材料期刊网

SOLIDIFICATION MECHANISM OF UNDERCOOLED SINGLE PHASE ALLOYS

J.F. Li , G.C. Yang and Y.H. Zhou(State Key Laboratory of Solidification Processing , Northwestern Polytechnical University , Xi'an 710072 , China)

金属学报(英文版)

The solidification behavior of bulk undercooled Ni50Cu50 alloy was systematically investigated. Double recalescences were discovered for the first time in a single phase Ni-Cd alloy, in which there is no solid phase transition at elevated temperature. When the alloy melt was undercoolcd below the solidus temperature, the effect of nonequilibrium solidification could make the solid with the norminal composition C0 of the alloy nucleate and grow till tempemture approached To (the temperuture at which the free enengies of solid and liquid with C0 are equal). Following it, the nucleation and growth of the solid with more high melting point component were required, so the secondary recalescence took place. The concentration distribution in crystals was also analysed.

关键词: undercooled Ni-Cu alloy , null , null

GRAIN REFINEMENT IN BULK HYPERCOOLED Ni_(50)Cu_(50) ALLOY

G.S. Song , Z.Z. Zhang , X.B. Dong , G.C. Yang and Y.H. Zhou(State Key Laboratory of Solidification Processing , Northwestern Polytechnical University , Xi'an 710072 , China)

金属学报(英文版)

Undereooling eoperiments on binary Ni50 Cu50 alloy melts were conducted. The hypercooling limit of this alloy, which is about 310K, was evaluated by mcasuring plateau time needed for the interkendritic liquid solidification and extmpolating this function to zero. This limit was exceeded first in the binary alloy undereooled by about 320K.The effect of liquid undercooling on the respective microstructure evolution was studied by optical metallogrnphy. The hypercooled microstructure contains rcsidual fragments within grain boundaries and is quite different from those obtained at undercoolings below 310K. The finding indicated the existence of dendrite break up. The dendrite break up may be induced either by remelting or by stress. By considering hyperrooling conditions and comparing two grain ndnement microstructures observed at small and larpe undereoolings, the forms of dendrite break up and the grain refinement mechanism exceeding the hypereooling limit are further discussed.

关键词: hypercooling , null , null , null

The g factors of ground state of ruby and their pressure-induced shifts

Communications in Theoretical Physics

By using the theory of pressure-induced shifts and the eigenfunctions at normal and various pressures obtained from the diagonalization of the complete d(3) energy matrix adopting C-3v symmetry, g factors of the ground state of ruby and their pressure-induced shifts have been calculated. The results are in very good agreement with the experimental data. For the precise calculation of properties of the ground state, it is necessary to take into account the effects of all the excited states by the diagonalization of the complete energy matrix.

关键词: crystal fields;g factors;ruby;high-pressure effects

Microstructural evolution in AISI 304 stainless steel during directional solidification and subsequent solid-state transformation

Materials Science and Engineering a-Structural Materials Properties Microstructure and Processing

The microstructural evolution during solidification and subsequent solid-state transformation of AISI 304 stainless steel is studied by directional solidification and quenching methods in this paper. The phase transformation sequence in the steel directionally solidified is that the precipitation of primary ferritic dendrites, ferrite-austenite eutectic reaction, and the direct formation of austenite occur in sequence during the directional solidification of the austenitic stainless steel. At the eutectic reaction stage, plenty of columnar and cellular eutectic colonies composed of the coupled growth of lamellar ferrite and austenite take place. During the course of subsequent solid-state transformation, austenite grows into ferrite gradually, resulting in the disappearing of eutectic colonies and thinning of primary ferritic dendrites, and dendrite cores of primary ferrite are retained as the final skeletal ferrite in the final microstructure. (c) 2006 Elsevier B.V. All rights reserved.

关键词: austenitic stainless steel;directional solidification;eutectic colony;austenitic stainless-steel;cr-ni alloys;sequence;welds

Correlation between the surface state and optical properties of S(6) site and C(2) site in nanocrystalline Eu(3+):Y(2)O(3)

Journal of Alloys and Compounds

Eu(3+) doped Y(2)O(3) nanocrystals are synthesized via precipitation and hydrothermal methods. With the increase of hydrothermal temperature, the number of surface states decreases when nanorods are formed. The decrease of surface states induces the increase in the ratio of S(6) site to C(2) site, and meanwhile results in the spectral red-shift of charge transfer band as well as the enhancement of red emission. The results indicate that the surface states and optical properties have close correlations. (C) 2010 Elsevier By. All rights reserved.

