Orientation dependent behavior of tensile-creep deformation of hot rolled Ti65 titanium alloy sheet

The mill products like sheet always have one or more severe textures inevitably,and its effect on mechan-ical properties is not a negligible issue.The orientation dependent tensile-creep behavior induced by rolling texture of Ti65 titanium alloy sheet has been systematically investigated at 650℃.There are some anisotropic characteristics between TD and RD of Ti65 sheet.The UTS and TYS of TD are higher than RD at 650℃.Besides,the creep endurance time of TD(172.6-174.5 h)is about three times longer than RD(55.6-65.1 h)at 650℃and 240 MPa.Moreover,the grains are inclined to form Texture Ⅲ(1 2(1)6)[1(2)11]and(01(1)3)[1(2)11]after creep along with TD,but to form Texture I((1)2-(1)0)[10-(1)0]after creep along with RD.Finally,the crack initiation site is different during creep in TD and RD.The reason for anisotropic properties of tensile and creep has been summarized in two aspects:(ⅰ)the change of the SFs(Schmid factors)value between TD and RD;(ⅱ)the difference of creep mechanism between TD(grain boundary sliding)and RD(dislocation slip).Anisotropy of Ti65 sheet should be fully considered to increase structural efficiency in the engineering design and application.     

Performance of dye-sensitized solar cell fabricated using titania nanoparticles calcined at different temperatures

Synthesis of titania (TiO₂) nanoparticles by sol-gel method and their calcination at different temperatures, viz 450 °C, 550 °C and 650 °C (defined as T450, T550 and T650) has been done. Structural analysis indicates that the T450 sample possesses anatase phase. The phase transformation to rutile starts occurring at T550, and, on increasing the calcination temperature, the crystallization and percentage of rutile phase increases. As the temperature increases from 450 to 650 °C, the crystallite size increases by about a factor of two from 11.5 to 20.2 nm. From SEM micrographs, T550 electrode has been found to have appropriate aggregation, which led to enhanced dye desorption, as compared to T450 and T650 based electrodes. TEM images of the synthesized nanoparticles reveal that the particle size increases from 7 to 28 nm on increasing the calcination temperature from 450 to 650 °C. From the photoluminescence and Fourier transform infrared studies, it has been concluded that the surface OH^? groups are reduced on calcination, which affects the electron injection efficiency. The dye sensitized solar cell, fabricated using T550 sample, having a ratio of anatase/rutile 89:11, has been found to achieve the highest conversion efficiency.     

Anomalous steam oxidation behavior of a creep resistant martensitic 9 wt. % Cr steel

The efficiency of thermal power plants is currently limited by the long-term creep strength and the steam oxidation resistance of the commercially available ferritic/martensitic steel grades. Higher operating pressures and temperatures are essential to increase efficiency but impose important requirements on the materials, from both the mechanical and chemical stability perspective. It has been shown that in general, a Cr wt. % higher than 9 is required for acceptable oxidation rates at 650 °C, but on the other hand such high Cr content is detrimental to the creep strength. Surprisingly, preliminary studies of an experimental 9 wt. % Cr martensitic steel, exhibited very low oxidation rates under flowing steam at 650 °C for exposure times exceeding 20,000 h. A metallographic investigation at different time intervals has been carried out. Moreover, scanning transmission electron microscopy (STEM) analysis of a ground sample exposed to steam for 10,000 h at 650 °C revealed the formation of a complex tri-layered protective oxide comprising a top and bottom Fe and Cr rich spinel layer with a magnetite intermediate layer on top of a very fine grained zone.     

The Influence of a Magnetic Field on Anomalous Electron Transport in a Quasi-Two-Dimensional Electron System over Liquid Helium

No Heading The magnetoresistance _xx in a quasi-two-dimensional electron system over liquid helium has been measured for magnetic fields up to 2 T in the temperature range 0.5 – 1.7 K. It has been shown that the behavior of the value of _xx as a function of a magnetic field B in the temperature region 1.2 – 1.7 K and at temperature T < 0.9 K is different. At high temperatures the negative magnetoresistance is observed due to weak localization of carriers, at T < 0.9 K the _xx increases monotonically under increasing B. It is supposed that such a difference in the behavior of the _xx is connected with the different character of the electron scattering: elastic at high temperatures, in the region of gas scattering, and inelastic at low temperatures. The last effect gives an additional evidence either for spatial ordering of electrons or for the formation of electron polarons in quasi-two- dimensional channels.PACS numbers: 73.20.Dx; 73.90.+f     

Superlinear dose dependence of high temperature thermoluminescence peaks in Al2O3:C

