钛合金异形薄壁壳体铸造工艺数值模拟及优化

为解决钛合金精密铸造产品合格率低、试验优化周期长的问题,以某钛合金异形薄壁件为研究对象,采用逆向工程手段优化浇注系统设计。结合ProCAST有限元分析软件确定铸件缺陷分布位置,依据铸件缩松分布情况对铸造方案进行迭代优化,解决铸件承力板区域缩孔问题。根据优化结果进行生产验证,结果表明,钛合金铸件采用真空熔模铸造方案,铸件上、下端分别设置3处浇/冒口时,模拟结果显示铸件凝固过程整体温度分布合理,铸件中的缩孔均被优化剔除。该工艺方案可行性高,试制件无损检测结果与数值模拟结果吻合度高,铸件成形质量、冶金质量均达到预期效果。     

力-磁-环境耦合作用下超磁致伸缩材料TbDyFe表面畴变的观察

就TbDyFe超磁致伸缩材料在应力、磁场和环境耦合作用下的表面畴变进行了研究。主要利用光学显微镜及其微分干涉相衬显微（Differential Interference Contrast，DIC）系统，并自行设计搭建了恒磁场试样台和环境试验箱，由此实现了对应力、磁场及环境作用下材料表面磁畴变化的原位跟踪研究。     

The dielectric properties of epoxy/AlN composites

In this paper, AlN ceramic powder is chosen to be mixed with epoxy to form epoxy/AlN composites, the effects of the content of AlN filler on the physical and dielectric properties of epoxy/AlN composites are developed. From the SEM observation, the particles of self-synthesized AlN powder, obtained by using combustion method, is less uniformity and the average particle size is about 3.12 μm. Only the AlN phase can be detected in the XRD patterns of the epoxy/AlN composites. The more AlN powder is mixed with epoxy, the higher crystal intensity of AlN phase will exist in the XRD patterns. As the content of AlN powder in the epoxy/AlN composites increases from 5 to 40 wt.%, the dielectric constant increases from 6.52 to 7.28 (measured at 1 MHz). The loss tangent of epoxy/AlN composites is slightly increased as the measured frequency increases. Moreover, the epoxy/AlN composites in this investigation show less pores as compared to other literatures. The results indicate that the fabrication process has an apparent effect on the decrease of porosities, and the composites with a low porosity will lead to a low loss tangent.     

Extraction and preparation of bamboo fibre-reinforced composites

Natural plant fibre composites have been developed for the production of a variety of industrial products, with benefits including biodegradability and environmental protection. Bamboo fibre materials have attracted broad attention as reinforcement polymer composites due to their environmental sustainability, mechanical properties, and recyclability, and they can be compared with glass fibres. This review classifies and describes the various procedures that have been developed to extract fibres from raw bamboo culm. There are three main types of procedures: mechanical, chemical and combined mechanical and chemical extraction. Composite preparation from extracted bamboo fibres and various thermal analysis methods are also classified and analysed. Many parameters affect the mechanical properties and composite characteristics of bamboo fibres and bamboo composites, including fibre extraction methods, fibre length, fibre size, resin application, temperature, moisture content and composite preparation techniques. Mechanical extraction methods are more eco-friendly than chemical methods, and steam explosion and chemical methods significantly affect the microstructure of bamboo fibres. The development of bamboo fibre-reinforced composites and interfacial adhesion fabrication techniques must consider the type of matrix, the microstructure of bamboo and fibre extraction methods.     

Study on low temperature brazing of magnesium alloy to aluminum alloy using Sn–xZn solders

In this article, a series of Sn–xZn solders are designed for joining Mg/Al dissimilar metals by low temperature brazing. The effect of Zn content in Sn–Zn solders on microstructure evolution and mechanical properties of the different brazed joints are investigated. The experimental results indicate that Sn–30Zn alloy is identified as the optimized solder. Al–Sn–Zn solid solutions form and disperse in the brazing zone of the Mg/Sn–30Zn/Al brazed joint, decreasing the risk of embrittlement of the brazed joint. The average shear strength of Mg/Sn–30Zn/Al brazed joint can reach 70.73 MPa. The joint fractures in the coarse blocky Mg₂Sn intermetallic phases in the center of the brazing zone.     

