材料期刊网

Preparation of Ultrafine Si Powders from SiH_4 by Laser-induced Gas Phase Reaction

Yali LI , Yong LIANG , Kesheng XIAO , Fen ZHENG and Zhuangqi HU(State Key Laboratory of Rapidly Solidified Nonequlibrium Alloys , Institute of Metal Research , Chinese Academy of Sciences , Shenyang , 110015 , China)

材料科学技术（英文）

High quality ultrafine Si powders have been synthesized from SiH4 by laser induced gas phase reaction. The powders prduced under different synthesis conditions have mean particle size of 10-120nm in diam. with narrow particle size distribution, and free of hard agglomerates.The powders are polycrystalline with the ratio of mean grain to particle diameter being between 0.3-0.7. The size of the powder increases with increasing laser power and reaction pressure,but decreases with increasing silane gas flow rate and the addition of Ar diluent. Grain sizes drop distinctly with the rise of the addition of Ar gas and laser power, but change little with the gas flow rate and reaction temperature. The formation of Si particles under different synthesis conditions is discussed

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Preparation, Microstructure and Age Hardening of Rapidly Solidified Mo-alloys

NING Yuantao , S. H. Whang Institute of Precious Metals , Kunming , Yunnan , China. Barnett Institute of Northeastern University , Boston , MA 02115 , U. S. A.

材料科学技术（英文）

Various Mo-base alloys with high melting temperature were processed into ribbons and foils by the arc melt-spinning and the arc melt hammer-anvil technique. The preparation of ribbon and foil was introduced. The mechanical proper- ties, the surface topology and the microstructure of rapidly solidified Mo-base alloys containing B were examined. A strong grain refinement and a strong age-hardening response were observed on the as-quenched and the age specimens, the precipitates which cause age hardening were identified to be Mo_2B in Mo-B alloys, Mo_2B and ZrB_2 in Mo-Zr-B alloys, and Mo_2B and ThB_4 in Mo-Th-B alloys. The results indicate that the high strength Mo-base alloys containing boride precipitates can be developed by rapid solidifica- tion technique.

关键词: Mo-alloys , null , null , null , null

Model for calculation of microstructural development in rapidly directionally solidified immiscible alloys

Transactions of Nonferrous Metals Society of China

A model has been developed for the calculation of the microstructural evolution in a rapidly directionally solidified immiscible alloy. Numerical solutions have been performed for Al-Pb immiscible alloys. The results demonstrate that at a higher solidification velocity a constitutional supercooling region appears in front of the solid/liquid interface and the liquid-liquid decomposition takes place in this region. A higher solidification velocity leads to a higher nucleation rate and, therefore, a higher number density of the minority phase droplets. As a result, the average radius of droplets in the melt at the solid/liquid interface decreases with the solidification velocity.

关键词: immiscible alloy;directional solidification;microstructure;theory and;modeling;liquid miscibility gap

MICROSTRUCTURE AND MECHANICAL PROPERTIES OF RAPIDLY SOLIDIFIED Al-Fe BASED ALLOYS

W.J. Park , S. Ahn , R. Schmees , and Nack J. Kim(1)(Center for Advaned Aerospace Materials , POSTECH. Pohang 790-784 , Korea )2)(Research Institute of industrial Science & Technology , Pohang 790-600 , Korea )3)(Pratt and Whitney , West Palm Beach , FL , USA Manuscript received 26 August 1996)

金属学报(英文版)

The effects of additions of Ti and W on microstructure and mechanical properties of rapidly solidified Al-Fe-V-Si alloys were investigated. Alloy powders were produced by the centrifugal rotary atomization process. After atomization, powders were screened to various mesh sizes to see the effect of powder size on the mechanical properties.These Powders were consolidated into billets using conventional powder metallurgy process, and then extruded into bar form.Microstructural analysis shows that the W addition results in the heterogeneous microstructure.On the other hand, the Ti addition refines the microstructure.Alloy containing both Ti and W has the highest thermal stability of the dispersoid. These variations in the microstructure are well reflected in the mechanical properties in that the Ti containtng alloys (with or without W) have the higher strength and ductility than the W containing alloy. It also shows that the alloys made of the coarser powders have better combinations of strength and ductility than those made of the finer powders.

关键词: :rapid solidification , null , null

METASTABLE PHASES IN RAPIDLY-SOLIDIFIED ALUMINIUMRICH Al-Sm ALLOYS

Y.T.Ning (Institute of Precious Metals , Kunming 650221 , China)

金属学报(英文版)

The splat foils of Al-Sm alloys with 0.04-0.06mm in thickness were made by hammeranvil technique. The estimated cooling rute was 106K/ order of magnitude. The extended solid solubility of Sm in α-Al reached 0.5at. % Sm. The intermediate phase in the rapidlysolidified Al-Sm alloys is Al11Sm3 phase, which is stable only at temperatures above 1339K in equilibrium state and retained to ambient temperature as a metastable phase, whereas the equlibrium intermediate phase, Al3Sm, was restricted to occur.