We report on strong superlinearity of high temperature (300-700 degrees C) thermoluminescence (TL) peaks in alpha-Al2O3:C powder. The main dosimetric peak at approximately 200 degrees C, previously found to exhibit slight superlinearity, is now shown to yield a slope of approximately 1.15 on a log(intensity) vs. log(dose) curve. Higher temperature peaks at approximately 320, 450 and 650 degrees C, previously reported following UV and X-ray excitation, have now been observed after beta irradiation and showed stronger superlinearity. Using a blue filter, the weak peak at approximately 320 degrees C started about quadratically and the slope on the log-log scale decreased gradually from 2 to about unity at approximately 100 Gy. The two higher temperature peaks at approximately 450 and approximately 650 degrees C also exhibited a strong superlinear dose dependence in this dose range, with an average slope of approximately 2. Roughly similar behaviour has been found when a UV filter was used. The possible explanation of the strong superlinearity is discussed.     

Thermal-induced intermixing effects on the optical properties of long wavelength low density InAs/GaAs quantum dots

The effect of post-growth rapid thermal annealing on the photoluminescence properties of long wavelength low density InAs/GaAs (001) quantum dots (QDs) with well defined electronic shells has been investigated. For an annealing temperature of 650 °C for 30 s, the emission wavelength and the intersublevel spacing energies remain unchanged while the integrated PL intensity increases. For higher annealing temperature, blue shift of the emission energy together with a decrease in the intersublevel spacing energies are shown to occur due to the thermal activated In–Ga interdiffusion. While, this behaviour is commonly explained as a consequence of the enrichment in Ga of the QDs, the appearance of an additional exited state for annealing temperatures higher than 650 °C suggests a variation of the intermixed QDs's volume/diameter ratio toward QDs's enlargement.     

On Optimizing Batch Annealing for the Production of IF Steels

Batch annealing characterized by a long heating cycle and low heating temperature is widely used to produce sheet steels including interstitial-free (IF) steels. Optimizing batch-annealing conditions would be helpful in cutting lead time and saving energy while keeping the necessary deep drawability; however, little research has been done on it. The effects of batch-annealing parameters on the deep drawability of a Ti-stabilized IF steel and Nb+Ti-stabilized IF steel have been investigated. In general, a slight improvement in r_mvalue was found with the increase of annealing temperature. Because of the higher recrystallization temperatures of Nb+Ti-IF steel, it showed higher sensitivity to annealing temperature than Ti-IF steel. In addition, greater dependency of mechanical properties and deep drawability on soaking time was observed when annealing temperature was lower. Moreover, a heat transfer analysis showed that the annealing time could be reduced by 40% if the temperature decreases from 730°C to 650°C. The industrial production has verified that the analytical results are in good agreement with the recorded annealing temperature curve. Meanwhile, it has been shown that Ti-IF steels annealed at 650°C have very close deep drawability and other tensile properties compared with these annealed at 730°C.     

强束流钼注入铝中的反常分布研究

利用从金属蒸汽真空弧 (简称 MEVVA)离子源引出的强束流脉冲钼离子对纯铝进行了不同束流密度的离子注入试验。钼离子的加速电压为 4 8k V,剂量为 3× 10 1 7cm- 2 ,平均束流密度为 2 5和 4 7μA· cm- 2 。透射电镜 (TEM)分析证明在注入层内可形成 Al1 2 Mo晶体 ;背散射 (RBS)分析证明 Al1 2 Mo的厚度可达 6 0 0至70 0 nm;结合强束流脉冲注入的特点 ,根据碰撞理论提出了解释钼反常分布的“蜂窝”模型。     

Synthesis of N-acetyl-L-cysteine-capped ZnCdSe quantum dots via hydrothermal method and their characterization

Compared with the most studied green-red emitting (530–650 nm) quantum dots (QDs), the preparation of short-wavelength-emitting QDs remains difficult. Besides, one of the representative short-wavelength QDs materials, ZnCdSe, has a shortcoming of high content of toxic cadmium metal. In this paper, we report the synthesis of high-quality water-soluble ZnCdSe QDs via optimized one-step hydrothermal method with a new thiol as ligand, within a short time of 65 min. The emission wavelength of prepared QDs is tunable in the range of 425–540 nm by merely controlling the molar ratio of Cd:Zn or Se:Zn, and the quantum yield reaches 35%. More importantly, the maximum Cd:Zn molar ratio has been reduced to 0.04:1.0, much lower than that reported in the literature (0.5:1.0), resulting in excellent biological compatibility of prepared QDs and thus their promising applications in biological fields. Moreover, the transmission electron microscopy was employed to examine the effect of Cd:Zn ratio on the size of prepared ZnCdSe QDs, which were also characterized by x-ray photoelectron spectroscopy and electron diffraction spectroscopy.     

