LI Jianguo MAO Xiemin FU Hengzhi National Laboratory of solidification Technology
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Northwestern Polytechnical University
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Xi'an
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China Lecturer.Faculty No.403
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Northwestern Polytechnical University
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Xi'an 710072
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China
金属学报(英文版)
The interface morphologies and microstruetures of the directionally solidified Ni-5wt-% Cu alloy during dendrite-to-cell transition at high growth rates have been investigated with a newly developed apparatus for unidirectional solidification with the temperature gradient at the solid/liquid interface higher than 1000 K/cm.The results show that in the vicinity of dendrite-to-cell transition point,the well developed sidebranches become shrivelled with the increase of growth rate and disappear at the dendrite-to-cell transition,and the primary spacing decreases simultaneously.Moreover,the length of mushy zone decreases greatly dur- ing the dendrite-to-cell transition.Cells obtained at high growth rates have very similar morphologies to those at low growth rates,but with much smaller cell spacings and unsmoothed cell walls which may be attributed to the different stability conditions of the cell walls at low and high growth rates respectively.
关键词:
cellular growth
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null
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null
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Metallurgical Transactions B-Process Metallurgy
In this work, the solidification and segregation behaviors of 8090 Al-Li alloy have been investigated with differential thermal analysis (DTA) and the metallographic-electron microprobe method. The results show that 8090 Al-Li alloy has a much more complex solidification path than Al-Li binary alloy due to the addition of many alloying elements and the presence of impure elements. Solidification begins at about 635-degrees-C with the reaction of L --> alpha-Al + L', and this reaction goes on to termination. The alloying element Cu and impure elements Fe and Si have a strong segregation tendency. During solidification, Cu segregates to the interdendrite and finally forms alpha-Al + T2 eutectic. As a result, the solidification temperature range is greatly extended. Iron and Si form the insoluble constituents Al7Cu2Fe, AlLiSi, etc., although their concentrations in the alloy are quite low. With the increase of Fe content, there is a eutectic reaction of alpha-Al/Al3Fe at about 595-degrees-C. The formation of insoluble constituents is influenced by both concentrations of impure elements in the alloy and the cooling rate.
关键词:
fracture-behavior;phase-equilibria;cu alloys;microstructure;lithium;zr
Materials and Corrosion-Werkstoffe Und Korrosion
Micro-arc oxidation (MAO) has been accomplished on Mg-Li alloy in alkaline polyphosphate electrolytes without and with the addition of 10?g/L?K2TiF6. The surface/cross-section microstructures of the fabricated coatings were analyzed by scanning electron microscope (SEM); the compositions of the fabricated MAO coatings were analyzed by X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDAX); the corrosion behaviors of bare and MAO coated Mg-Li alloys were evaluated using potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) in 3.5?wt% NaCl solution. Novel hybrid MAO coatings which showed hybrid composition of MgF2/Ti2O5/Ti6O11/MgO, as well as hybrid structure of a dense inner layer, a dense outer layer and an intermediate layer with some sealed/semi-sealed pores, had been fabricated on Mg-Li alloy in alkaline polyphosphate electrolytes with the addition of K2TiF6. Meanwhile, the corrosion resistance of the fabricated MAO coatings was improved obviously as the result of the addition of K2TiF6 in the electrolytes. Moreover, the multiple roles of ${\rm TiF}_{{\rm 6}}boolean AND{{\rm 2}{-} } $ on the MAO process accounted for the fabrication of the corrosion-resistant hybrid MAO coatings.
关键词:
corrosion resistance;Mg-Li alloy;micro-arc oxidation;az91d magnesium alloy;corrosion-resistance;phosphate electrolytes;ceramic coatings;zn alloy;silicate;performance;aluminum;behavior
WADSWORTH Jeffrey and FLUSS Michael(Chemistry and Materials Science Directorate
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Lawrence Livermore National Laboratory
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Livermore
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CA 94551)
金属学报(英文版)
The role of the National Laboratories is summarized from the era of post World War II to the present time. The U.S. federal government policy for the National Laboratories and its influence on their materials science infrastructure is reviewed with respect to .determining overall research strategies, various initiatives to interact with industry (especially in recent years),building facilities that serve the nation, and developing leading edge research in the materials sciences. Despite reductions in support for research in the U.S. in recent years, and uncertainties regarding the specific policies for Research &Development (R&D) in the U.S., there are strong roles for materials research at the National Laboratories. These roles will be centered on the abilities of the National Laboratories to field multidisciplinary teams, the use of unique cutting edge facilities, a focus on areas of strength within each of the labs,increased teaming and partnerships, and the selection of motivated research areas. It is hoped that such teaming opportunities will include new alliances with China, in a manner similar, perhaps, to those recently achieved between the U.S. and other countries.
