Effect of La2Sn2O7 content on Ag-La2Sn2O7/SnO2 arc erosion behavior and mechanism

La₂Sn₂O₇/SnO₂ powder was synthesized by chemical co-precipitation method, and Ag-La₂Sn₂O₇/SnO₂ composites were prepared by hot-pressing sintering. The electrical resistivity, density, Brinell hardness and flexural strength of Ag-La₂Sn₂O₇/SnO₂ composites were measured. Moreover, the effect of La₂Sn₂O₇ content on the arc erosion behavior of Ag-La₂Sn₂O₇/SnO₂ composites at 7 kV voltage was studied. With the increase of La₂Sn₂O₇ content, the arc duration and arc energy decrease, and the breakdown strength increases. The surface morphology of Ag-La₂Sn₂O₇/SnO₂ composites after arc erosion was investigated using scanning electron microscopy and three-dimensional laser confocal scanning microscopy. With the increase of La₂Sn₂O₇ content, the smaller the erosion damage, the better the anti-arc erosion performance. However, too much La₂Sn₂O₇ results in the decrease of Ag-La₂Sn₂O₇/SnO₂ properties and severe arc erosion. X-ray photoelectron spectroscopy was used to determine the composition of the erosion region. The effect of La₂Sn₂O₇ on wettability between Ag and SnO₂ was investigated, and the erosion mechanism of Ag-La₂Sn₂O₇/SnO₂ composites was discussed systematically. This study can provide a reference for the application of Ag matrix electrical contact materials in high-voltage electrical appliances.     

Crystal multiplication in undercooled Cu + 2 Pct Sn alloy

The effects of undercooling (AT) from 10 to 175° on grain structure were observed in a Cu + 2 wt pct Sn alloy, in which grain refinement does not occur at large degrees of under-cooling. Quenching soon after recalescence retained transient grain structures not previ-ously reported in the literature. Crystal multiplication by dendrite fragmentation occur-red when undercooling below the liquidus lay in the range △T = 10 to 70°, and resulted in complete grain refinement in the range △T = 50 to 70°. Fragmentation affected primary, secondary and tertiary dendrite arms during and after recalescence. At △T = 70° a sharp transition occurred to a radiating fan-shaped structure of twin-related grains ori-ginating from a single point of nucleation, with no evidence of fragmentation. It is pro-posed that the transition results from a change in the free dendritic growth mode, the new shape being a wholly primary form without side-arms. The absence of fragmentation in this range (△T > 70°) suggests that self-buckling contributes to fragmentation in the other range (△T < 70°) and could be at least equal in importance to remelting. Formerly with the University of Queensland, Australia, and the National Research Council of Canada, Ottawa     

含锡C--Mn钢中锡的析出相

利用扫描电镜/能谱仪和透射电镜表征了残余元素Sn在C-Mn钢中的存在形式,同时考察了热处理温度对含Sn析出相类型的影响.结果表明:Fe-5% Sn中Sn以第二相形式在晶界与晶内析出;Fe-1.5% Sn-0.2% S中Sn以第二相形式在直径2~4 μm的球形MnS夹杂物上异质析出.透射电镜分析和热处理实验结果表明:在Fe-5% Sn及Fe-1.5% Sn-0.2% S中MnS夹杂上析出的含Sn第二相结构为四方晶系的FeSn₂相.      

Hydrogen-induced slow crack growth in Ti-6Al-6V-2Sn

The effect of hydrogen and temperature on threshold stress intensity and crack growth kinetics was studied in Ti-6Al-6V-2Sn containing 38 ppm hydrogen. A slight decrease in threshold values occurred as temperature decreased from 300 K while they increased significantly above 300 K. For a given test temperature, crack growth rates exhibited an exponential dependence on stress intensity over a major portion of growth. At 300 K the rates reached a maximum. Slow crack growth occurred predominately by cleavage ofα grains which has been associated with hydride formation. The stress intensity required for hydride formation at a crack tip can be determined from hydrogen concentration and solubility considerations under stress. As these values differed from observed thresholds, a strong influence of microstructure was suggested and subsequently revealed by crack front examination. Quantification of this effect with a modified Dugdale-Barenblatt model relates the effective stress intensity at the crack tip to the applied stress intensity. Microstructure was also found to exert a strong influence on slow crack growth behavior when examined in terms of the effective stress intensity,K _eff. From Arrhenius plots of crack growth rates for variousK _eff, activation energies of 27.0 to 32.8 kJ/mol were obtained and related to the diffusion of hydrogen through theβ phase. The increase in crack growth rates with increasing temperatures up to 300 K is attributed to the temperature dependence of hydrogen diffusion. The decrease in crack growth rates above 300 K is related to a hydride nucleation problem.     