Reference levels at European level for cardiac interventional procedures

In interventional cardiology, a wide variation in patient dose for the same type of procedure has been recognised by different studies. Variation is almost due to procedure complexity, equipment performance, procedure protocol and operator skill. The SENTINEL consortium has performed a survey in nine european centres collecting information on near 2000 procedures, and a new set of reference levels (RLs) for coronary angiography and angioplasty and diagnostic electrophysiology has been assessed for air kerma-area product: 45, 85 and 35 Gy cm(2), effective dose: 8, 15 and 6 mSv, cumulative dose at interventional reference point: 650 and 1500 mGy, fluoroscopy time: 6.5, 15.5 and 21 min and cine frames: 700 and 1000 images, respectively. Because equipment performance and set-up are the factors contributing to patient dose variability, entrance surface air kerma for fluoroscopy, 13 mGy min(-1), and image acquisition, 0.10 mGy per frame, have also been proposed in the set of RLs.     

Creep fatigue behaviour of Type 321 stainless steel at 650°C

Abstract

Type 321 austenitic stainless steel has been used in the UK’s advanced gas cooled reactors for a wide variety of thin section components which are within the concrete pressure vessel. These components operate at typically 650°C and experience very low primary stresses. However, temperature cycling can give rise to a creep fatigue loading and the life assessment of these cycles is calculated using the R5 procedure. In order to provide materials property models and to validate creep fatigue damage predictions, the available uniaxial creep, fatigue and creep fatigue data for Type 321 have been collated and analysed. The analyses of these data have provided evolutionary models for the cyclic stress strain and the stress relaxation behaviour of Type 321 at 650°C. In addition, different methods for predicting creep fatigue damage have been compared and it has been found that the stress modified ductility exhaustion approach for calculating creep damage gave the most reliable predictions of failure in the uniaxial creep fatigue tests. Following this, validation of the new R5 methods for calculating creep and fatigue damage in weldments has been provided using the results of reversed bend fatigue and creep fatigue tests on Type 321 welded plates at 650°C in conjunction with the materials properties that were determined from the uniaxial test data.     

Hot Corrosion Behavior of Friction Welded AISI 4140 and AISI 304 in K2SO-60% NaCl Mixture

Understanding the behavior of weldment at elevated temperatures and especially the corrosion behavior has become an object of scientific investigation recently.Investigation has been carried out on friction welded AISI 4140 and AISI 304 in molten salt of K 2 SO 4-60% NaCl environment at 550,600 and 650 C under cyclic condition.The resulted oxide scales in the weldment have been characterized systematically by surface analytical techniques.From the results of the experiments,it is observed that the scale thickness on low alloy steel side was higher than that on stainless steel side.Furthermore,weld interface has been found to be more susceptible to degradation than base metals due to inter diffusion of element across the interface and the formation of intermetallic compound.The influences of welding parameters and the temperature of exposure on the hot corrosion behavior of the weldment were discussed in this paper.     

Superplasticity of Ti2448 Alloy with Nanostructured Grains

Ti-24Nb-4Zr-8Sn, abbreviated as Ti2448 from its chemical composition in weight percent, is a multifunctional β type titanium alloy with body centered cubic (bcc) crystal structure, and its highly localized plastic deformation behavior contributes significantly to grain refinement during conventional cold processing. In the paper, the nanostructured (NS) alloy with grain size less than 50 nm produced by cold rolling has been used to investigate its superplastic deformation behavior by uniaxial tensile tests at initial strain rates of 1.5×10-2, 1.5×10-3 and 1.6×10-4 s-1 and temperatures of 600, 650 and 700℃. The results show that, in comparison with the coarse-grained alloy with size of 50 μm, the NS alloy has better superplasticity with elongation up to ～275% and ultimate strength of 50–100 MPa. Strain rate sensitivity (m) of the NS alloy is 0.21, 0.30 and 0.29 for 600, 650 and 700℃, respectively. These results demonstrate that grain refinement is a valid way to enhance the superplasticity of Ti2448 alloy.     

