搭接缺陷高度呈“V”形变化. 在950 r/min,200 mm/min下接头强度最高,接头系数可达84%. 维氏显微硬度分布呈“W”形,上板出现接头软化,焊核区下部硬度高于上部硬度. 冷搭接缺陷是影响接头性能的主要因素,由于有效搭接宽度较小,接头断裂方式为沿搭接面的剪切断裂.     

Non-standard tests for process control in chemically bonded sands

Chemically bonded sand cores and molds are more commonly referred to as precision sand systems in the high production automotive powertrain sector. Their behavior in contact with molten metal can lead to casting defects. Consequently, the interaction is of great interest and an important part of metal casting technology. The American Foundry Society(AFS) sand testing is based on physical, mechanical, thermal and chemical properties of the sand system. Foundry engineers have long known that certain AFS sand tests provide limited information regarding control of molding and casting quality. The inadequacy is due to the fact that sand casting processes are inherently thermo-mechanical, thermo-chemical and thermo-physical. Non-standard foundry sand testing has proven useful for laboratory measurement of these characteristics in foundry sand using a disc-shaped specimen. Similarly, the equivalent disc-shaped specimens are used for casting trials. In order to accomplish near-net-shape casting with minimal defects, it is necessary to understand both the properties of the sand system, as well as the interface of molten metal when different binders, additives and/or refractory coatings are used. The methodology for the following non-standard chemically bonded sand tests is described:(1) disc transverse;(2) impact;(3) modified permeability;(4) abrasion;(5) thermal distortion;(6) quick loss on ignition. The data related to the non-standard sand tests were analyzed and interpreted. The test results indicate that there is relatively lower test-to-test variability with the disc-shaped specimens. The non-standard tests were able to discriminate between the chemically bonded polyurethane cold box sand specimens. Further studies should be conducted on various other sand and binder systems as well as on different specimen thicknesses.     

电弧离子镀TiN薄膜中的缺陷及其形成原因*

分析了电弧离子镀（ALP）TiN薄膜中的主要缺陷-熔滴、孔洞和疏松等。结果表明：这些缺陷存在于晶内、晶界或者贯穿于整个薄膜；缺陷的存在极大地影响了薄膜的性能；缺陷密度与镀膜方法及具体的工艺参数有密切关系；使用磁过滤器镀制薄膜可显著减少上述缺陷，从而提高薄膜的各种性能。认为使用磁过滤器镀制TiN及其各种复合或多层薄膜是一种切实有效的方法，是今后制备高性能TiN及其复合膜的发展方向，另外，缩短脉冲电弧在高值时的时间，用人工来减少薄膜缺陷也是一种行之有效的方法。     

挤压变形程度对2A50合金组织性能的影响

通过试验的方法在不同变形程度等条件下对2A50合金进行性能测试和金相分析，结果表明经过挤压变形后，2A50合金晶粒被细化，纵向组织被拉长，铸造缺陷改善，力学性能提高。     

RuAl and its alloys. Part I. Structure,physical properties,microstructure and processing

The structure, physical properties, processing and the related microstructure of RuAl and its alloys are presented in Part I of this overview, with a particular emphasis on the recent studies. The structure and physical properties reviewed include electronic structure, bonding, crystal structure, phase stability, as well as thermodynamic, elastic, electrical and thermal properties. Crystal defects are also covered and special attention is given to constitutional point defects, dislocations and planar faults. Ingot and powder metallurgy, mechanical alloying and thin film deposition are considered as processing techniques for the production of single or multiphase RuAl alloys. The typical characteristics of the microstructure related to different processing methods are presented. The entire overview is completed in Part II where mechanical properties, deformation and fracture behavior, environmental resistance and applications are discussed.     

Effect of casting practice on the reliability of Al cast alloys

Abstract:

The properties of aluminium castings are strongly affected by their inclusion content, particularly entrained surface alumina films. These form due to the surface turbulence associated with mould filling, which causes the oxidised surface of a liquid metal to fold-over onto itself and be submerged into the bulk liquid with a thin layer of air entrapped within it. This is known as entrainment action. These flaws have been reported to increase the variability of the fracture strengths of Al alloy castings. This means that shape castings in light alloys can have inconsistent properties, which makes designing structures employing shape castings more difficult. Entrained surface layers can cause premature failure, but also have been associated with other defects, such as hydrogen porosity, shrinkage porosity, intermetallic compounds and hot tearing. Recent research has suggested that the air inside the defect would react with the surrounding melt leading to its consumption, which may enhance the mechanical properties of the casting. In this work, liquid aluminium was poured into three identical ceramic moulds which were immediately placed in a furnace to preserve the molten metal at 800 °C, for different periods of time prior to freezing. The Weibull moduli of the plate castings were determined under tensile conditions, and their fracture surfaces examined using SEM. Investigation of the fracture surfaces of the specimens detected many alumina layers at different locations. Many of which were found inside pores, reflecting the role of entrained defects in the formation of porosity. The results also suggested that opposite phenomena may take place during the holding treatment. The consumption of air inside the entrained defects due to reaction with the surrounding molten metal may lead to improvements in mechanical properties, but this may be accompanied by hydrogen passing into the defects, which has a deleterious effect on properties.     

