Influence of crystal orientation on cellular growth of a nickel-base single crystal superalloy

The cellular pattern evolution during directional solidification of a nickel-base single crystal superalloy has been studied in different crystallographic orientations using re-oriented seed crystals. Under the same thermal gradient and solidification velocity, the microstructures of differently oriented cellular single crystals are schematically investigated. It is concluded that the cellular growth direction is less affected by the seed orientation and depends on the heat flow, and is usually along heat flow direction. Cellular interface stability and microstructure are greatly influenced by the crystallographic orientation. When increasing the misorientation, the cell spacing increases correspondingly and the cellular growth interface becomes more unstable.     

ITER校正场线圈盒真空电子束焊接分析

校正场线圈是ITER大型超导磁体系统的重要组成部分,在线圈盒焊接过程中,若线圈盒内表面与对地绝缘接触部分的温度过高,将影响校正场线圈的超导绝缘性能。文中应用有限元焊接模拟软件SYSWELD对线圈盒的电子束焊接过程进行了数值模拟,利用双椭球热源与3D高斯热源的组合热源模拟真空电子束焊独有的钉形热源,得到了与实际较为相符的熔池形貌;确定了接触点上的温度分布,并分析其对校正场线圈的影响;同时,对比了不同线圈盒结构的温度场分布,从而得到能够保护对地绝缘的合理肩部尺寸。     

A proton-conducting composite membrane: Sn0.95Al0.05P2O7 and polystyrene-b-poly(ethylene/propylene)-b-polystyrene

An anhydrous proton conductor, Sn_0.95Al_0.05P₂O₇ (SAPO), composed of polystyrene-b-poly(ethylene/propylene)-b-polystyrene (SEPS), was developed and characterized using morphological, structural, and electrochemical analyses. In the composite membrane with 20 wt% SEPS, a homogeneous distribution of SAPO particles in the matrix was obtained in the thickness range of 65-90 μm, yielding a proton conductivity of 3.4 × 10⁻³ S cm⁻¹ at 200 °C, tensile strength of 4.6 MPa and an elongation at break of 711.0% at room temperature. Fuel cell tests verified that the open-circuit voltage was maintained at a constant value of approximately 1 V between 100 and 250 °C. The peak power densities achieved with unhumidified H₂ and air were 77.0 mW cm⁻² at 100 °C, 121.0 mW cm⁻² at 150 °C, and 163.1 mW cm⁻² at 225 °C.     

超导电性及其材料的应用与进展

超导的发现是20世纪物理学的一项伟大成果。文章主要阐述了超导现象,超导电性的理论研究、新进展,超导材料的主要制备技术,以及对超导体新的应用领域提出了一些展望。随着高温超导材料的开发成功,超导材料将越来越多地应用于尖端技术中,因此超导材料技术有着重大的应用发展潜力,可解决未来能源、交通、医疗和国防事业中的重要问题。     

Temperature-Dependent Compressive Deformation Behavior of Commercially Pure Iron Processed by ECAP

To explore the temperature dependence of deformation behavior of BCC structural materials and the relevant effect of pre-annealing, commercially pure iron(CP Fe) produced by equal-channel angular pressing(ECAP) is selected as the experimental material. The influences of deformation temperature T and pre-annealing on deformation behavior,surface deformation characteristics and substructures of ECAP Fe were systematically studied. The results show that ECAP Fe undergoes a remarkable strain softening stage after a rapid strain hardening during uniaxial compression, and the softening degree and the yield strength rYSfirst decrease and then increase with raising temperature. Pre-annealing at400 °C effectively weakens the strain softening degree and increases rYS. To understand the influence of deformation temperature on deformation behavior, as well as the relevant pre-annealing effect, deformation and damage characteristics and dislocation structures are studied in detail. In a word, the strain softening of ECAP Fe is associated not only with internal structural instability, but also with temperature, and pre-annealing at 400 °C improves high-temperature mechanical properties of ECAP Fe.     