关键词: Al-Sm alloy , null , null

MICROSTRUCTURE AND TWINNING IN ORDERED ORTHORHOMBIC MARTENSITE IN RAPIDLY SOLIDIFIED TI3AL-NB ALLOYS

Materials Letters

The microstructure of rapidly solidified Ti3Al-Nb (Nb < 5 at%) alloys prepared by the hammer-and-anvil technique consists of alpha''(0) martensite with D-2(2) (P222(1)) structure. In the martensite there are a number of twins whose twin planes are determined to be {111} by trace analysis. The twinning forms through rotation of the martensite phase (matrix) 180 degrees and it is inferred from the analysis of the martensite transition and structure of alpha''(0) martensite.

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SOME DEVELOPMENTS IN RAPIDLY SOLIDIFIED ALUMINUM ALLOYS FOR ELEVATED TEMPERATURE APPLICATIONS

P.Y. Li , S.L. Dai , C.Y. Li and B.C. Liu Beijing Institute of Aeronautical Materials , P.O.Box 81 2 , Beijing 150001 , China

金属学报(英文版)

Therecent developments in elevated temperature ( ET) aluminum alloys prepared by therapidsolidification / powder metallurgy ( RS P/ M) process were reviewed briefly. TheRS P/ METaluminum alloyscan beclassified as(a) the aluminum transition metaltype, such as Al Fe, Al Cr, Al Ti, Al Zrsystem alloys,etc.,and (b) thealuminum rareearth elementtype,such as Al Y, Al Nd system alloys,etc. Among them ,the Al Fe and Al Ti system alloysarethe most attractive, which possessthe potentialto replacethetitanium alloy partson aircraft,engines,etc.,fortheuseattemperaturesrangingfrom 200 315℃. Theproblemsin applicationsfor RS P/ M ETaluminum alloys werealso discussed .

关键词: rapidsolidification / powder metallurgy , null , null , null

Effects of Additional Elements on Microstructure and Precipitation Behaviour in Rapidly Solidified Al-Ti Base Alloys

Won-Wook Park , Chul-Jin Choi and Bong-Sun You (Dept. of Materials Processing , Korea Institute of Machinery and Metals , 66 Sangnam-Dong , Changwon , Kyungnam , Korea 641-010)(To whom correspondence should be addressed)

材料科学技术（英文）

Rapidly solidified Al-Ti base alloys were prepared by melt spinning at the cooling rate about 107 K/s. The melt-spun ribbons were used to observe the dricrostructures after heat treatment.In the supersaturated Al-Tl-Si alloy, age hardening occurred after 1 h anneal in the temperature range of 4000~500℃, which seems to be attributed to the precipitation of metastable Ll2- (Al,Si)3Ti phase. However. the microhardness was relatively low because of the low v/o and the insufflcient stability of precipitates. Thus. Cr was added to Al-Ti-Si alloys in order to stabilize the microstructures and to increase the v/o of precipitate5. As a result. the alIoys containing Cr were evaluated to possess the improved properties at the service temperature.

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Microstructure of Al-Si Alloys Rapidly Solidified from the Different Temperature Melts

Manchang GUI , Jun JIA , Guangsheng SONG , Qingchun LI

材料科学技术（英文）

Hypo- and hyper-eutectic Al-Si alloys were rapidly solidified from the low or high temperature melt using water quenching and melt-spinning technique. The differences in microstructure of rapid solidification alloys were studied by scanning and transmission electron microscopy, and X-ray diffraction methods. The primary silicon in the Al-22(wt pct)Si alloy quenched in room temperature water from high temperature melt was smaller than that quenched from low temperature melt. Compared with the ribbons spun from low temperature melt, the ribbons spun from high temperature melt had finer Al-rich and Si-rich phase particles in either Al-7(wt pct)Si or Al-18(wt pct)Si alloy. The mechanism was explained by the nature of the liquid structure.

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Microstructures and Mechanical Properties of Rapidly Solidified Mg-Al-Zn-MM Alloys

Yeon-Wook Kim

材料科学技术（英文）

Mg-Al-Zn-MM (misch metal) alloy powders were manufactured by inert gas atomization and the characteristics of alloy powders were investigated. In spite of the low fluidity and easy oxidation of the magnesium melt, the spherical powder was made successfully with the improved three piece nozzle systems of gas atomization unit. It was found that most of the solidified powders with particles size of less than 50 μm in diameter were single crystal and the solidification structure of rapidly solidified powders showed a typical dendritic morphology because of supercooling prior to nucleation. The spacing of secondary denrite arms was deceasing as the size of powders was decreasing. The rapidly solidified powders were consolidated by vacuum hot extrusion and the effects of misch metal addition to AZ91 on mechanical properties of extruded bars were also examined. During extrusion of the rapidly solidified powders, their dendritic structure was broken into fragments and remained as grains of about 3 μm in size. The Mg-Al-Ce intermetallic compounds formed in the interdendritic regions of powders were finely broken, too. The tensile strength and ductility obtained in as-extruded Mg-9 wt pct Al-1 wt pct Zn-3 wt pct MM alloy were σT.S.=383 MPa and ε=10.6%, respectively. All of these improvements on mechanical properties were resulted from the refined microstructure and second-phase dispersions.

关键词: Mg alloy , null , null , null