关键词:
: U.S. Materials Science. U.S. National Laboratories and Facilities
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null
LIU Yulin ZHANG Yun ZHAO Hong'en HU Zhuangqi SHI Changxu Institute of Metal Research
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Academia Sinica
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Shenyang
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China Associate Professor
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Institute of Metal Research
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Academia Sinica
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Shenyang 110015
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China
金属学报(英文版)
The solid-liquid interface morphology and solute segregation behaviour of AI-Li alloy 8090 during unidirectional solidification were studied by the liquid metal quenehing method under varied processing conditions.When solidification rate,RO.75 mm/min (temper- ature gradient,G_L=130℃/cm),the structure revealed of planar or dendritic interface respectively.With the increase of R,the interface morphology becomes cellular from planar gradually,within a narrow range.And the greater the R,the,finer the dendrite.Segregation of element Cu and impurity elements Fe and Si are quite severe,the interface morphology markedly influences on solute segregation.During solidification at coarse dendrite interface, their segregation ratios are rather great and solidified structure is coarse.
关键词:
Al-Li alloy
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null
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null
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null
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万小峰
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张久兴
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周文元
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李湘波
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周美玲
稀有金属材料与工程
研究了FU105大功率广播发射管用碳化镧钼阴极,参照碳化钍钨阴极FU105管的制备工艺,实现了镧钼阴极的碳化以及镧钼阴极FU105管的排气和老炼.通过镧钼阴极FU105管的性能测试,对碳化镧钼阴极的发射能力和稳定性进行了分析.结果认为:FU105管碳化镧钼阴极的发射能力可以达到碳化钍钨阴极的水平,但其稳定性还有待改进.
关键词:
镧钼阴极
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FU105发射管
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碳化
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稀土
Materials and Corrosion-Werkstoffe Und Korrosion
A rapid and convenient anodization technology with AC power source to obtain the MAO films formed on magnesium alloy AZ91D in phosphate bath (base electrolyte + Na3PO4) with or without aluminate and silicate was studied. The corrosion resistance of the anodic films was studied by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques and the microstructure and composition of films were examined by SEM and XRD. The results show that Na3PO4 can promote the occurrence of sparking during the MAO process, while abundant heat generated by sparking might enhance the formation of the glassy phase of the compound when the electrolyte contains the additives of NaAlO2 and Na2SiO3 simultaneously. The optimized MAO film is ivory-white smooth by naked eye, while presents porous and microcracks in microscopic scale. The anodic film formed in the alkaline solution with optimized parameters possesses superior corrosion resistance by electrochemical test. The XRD pattern shows that the components of the anodized film consist of MgO, MgAlO2, and MgSiO3. No oxide crystal with P element can be found.
关键词:
micro-arc oxidation;electrochemical impedance spectroscopy;koh-aluminate solutions;corrosion protection;ceramic coatings;alloys;anodization;parameters;resistance;behavior
Corrosion Science
The early stages of the evolution of atmospheric corrosion of carbon steels exposed in both a laboratory simulated and a natural atmosphere environment in Shenyang have been observed by in situ scanning electron microscopy. In the case of laboratory cyclic wet-dry tests, even though the chloride content level is very low, filiform corrosion is initiated in the early stage. The filiform corrosion grows in random directions, forming a network of ridges. White nodules nucleate and grow on the ridges during continued corrosion and eventually connect with each other to form the initial corrosion scale. Pits were also found on the surface beneath corrosion products. In the case of a natural atmospheric environment, both filiform corrosion and other localized corrosion, such as pitting and inter-granular attack take place in the initial stage. It is obvious that there is variety of localized corrosion in the initial stage of atmospheric corrosion. (C) 2007 Elsevier Ltd. All rights reserved.
关键词:
steel;atmospheric corrosion;initial stage;localized corrosion;in-situ;iron;electrolyte;thickness
G.Montay
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A.Cherouat
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A.Nussair
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J.Lu
材料科学技术（英）
Residual stress in coatings is the result of individual particle stress. Their effects may be either beneficial or detrimental, depending upon the magnitude, sign and distribution of the stresses with respect to the external load. Tensile stress which exceeds the elastic limit causes cracking in surface coatings or at the interface between the substrate and the coat. Compressive stress, in general, has a beneficial effect on the fatigue life, crack propagation, coating adhesion and on the durability of the top coat during service. Compressive residual stresses can increase the number of cycles before crack initiation begins through a mean stress effect. Temperature gradients which occur during solidification and subsequent cooling are the principal mode of internal stresses generation. Some parameters influence the residual stress field of both the coating and the substrate. Substrate nature, spraying temperature, thickness of the coat layer, substrate preparation (grit blasting conditions), and velocity of the splats are in the relation with the quality of the coating. In this work, we will describe the role playing by the ceramics coating elaboration on the residual stress gradient in depth of the component. The incremental hole drilling technique has been developed to determine the residual stress gradient in depth of the coat and substrate which must be used with particularly conditions. This new technology has been employed on zirconia, alumina and tungsten carbide plasma sprayed coating.
关键词:
Coating
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null
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null
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