量子模拟的研究现状与进展

介绍量子模拟的基本概念、理论、方法及其应用领域,综述可用于量子模拟的物理系统——原子、光子、离子、电子和核自旋等系统的研究进展,并就量子模拟的未来研究方向及发展趋势进行分析。     

Synthesis,structure, and properties of silicon oxycarbide aerogels derived from tetraethylortosilicate /polydimethylsiloxane

Porous silicon oxycarbide (SiCO) aerogel monoliths were prepared by the sol-gel method using Tetraethylortosilicate/Polydimethylsiloxane as organic-inorganic precursors. The precursor gels were dried by supercritical ethanol fluid and pyrolyzed at 1200 °C in nitrogen atmosphere to form SiCO aerogels. The as-prepared SiCO aerogels are amorphous and present a network microstructure, surface area of 198.04 m²/g, average pore diameter of 56 nm, and pore volume of 0.648 cm³/g. The thermal conductivity of aerogel monoliths is only 0.027 W/m·K at 25 °C (Hot disk method). The atom ratios of Si, C, O elements in the SiCO aerogels are 30.77%, 14.67%, 54.56% respectively. The network microstructure of the SiCO aerogels are retained until 1100 °C, and the chemical groups and crystal phase structures are kept up until 1200 °C. There is only 1.65% of weight-loss until the same heated at 1200 °C in air, which is one of the highest thermally stable temperatures for SiCO aerogels ever reported.     

LOW TEMPERATURE MAGNETIC FORCE MICROSCOPY STUDY OF VORTEX IN A YBa_2Cu_3O_(7-x) THIN FILM

A low temperature magnetic forc micro-scope for the study of high temperature superconductor isdeveloped. It has been applied to spatially resolve singlevortices at low temperature (77K) in a YBa_2Cu_3,O_(7-x). thinfilm deposited by laser ablation on a NdGaO_3 substrate.The images of disordered vortex arrangements are obtained. The movement of single vortices after a contactmode scanning of the detecting tip over the thin film sur-face is observed. The reason for the movement is dis-cussed.     

Room- and high-temperature flexural strength of a stable solid oxide fuel/electrolysis cell sealing material

The structural integrity of the sealing material is critical for the reliability of solid oxide fuel/electrolysis stacks. The current work concentrates on microstructural and mechanical aspects of a sealant material for this application. In particular, the crystallization behavior as a determining factor for the sealants’ mechanical behavior is investigated via high-temperature XRD for 24?h. Furthermore, regarding mechanical properties, three- and four-point bending tests are carried out on sealant bars and head-to-head joined specimens at room- and high-temperatures, yielding in particular relevant fracture stress data. In addition, the elastic modulus is measured by the impulse excitation test from RT to 900?ºC. Tests are done for both as-sintered (as-joined) and annealed samples. The main crystallization appears to happen during the initial joining time. The sealant shows a relatively stable flexural strength in terms of temperature dependency as well as effects of the aging process. In fact, the joined specimens reveal a more than 50% lower flexural strength than glass bars at all temperatures. A complementary finite element simulation indicates the presence of a non-negligible thermal residual stress in joined specimens.     

Thermal shock damage assessment of a BNW/SiO2 ceramic: Insight from temperature-dependent material properties

The high-temperature service performance of nearly fully dense 20 wt% BN_W/SiO₂ ceramic was systematically investigated. The oxidation damage and strength degradation of the whiskers combined with the surface microstructures of the samples predominantly influence the flexural strength from RT to 1000 °C. In previous work, the temperature dependence of the material properties is invariably ignored when evaluating thermal stress crack initiation and propagation behaviour. In this work, modified thermal shock models that include temperature-dependent material properties were established based on thermal-shock fracture (TSF) theory and thermal-shock damage (TSD) theory. Then, the thermal shock resistance (TSR) of the BN_W/SiO₂ ceramic was evaluated by preforming a water quenching test. The modified models could better explain the TSR behaviour of the ceramic, indicating that considering the temperature-dependent material properties will reveal the thermal shock damage mechanism more precisely.