材料期刊网

CREEP PROPERTIES OF HIGH SILICON ALLOY ZA27 PREPARED BY SPRAY DEPOSITION

YANG Liushuan , LIU Yongchang , YANG Gencang , ZHOU Yaohe(State Key Laboratory of Solidification Processing , Northwestern Polytechnic University , Xi'an , 710072 , China)

金属学报(英文版)

The elevated temperature creep properties(90-150℃) of high silicon(～6wt%Si) alloy ZA27 prepared by spray deposition have been investigated by means of ball hardness testing method.The results indicate that the creep properties of the material prepared by spray deposition are notably improved,compared to that of the conventional casting alloy ZA27.The creep activation energy of the spray deposited alloy ZA27 is 3.9-5.7 kJ/mol higher than that of the conventional casting alloy ZA27.The creep formulation in this experiment is also derived as follows:HB-2-HB0-2=K exp(- Q/3RT)(t1/3-t01/3)The reasons for the improvement of creep resistance are also discussed from a microstructural point of view.

关键词: :spray deposition , null , null , null

Laboratory of Solid State Microstructures(LSSMS)

材料科学技术（英文）

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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

Competitive Nucleation and Rapid Growth of Co-Si Intermetallic Compounds during Eutectic Solidification under Containerless Processing Conditionion

Wenjing Yao

材料科学技术（英文）

The liquid-solid transitions of (Co₂Si+CoSi) and (CoSi+CoSi₂) eutectic alloys were realized in drop tube and the rapid eutectic growth mechanism of intermetallic compounds was examined. The experimental and calculated results indicate that with increasing Co content, the intermetallic compound prefers nucleating primarily. The eutectic microstructures experience the transitions of `lamellar-anomalous-divorced' eutectic with undercooling. In undercooled state, the growth of CoSi intermetallic compound always lags behind others, and no matter how large the undercooling is, this intermetallic compound grows under the solutal diffusion control. The calculated coupled zone demonstrates that (Co₂Si+CoSi) eutectic can form within certain undercooling regime, when the composition is in the range from 23.6% to 25.4% Si. And the calculated coupled zone of (CoSi+CoSi₂) covers a composition range from 40.8% to 43.8% Si.

关键词: Liquid-solid transition

Computational Comminution and Its Key Technologies Applied to Materials Processing Procedure

武汉理工大学学报-材料科学版(英文版)

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PHASE-FORMATION IN DROP-TUBE PROCESSING FROM UNDERCOOLED PD77.5AU6SI16.5 MELT

Journal of Materials Science

The Pd77.5Au6Si16.5 alloy was studied by drop-tube processing. Palladium solid-solution phase was found in smaller droplets (diameter D < 400 m), while in larger droplets, the intermetallic compound Pd3Si was observed. The difference in free energy between the undercooled liquid and the solid state, the activation energy for the formation of post-critical nuclei, the nucleation frequency and the crystal growth velocity, were calculated as functions of temperature for palladium solid solution and Pd3Si phases. These calculations led to time-temperature-transformation curves which were capable of describing the experimental findings on the kinetics of solidification of this alloy.

关键词: metallic glasses;solidification

Key Problems in Microforming Processes of Microparts

Chunju WANG , Debin SHAN , Bin GUO , Jian ZHOU , Lining SUN

材料科学技术（英文）

From the viewpoint of production engineering, microforming is considered as an effective process to fabricate various microparts. Several key problems in microforming processes were investigated. A new microforming apparatus with a high stiffness piezoelectric actuator as the punch driver was developed to produce microparts. To improve the forming abilities and locate the billets, a floating microdie was designed. The size effects of the billets and die cavities on the microforming abilities were studied with upsetting and coining tests, respectively. And the isothermal microforming process of microgears was performed with the developed microforming apparatus. Several analysis methods were used to evaluate the forming quality of the microparts.

关键词: Microforming , 尺寸效应 , 微塑性成形设备 , 浮动

Key R&D activities for development of new types of wrought magnesium alloys in China

Transactions of Nonferrous Metals Society of China

Many researchers in China are actively engaged in the development of new types of wrought magnesium alloys with low cost or with high-performances and novel plastic processing technologies. The research activities are funded primarily through four government-supported programs: the Key Technologies R&D Program of China, the National Basic Research Program of China, the National High-tech R&D Program of China, and the National Natural Science Foundation of China. The key R&D activities for the development of new wrought magnesium alloys in China are reviewed, and typical properties of some new alloys are summarized. More attentions are paid to high-strength wrought magnesium alloys and high-plasticity wrought magnesium alloys. Some novel plastic processing technologies, emerging in recent years, which aim to control deformation texture and to improve plasticity and formability especially at room temperature, are also introduced.

关键词: wrought magnesium alloy;microstructure;properties;alloy designing;plastic deformation;research projects;y-zr alloys;mechanical-properties;mg-4y-4sm-0.5zr alloy;grain-refinement;rare-earth;microstructure;gd;phase;temperature;evolution

EFFECT OF INTERMITTENT HIGH FREQUENCY MAGNETIC FIELD ON INITIAL SOLIDIFICATION IN CONTINUOUS CASTING

T. J. Li(Dalian University of Technology , Dalian 116923 , China)K. Sassa and S. Asai(Nagoya University , Nagoya 464-01 , Japan)

金属学报(英文版)

Contacting state between molten metal and a mold and initial solidification process of continuously cast metals can be controlled by imposing an intermittent magnetic field.In this study, effect of the intermittent magnetic field on the initial solidification ofcontinuoasly cast metals was investigated by measuring the temperature distribution in the melt pool and the initial solidification starting position of shells. It was found that under the condition with intermittent magnetic field, the melt near meniscns is in slow cooling state, the initial solidification starting position descends, initial solidification shell thickens and the liquid-solid interface becomes smooth.

关键词: continuous casting , null , null , null

The present status and key problems of carbon nanotube based polymer composites

Express Polymer Letters

The state-of-art and key problems of carbon nanotube (CNT) based polymer composites (CNT/polymer composites) including CNT/polymer structural composites and CNT/polymer functional composites are reviewed. Based on the results reported up to now, CNTs can be an effective reinforcement for polymer matrices, and the tensile strength and elastic modulus of CNT/polymer composites can reach as high as 3600 MPa and 80 GPa, respectively. CNT/polymer composites are also promising functional composite materials with improved electrical and thermal conductivity, etc. Due to their multi-functional properties, CNT/polymer composites are expected to be used as low weight structural materials, optical devices, thermal interface materials, electric components, electromagnetic absorption materials, etc. However, the full potential of CNT/polymer composites still remains to be realized. A few key problems, such as how to prepare structure-controllable CNTs with high purity and consistently dependable high performance, how to break up entangled or bundled CNTs and then uniformly disperse and align them within a polymer matrix, how to improve the load transfer from matrix to CNT reinforcement, etc, still exist and need to be solved in order to realize the wide applications of these advanced composites.

关键词: polymer composites;carbon nanotubes;mechanical properties;electrical;properties;thermal properties