Improving austenitic stainless steel resistance spot weld quality using external magnetic field

A ring-shaped permanent magnet is applied in resistance spot welding to improve the weld quality of austenitic stainless steel. Under the action of an external magnetic field, the profile of the weld nugget became peanut-shaped instead of ellipsoidal. The crystal orientation near the faying surface was less directional, and equiaxed grains were formed in weld nugget centre. Moreover, the shrinkage cavities tendency in traditional resistance spot welds was reduced. The relatively slow cooling speed could cause element segregation and thus change solidification mode and significantly affect weld microstructures. The mechanical performance of the welds was finally improved by the applied external magnetic field in terms of microhardness and lap-shear strength.     

高铌TiAl合金钎焊接头组织和性能研究

采用Ti-28Ni(wt.%)共晶钎料在1100℃实现了高铌TiAl合金(Ti-45Al-8.5Nb-(W, B, Y) (at.%), 简称TAN)的真空钎焊连接。钎焊接头的典型界面结构为TAN/τ3-Al3Ti2Ni + B2/α2-Ti3Al layer/α2-Ti3Al + δ-Ti2Ni/α2-Ti3Al layer/τ3-Al3Ti2Ni + B2/TAN。深入研究了保温时间对钎焊接头界面组织和连接性能的影响。结果表明：Ni元素从熔融钎料向TAN母材的扩散决定了界面组织的演化,随着保温时间的延长促进了扩散层的增厚,同时导致钎缝宽度逐渐减小。接头剪切强度测试结果显示当保温时间为15分钟时,获得的最大接头室温剪切强度和高温(600℃)剪切强度分别是248.6MPa和166.4MPa。接头断口分析表明在剪切实验中裂纹主要沿着连续的金属间化合物层产生和扩展。     

Phase Equilibria in the Cu-Sn-Sb Ternary System

The phase equilibria in the Cu-Sn-Sb ternary system were investigated by means of electron-probe microanalysis and x-ray diffraction. Firstly, ternary solubilities of η-Cu₆Sn₅, δ-Cu₄₁Sn₁₁, Cu₁₁Sb₃, ε-Cu₃Sb and η-Cu₂Sb, were less than 7 at.% Sb or Sn at 400 °C. Besides, an re-stabilized ternary solubility, Cu₆(Sn,Sb)₅, was detected with a homogeneity range of Cu: 52.9-53.3 at.%, Sn: 28.4-30.9 at.%, and Sb: 15.8-18.7 at.%. Its origin was traced back to high-temperature stabilization of the binary η-Cu₆Sn₅ phase. Thirdly, the metastable phase, Cu₁₁Sb₃, was observed at 400 °C in the Cu-Sn-Sb ternary system; On raising the temperature to 500 °C, the ε-Cu₃Sn phase still retained a large solubility for Sb, at?~?16 at.%, while the ε-Cu₃Sb was replaced by β-Cu₃Sb with a dual-cornered large homogeneity range. Similarly, a ternary homogeneity range of Cu: 83.8-84.9 at.%, Sn: 2.6-6.2 at.%, and Sb: 9-12.5 at.%, was found and deduced to be the high temperature stabilization phase of γ-Cu₁₁(Sb,Sn)₂ at 500 °C.     

Comparison Study on Additive Manufacturing (AM) and Powder Metallurgy (PM) AlSi10Mg Alloys

The microstructural and mechanical properties of AlSi10Mg alloys fabricated by additive manufacturing (AM) and powder metallurgy (PM) routes were investigated and compared. The microstructures were examined by scanning electron microscopy assisted with electron-dispersive spectroscopy. The crystalline features were studied by x-ray diffraction and electron backscatter diffraction. Room-temperature tensile tests and Vickers hardness measurements were performed to characterize the mechanical properties. It was found that the AM alloy had coarser Al grains but much finer Si precipitates compared with the PM alloy. Consequently, the AM alloy showed more than 100% increment in strength and hardness compared with the PM alloy due to the presence of ultrafine forms of Si, while exhibiting moderate ductility.     