关键词: Luminescence;Hydrothermal method;Nanocrystals;Optical properties;luminescence properties;hydrothermal synthesis;size;eu3+;y2o3;photoluminescence;nanopowders;symmetry;ceramics;phosphor

Solidification pathways and constituent phases of Mg-Zn-Y-Zr alloys

Journal of Alloys and Compounds

Thermal analysis with cooling curve has been used for investigation of microstructure evolution with composition variation during solidification process in Mg-Zn-Y-Zr alloys (denoted as ZW alloys). The obtained results reveal that two pseudobinary eutectic reactions appear one after another during solidification due to the different Zn/Y ratio (ranged front 0.35 to 3.33). In ZW62 alloy, a peritectic reaction happens before I-phase Formation through pseudobinary eutectic reaction distinguishing it from other alloys. The changes of characteristic temperature points for phase transformation are studied in detail. Microstructure observation shows dominating secondary phases in the alloys differ from one another according to various Zn/Y ratios. Divorced massive eutectic Z-phase is formed during solidification in a low Zn/Y ratio: W-phase comes out when Zn/Y ratio grows to 0.85; if the Zn/Y ratio increases further to a certain level, I-phase forms by a peritectic reaction through W-phase and the liquid. (C) 2008 Elsevier B.V. All rights reserved.

关键词: Thermal analysis;Mg-Zn-Y-Zr alloy;Solidification pathway;Phase;constituent;mechanical-properties;system;microstructure;magnesium

g-C(3)N(4) coated SrTiO(3) as an efficient photocatalyst for H(2) production in aqueous solution under visible light irradiation

International Journal of Hydrogen Energy

A highly active photocatalyst based on g-C(3)N(4) coated SrTiO(3) has been synthesized simply by decomposing urea in the presence of SrTiO(3) at 400 degrees C. The catalyst demonstrates a high H(2) production rate similar to 440 mu mol h(-1)/g catalyst in aqueous solution under visible light irradiation, which is much higher than conventional anion doped SrTiO(3) or physical mixtures of g-C(3)N(4) and SrTiO(3). The improved photocatalytic activity can be ascribed to the close interfacial connections between g-C(3)N(4) and SrTiO(3) where photo-generated electron and holes are effectively separated. The newly synthesized catalyst also exhibited a stable performance in the repeated experiments. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

关键词: Carbon nitride;Photocatalyst;Visible light;SrTiO(3);tio2 nanotube photocatalyst;hydrogen-production;water;generation;oxynitride

Corrosion of Y, Fe and Fe-15Y in H-2-H2S mixture under 10(-3) Pa S-2 at 600 similar to 800 degrees C

材料科学技术（英文）

The corrosion of an Fe-based alloy containing 15 wt pet Y in H-2-H2S mixtures under 10(-3) Pa S-2 was studied at 600 similar to 800 degrees C in an attempt to find materials with improved sulphidation resistance with respect to pure Fe. The presence of Y has been shown to be beneficial, but not sufficient to the level expected. In fact, the alloy is able to form at all tested temperatures an external FeS layer, beneath which a zone containing a mixture of the two sulphides is also present. Thus, Fe can still diffuse through this region to form the outer FeS layer with non-negligible rate. The corrosion rate of Fe is considerably reduced by the Y addition, but the alloy corrodes still much more rapidly than Y. The sulphidation kinetics is generally rather irregular for both the pure metals, while the corrosion rate of the alloy decreases with time and tends to become parabolic after an initial period of 12 similar to 17 h. The sulphidation behaviour of the alloys is discussed by taking into account the presence of an intermetallic compound Fe17Y2 and the limited solubility of Y in Fe.

关键词: high-temperature sulfidation;most-reactive component;ni-nb alloys;h2-h2s mixtures;behavior;600-degrees-c-800-degrees-c;oxidation

Inversion Solidification Cladding of H90Steel

LI Baomian , XU Guangming , CUI Jianzhong

钢铁研究学报(英文版)

The variation law of cladding thickness as well as the structures and properties of H90steel clad strip produced by inversion solidification was studied. The interface bonding mechanisms were approached. It is found that the thickness of H90 cladding goes sequentially through the solidification growth stage, holding stage, and remelting stage, with an increase in immersion time. The higher the preheating temperature of the steel coil, the thicker is the maximum cladding thickness. Observation by using optical microscopy (OM) and the electron probe microanalyzer (EPMA) shows that the microstructure of H90 cladding is composed of equiaxed grains, and that interdiffusion between Cu and Fe at interface occurs but obvious diffusion of Zn and the intermetallic layer are not observed. The diffusion layer is thin and about 4 μm. Multipass small reduction cold rolling and repeated bending tests show that the interface is firmly bonded. Tensile test shows that the mechanical properties of the asclad strips can meet the requirements of GB52132001 for the Fgrade deepdrawing steel plate though there is a slight difference in the mechanical properties among the clad strips with different cladding thickness.

关键词: inversion solidification;clad coil;clad layer;interface;bond strength

Laboratory of Solid State Microstructures(LSSMS)

材料科学技术（英文）

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