Band-selective optical polarizer based on gold-nanowire plasmonic diffraction gratings

We report a plasmonic diffraction grating device as a new kind of optical polarizer. This simple device consists of periodically distributed gold nanowires on top of a transparent glass substrate and is based on the strong polarization dependence of the particle plasmon resonance of the gold nanowires. A high-efficiency secondary diffraction in the same device enhances the polarization extinction ratio significantly. Linearly polarized spectrum in the red with a bandwidth of 53 nm is selectively picked up from the nonpolarized white light, where a polarization extinction ratio higher than 100 at about 650 nm has been achieved. The idea of plasmonic diffraction grating is important for exploiting new detection and sensor techniques.     

A discrete element model of concrete under high triaxial loading

A numerical model based on a three dimensional Discrete Element Method (DEM) has been used to study the behavior of concrete under high-confining pressures (up to 650 MPa). At this range of pressures, irreversible compaction of the material occurs and needs to be considered. Within the discontinuous nature of the model, a local constitutive law has been developed to reproduce this phenomenon quantitatively. Local parameters to be used in this constitutive law are identified by simulating reference uniaxial and triaxial experimental tests in compression. Once these parameters have been obtained, the model is used to predict the response of concrete sample for triaxial compressive tests at different levels of confinement. Beyond the macroscopic volumetric and stress–strain response, the model gives interesting insights on the local evolution of the nature of the interaction forces between the discrete elements. The computational implementation has been carried out in the discrete element and open source code YADE (http://yade-dem.org[20]).     

多用途超低碳贝氏体钢ULCB600

试验室研制了Ｆｅ Ｃｕ Ｎｂ Ｂ系多用途的新一代超低碳贝氏体钢ＵＬＣＢ６００，并对该钢的组织结构与性能之间的关系进行了一定的分析，为工业化生产提供参考。试验钢经６５０℃时效处理后其强韧性匹配良好，力学性能达到设定要求。     

Thermopower and optical studies on undoped and manganese doped indium tin oxide films

Thermopower measurements in the range of 300-650 K along with room temperature optical absorption and electrical resistivity studies have been performed on indium tin oxide (ITO) and manganese doped indium tin oxide (Mn:ITO) thin films grown by reactive DC sputtering. The thermopower of the films measured in Ar ambient displayed irreversible changes attributable to oxygen loss. Thermopower, carrier concentration and resistivity of the films have been found to depend on oxygen vacancies and Mn concentration. The observations have been substantiated with optical absorption and room temperature electrical resistivity results. It has also been observed that band gap tuning in these films is possible by the introduction of Mn as well as oxygen vacancies.     

Work function dynamics in a Cu/W (112) adsorption system

The dynamics of work function φ in submonolayer and monolayer copper coverages of a W(112) single crystal plane has been studied at various temperatures (77, 300, and 650 K) using field emission microscopy. A model describing the formation of Cu monolayers on an anisotropic substrate is proposed.     

Structure of chemically deposited polycrystalline-silicon films

The influence of the deposition conditions on the structure of chemically deposited, polycrystalline-silicon films has been examined. The films were deposited primarily onto oxidized silicon wafers by the thermal decomposition of silane over temperature and thickness ranges of 650°–1200°C and 0.6–15 microm, respectively. After an initial induction period, which exhibits an activation energy of about 1.0 eV, island-type nucleation was observed for deposition temperatures of 850° and 1025°C; however, no islands could be resolved for a deposition temperature of 650°C. Although {110}- and {111}-texture are both important in the thinner films, {110}-texture becomes dominant over most of the temperature range as the film thickness increases. The {100}-texture is important in thicker films deposited at higher temperatures. Transmission electron microscopy indicated that the grain size increases with increasing film thickness and deposition temperature, ranging from less than 0.05 microm to more than 1 microm in the films studied. An investigation of the influence of the initial stages of deposition on the development of the texture indicated that the highly twinned {110}-grains, once nucleated, grow most rapidly. An anomalous, low-temperature structure, the effect of the reactant gas, and the influence of the substrate have been briefly investigated.     

New solution method to produce high performance thermoelectric ceramics: A case study of Bi-Sr-Co-O

Bi₂Sr₂Co_1.8O_x ceramics have been synthesized through a solution method involving the addition of polyethyleneimine as coordinating agent for the metallic cations. From these powders, bulk sintered materials have been prepared. Microstructure has been studied by means of scanning electronic microscopy (SEM) and it has shown that samples are mainly composed by the thermoelectric phase, with very small amounts of secondary phases. Electrical resistivity measurements showed very small values (around 21 mΩ cm at room temperature), nearly constant with temperature, while thermopower increases rapidly to values higher than 200 μV/K at 650 °C. Power factor value at 50 °C is about 0.08 mW/K² m and 0.20 at 650 °C, which makes this ceramic a potential material for power generation applications.