Tb~(3+)掺杂Gd_2Sn_2O_7纳米荧光材料的制备与光学性能

采用共沉淀-水热法合成Tb3+掺杂Gd2Sn2O7纳米荧光材料,并采用X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)、傅里叶变换红外光谱(FT-IR)、拉曼光谱(Raman)和荧光光谱对合成产物的晶体结构、颗粒尺寸、形貌和光学性能进行研究。研究结果表明水热合成产物为单一相立方烧绿石结构Gd2Sn2O7:Tb3+晶体,产物由尺寸约为50~70 nm的一次纳米颗粒团聚而成的不规则球。激发光谱和发射光谱测试结果表明,Gd2Sn2O7:Tb3+样品可以被379 nm的紫外光有效地激发而发射出纯度高的Tb3+离子特征的绿光,在高浓度Tb3+掺杂时可观察到Tb3+发光浓度猝灭现象。在样品的激发光谱中观察到不同激发带的猝灭浓度并不相同,并对其原因进行了分析。     

Effect of Substrate Composition on Sn Whisker Growth in Pure Sn Films

Pure Sn films deposited on Cu and Cu alloys are prone to spontaneous whisker formation. One way of preventing whisker formation is to alloy Pb into Sn coatings. However, restriction on the use of Pb demands the development of alternative methods for preventing whisker growth. The present work reports the effect of substrate composition on whisker formation and morphology. Despite employing identical plating conditions, long filament-like whiskers grew only on Sn-plated Cu samples and not on brass. The presence or lack of Sn whiskers has been explained via the thermodynamic stability of various intermetallic compounds at the Sn/substrate interface.     

Effect of Sn on the Dehydrogenation Process of TiH2 in Al Foams

The study of the dehydrogenation process of TiH₂ in aluminum foams produced by the powder metallurgy technique is essential to understanding its foaming behavior. Tin was added to the Al foam to modify the dehydrogenation process and stabilize the foam. A gradual decomposition and more retention of hydrogen gas can be achieved with Sn addition resulting in a gradual and larger expansion of the foam.     

Subcritical crack-growth under sustained load in Ti-6AI-6V-2Sn

The subcritical sustained-load cracking (SLC) behavior of beta annealed, recrystallization annealed, and solution-treat-and-aged Ti-6Al-6V-2Sn was studied in dry argon and moist air. The effects of microstructure, internal hydrogen concentration, specimen orientation, and specimen thickness on threshold stress-intensity and crack-growth rate were determined under increasing stress-intensity conditions using wedge-opening load (WOL) specimens, and the fracture morphologies were studied by scanning electron microscopy. The SLC threshold stress intensities are lower and crack growth rates are higher in solution-treatand-aged condition than in beta-annealed and recrystallization conditions. The plane strain conditions increase the susceptibility to SLC. The texture effects on SLC are intensified when the cracking plane is close to the basal plane. For low interstitial-hydrogen concentrations ≈10 ppm, sustained-load crack growth is controlled by creep at the crack tip. Increased hydrogen concentration results in enhanced cleavage, lower threshold stress-intensity, and accelerated crack-growth. Of the possible mechanisms for hydrogen-assisted SLC in Ti-6Al-6V-2Sn, the most likely is that involving preferential segregation of hydrogen to beta phase, leading to fracture by α-β interface separation. Formerly with McDonnell Douglas Research Laboratories.     

Ag3Sn Morphology Transitions During Eutectic Growth in Sn–Ag Alloys

Metallurgical and Materials Transactions A - Eutectic Ag3Sn can grow with a variety of morphologies depending on the solidification conditions and plays an important role in the performance of...