Meso-scale analysis of the creep behavior of hydrogenated Zircaloy-4

During dry storage, creep is the most likely degradation mechanism for spent Zircaloy fuel cladding. The fuel cladding integrity during dry storage depends on the amount of oxidation, irradiation hardening and hydrogen-uptake during in-reactor operation. In this paper, the effect of hydrogen on the creep behavior of Zircaloy-4 cladding material was investigated at different temperatures. Depending on temperature, hydrogen can be found in the sample in solid solution and/or hydride. To capture this phenomenon, a numerical mesoscale model of the hydrogenated material has been built using the Finite Element (FE) Method. The numerical setup explicitly describes the hydrides as an inclusion in a hydrogenated Zircaloy-4 matrix. The matrix creep behavior follows a combined Norton-Bailey and Norton creep rules whereas the hydrides are considered to be elastic material. The creep law was defined in FE Code ABAQUS using the user subroutine CREEP. The comparison of predicted creep behavior obtained from numerical modeling showed good agreement with the results reported in literature. The predicted creep behavior shows a significant effect of hydrides morphology. Particularly, our model is able to seize the competition between the creep strain rate enhancement induced by hydrogen in solid solution and its reduction due to precipitated hydrogen.     

Preparation and properties of porous ceramic aggregates using electrical insulators waste

In this paper, porous ceramic aggregates were prepared by electrical insulators waste (EIW). Effects of sintering temperature and content of EIW on the aggregates’ properties such as bulk density, and apparent porosity, total porosity, and cold crushing strength were investigated. With increasing sintering temperature and content of EIW, bulk density and cold crushing strength of the aggregates increased, apparent porosity and total porosity decreased. Based on these results, total porosity of specimens in group B sintered at 1200 °C is 62.0%, cold crushing strength is 35.3 N, and thermal conductivity is 0.165 W/(m K) at 300 °C. Comprehensive properties of specimens can be optimized by adjusting sintering temperature. Meanwhile, strength variation resulted from the combined effects of phase transformation and matrix densification under different sintering temperatures.     

Enhancement in the photocatalytic and optoelectronic properties of erbium oxide by adding zinc oxide and molybdenum

Rare earth metals like erbium oxide (Er₂O₃) show outstanding photocatalytic properties. However, its high recombination rate and low surface area limit its performance. Therefore, various metal oxide composites with Er₂O₃ have been reported to improve their photocatalytic and optoelectronic properties. In this study, a composite of Er₂O₃ and zinc oxide (ZnO) was synthesized using the sol-gel combustion method to enhance its surface area. Moreover, molybdenum (Mo) was loaded on the matrix to suppress the charge recombination. The detailed characterizations were conducted by employing X-ray Diffraction (XRD), Raman Spectroscopy, Field Emission Scanning Electron Microscopy (FESEM), Brunauer–Emmett–Teller (BET) analysis, Photoluminescence (PL) spectroscopy and UV–Vis spectroscopy. BET analysis revealed the enhancement in surface area by adding ZnO and Mo (from S_BET = 29.07 m²/g to S_BET = 45.71 m²/g). Additionally, the loading of Mo enhanced the immobilization of carriers that facilitate the photooxidation process and suppressed the electron-holes recombination (from 800 counts to 100 counts) as confirmed by the PL spectroscopy. Photocatalytic studies were comparatively analyzed by degradation of textile dye named methylene blue (MB). The efficiency of Er₂O₃ improved by up to 80% by adding the ZnO and Mo. The composite of Er₂O₃ with ZnO and loading of Mo, not only improved the photocatalytic properties but also improved the electrical properties of the Er₂O₃ (σ = 4.4 × 10⁻⁴ Sm⁻¹ to σ = 5.1 × 10⁻⁴ Sm⁻¹) as confirmed by the Hall Effect. Due to enhancement in properties, the proposed material can be rendered as one of the most suitable candidates for optoelectronic applications.     

High-entropy (Ho0.2Y0.2Dy0.2Gd0.2Eu0.2)2Ti2O7/TiO2 composites with excellent mechanical and thermal properties

High-performance ceramics with low thermal conductivity, high mechanical properties, and idea thermal expansion coefficients have important applications in fields such as turbine blades and automotive engines. Currently, the thermal conductivity of ceramics has been significantly reduced by local doping/substitution or further high-entropy reconfiguration of the composition, but the mechanical properties, especially the fracture toughness, are insufficient and still need to be improved. In this work, based on the high-entropy titanate pyrochlore, TiO₂ was introduced for composite toughening and the high-entropy (Ho_0.2Y_0.2Dy_0.2Gd_0.2Eu_0.2)₂Ti₂O₇-xTiO₂ (x = 0, 0.2, 0.4, 1.0 and 2.0) composites with high hardness (16.17 GPa), Young's modulus (289.3 GPa) and fracture toughness (3.612 MPa·m^0.5), low thermal conductivity (1.22 W·m⁻¹·K⁻¹), and thermal expansion coefficients close to the substrate material (9.5 ×10⁻⁶/K) were successfully prepared by the solidification method. The fracture toughness of the composite toughened sample is 2.25 times higher than that before toughening, which exceeds most of the current low-thermal conductivity ceramics.