Filament-Level Modeling of Aramid-Based High-Performance Structural Materials

Molecular statics and molecular dynamics are employed to study the effects of various microstructural and topological defects (e.g., chain ends, axial chain misalignment, inorganic solvent impurities, and sheet stacking faults) on the strength, ductility, and stiffness of p-phenylene terephthalamide (PPTA) fibers/filaments. These fibers can be considered as prototypes for advanced high strength/high-stiffness fibers like Kevlar^®, Twaron^®, New Star^®, etc. While modeling these fibers, it was taken into account that they are essentially crystalline materials consisting of stacks of sheets, with each sheet containing an array of nearly parallel hydrogen-bonded molecules/chains. The inter-sheet bonding, on the other hand, was considered as mainly being of van der Waals or p-electron character. The effects of various deviations of the PPTA fiber structure from that of the perfectly crystalline structure (i.e., microstructural/topological defects) on the material’s mechanical properties are then considered. The results obtained show that while the presence of these defects decreases all the mechanical properties of PPTA fibers, specific properties display an increased level of sensitivity to the presence of certain defects. For example, longitudinal tensile properties are found to be most sensitive to the presence of chain ends, in-sheet transverse properties to the presence of chain misalignments, while cross-sheet transverse properties are found to be most affected by the presence of sheet stacking faults.     

Defects and transport properties of metal oxides

The paper gives an overview of different types of defects and defect structures in metal oxides and transport properties such as diffusion and electrical conductivity. Point defects (vacancies, interstitials, impurity and dopant ions, hydrogen ions, a.o.) and corresponding defect structures are described by defect equations and equilibria. Oxides of common use metals and which are of particular interest in many aspects of high-temperature oxidation of metals, e.g., cobalt and nickel oxides, chromia, alumina and silica, are used as examples in describing defect structures and transport properties.     

铝合金铸件中的凝固缺陷形成机理及预测

孔洞与热裂是铸件在凝固过程中最常遇到的典型缺陷。两者均形成于合金凝固末期,与液相补缩不足相关,但又有各自的形成机理。铝合金熔体对氢气有很大的溶解度,凝固过程中又因为溶解度的剧降而析出。孔洞是液相中过饱和的气体压力与凝固收缩引起的压力降共同作用的结果。热裂则是在凝固末期由于铸件收缩受阻而产生的应力以及液相补缩不足而导致的,其不仅与合金性质、铸造条件有关,并且受铸件形状的影响。文章基于近年来该方面的理论研究成果,总结了关于孔洞与热裂的形成机理以及几种目前所应用的经典预测模型,并对这几种模型的理论基础以及所考虑的关键参数进行了分析与讨论,在此基础上提出了未来新模型的研究方向和亟需解决的关键问题。     

Influence of annealing on the structural and optical properties of ZnO films grown by MOCVD

The properties of ZnO films grown on Si (1 1 1) substrates by Metal-Organic Chemical Vapor Deposition technique using diethylzinc and H₂O as reactant gases are reported. The primary focus is on understanding the origin of deep-level luminescence. As increasing the annealing temperature, a visible emission is observed both in samples annealing in oxygen atmosphere and nitrogen atmosphere. In addition, this broad defect emission becomes obviously asymmetric when the annealing temperature was increased to 1000 °C in oxygen atmosphere. Theoretical investigations have reported that the formation enthalpy of defects is varied under different conditions. With these results, it is suggested that the visible emission in ZnO films annealed in oxygen atmosphere is related to zinc vacancy and oxygen interstitial defects. While, the green emission in ZnO films which were annealed in nitrogen atmosphere is attributed to oxygen vacancy defects.     

Effect of crystallite size on structural and luminescent properties of nanostructured Eu:KGdF4 synthesised by co-precipitation method

The Eu³⁺:KGdF₄ powders with average crystallite size of 20 and 25 nm have been obtained from solution by co-precipitation method. Morphology of the as-received powders was examined by XRD and TEM methods. Behaviour of these two powdered batches, characterised by different size of nanocrystallites, versus thermal treatment has been studied by X-ray powder diffraction, thermogravimetric, infrared spectroscopy and emission spectroscopy methods. The phase transitions between low-temperature cubic, orthorhombic, trigonal and high-temperature cubic modifications of KGdF₄ were detected for both samples heated in 300–790 °C temperature range. Abundance of the particular polymorphic form observed at given temperature differs considerably for samples of different initial crystallite size. Besides, significant differences in number of lattice defects, water contents and emission properties were observed for these two samples. The properties of material precipitated from solution are also compared with structural and optical properties of the Eu³⁺:KGdF₄ fluoride synthesised by a solid-state reaction.