Growth of Inclined GaAs Nanowires by Molecular Beam Epitaxy: Theory and Experiment

The growth of inclined GaAs nanowires (NWs) during molecular beam epitaxy (MBE) on the rotating substrates is studied. The growth model provides explicitly the NW length as a function of radius, supersaturations, diffusion lengths and the tilt angle. Growth experiments are carried out on the GaAs(211)A and GaAs(111)B substrates. It is found that 20° inclined NWs are two times longer in average, which is explained by a larger impingement rate on their sidewalls. We find that the effective diffusion length at 550°C amounts to 12 nm for the surface adatoms and is more than 5,000 nm for the sidewall adatoms. Supersaturations of surface and sidewall adatoms are also estimated. The obtained results show the importance of sidewall adatoms in the MBE growth of NWs, neglected in a number of earlier studies.     

High frequency mass transfer responses with polyaniline modified electrodes by using new ac-electrogravimetry device

For many years, polyaniline films have appeared to be one of the most studied conducting polymers. At the same time, ac-electrogravimetry has been used as a powerful technique for different polymer films but in general for slow perturbation rates. Two reasons for that: on the one hand, high frequency mass transfer responses are not expected and on the other hand, the electronic interfaces dedicated for ac-electrogravimetry are not prepared to follow, without distortion, high rate frequency shifts, faster than a few hertz. This paper shows that high ionic transfer responses can be detected by using a new ac-electrogravimetry concept. The experiments conducted with PANI tried to verify whether high frequency responses in conducting polymers are possible or not. The main interest of the new device is to reach the high frequency values directly and to demonstrate an ionic transfer contribution at 1 kHz which was not predicted with old systems.     

Chemical model for cement-based materials: Thermodynamic data assessment for phases other than C-S-H

In the context of waste confinement, concrete may be used both as a confinement and as a building material. Concerning radwaste, the heat released during radioactive decay will modify the equilibrium constants of the minerals forming the concrete. The present work aims to elucidate the temperature dependency of the thermodynamic functions related to minerals from the concrete or associated with some of its degradation products. A large set of experimental data has been collected, for the chemical systems SO₃-Al₂O₃-CaO-CO₂-Cl-H₂O and SiO₂-Al₂O₃-CaO-H₂O, including iron and magnesium bearing phases. Most of the data collected concern experiments in aqueous media but results from calorimetric studies were also included, when available. Based on selected thermodynamic properties for each phase, predominance diagrams were drawn for the chemical elements listed above. Phase relations reported into predominance diagram appear rather consistent with most of the literature results. The case of katoite has been especially discussed, because it shows inconsistencies with respect to a hydrogarnet-grossular solid solution and with respect to phase relations reported into already published works. Finally, we underline the chemical compatibility of Portland cement pastes with carbonate aggregates, compared to silicates, for long-term storage applications.     

Identification and evaluation of modification level for compacted graphite cast iron

The shape of the freezing zone of a thermal analysis cooling curve not only contains the information about the modification level of compacted graphite cast iron (CGI) right after vermicularizing treatment, but also reflects the following fading process during holding. When the freezing zones of two cooling curves are approximately the same, graphite morphologies of the samples cast from the two corresponding melts right after vermicularizing treatment are similar, and those of the two corresponding samples cast after holding for the same period are similar too. Based on the pattern recognition method and database established from a large amount of experimental results, the shape of the freezing zone of a cooling curve can be used to identify the modification level of CGI melt and on-line prediction of a CGI melt quality has been realized.     

Synthesis and electrochemical properties of monoclinic Li3V2(PO4)3/C composite cathode material prepared from a sucrose-containing precursor

Monoclinic structure Li₃V₂(PO₄)₃/C composite powders are synthesized via a novel homogeneous mixing route followed by a one-step heat treatment. The composites were characterized by X-ray diffraction (XRD) and galvanostatic charge/discharge, CV measurements. The influence of the heat treatment on the electrochemical properties of Li₃V₂(PO₄)₃/C composites was investigated. To examine the effect of residual carbon content on the properties of the composites, six samples with 1.2, 2.3, 3.4, 4.4, 5.8, and 7.0 wt% carbon were prepared. The sample with 4.4 wt% carbon exhibited good cycling performance and rate capability in the range of 3.0–4.8 V.     

A Simple Method to Synthesize Cadmium Hydroxide Nanobelts

Cd(OH)₂ nanobelts have been synthesized in high yield by a convenient polyol method for the first time. XRD, XPS, FESEM, and TEM were used to characterize the product, which revealed that the product consisted of belt-like crystals about 40 nm in thickness and length up to several hundreds of micrometers. Studies found that the viscosity of the solvent has important influence on the morphology of the final products. The optical absorption spectrum indicates that the Cd(OH)₂ nanobelts have a direct band gap of 4.45 eV.