WANG Yu
,
SONG Weixi
,
HAN Qiyong University of Science and Technology Beijing
,
Beijing
,
China The Institute of Precise and Special New Materials
,
University of Science and Technology Beijing
,
Beijing 100083
,
China
金属学报(英文版)
Size distribution and precipitation of VC particles in ferritic nodular cast iron have been examined by techniques of ultrasonic screening,small angle X-ray scattering and chemical dissolution.The VC particles are sized over a wide range.The superfine ones, dispersed in the ferritic matrix,are the majority.A saturated dispersion with ultrafine VC particles may be approached as the V content increasing in the iron.Thi5 seems to play an important role in the precipitation strengthening for ferritic nodular cast iron.
关键词:
nodular cast iron
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null
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null
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Shaoxiong ZHOU
材料科学技术（英）
The discovery of the first Fe-based ferromagnetic amorphous alloy in 1966 had made an impact on conventional magnetic materials because of its unique properties. Since then, a number of amorphous magnetic materials have been successfully developed and used in a wide variety of applications. A brief review of R & D activities on amorphous soft magnetic materials in China is given from the beginning to the present in a somewhat chronological order, followed by a brief introduction to their applications on electric and electronic industries. An analysis and a prospect of Chinese market of such amorphous materials are also presented.
关键词:
Bin GUO
,
Xiaodong XING
,
Huming DAI
,
Ronghua LUO
,
Zhongren WANG
材料科学技术（英）
A flexible special device for viscous pressure forming is designed and implemented. By using three proportional electro-hydraulic relief valves connected to a computer for precise control of releasing pressure of the medium, we can form differential pressure distribution in the die cavity. With the cooperation of programmable logical controller (PLC), computer and sensor modules in control system the device can satisfy all the requirements of the new forming process.
关键词:
Materials Letters
A new criterion of hardness is proposed based on the analysis of the bonding in fourteen rocksalt-structure solids with the aid of discrete variational Xalpha (DV-Xalpha) cluster calculations. The concept of bond density is introduced to measure the hardness of materials, and there is a good linear relation between bond density and Mohs hardness. Because the calculation does not involve any empirical parameters, it can be conveniently applied to some complicated systems for example, alloys and intermetallic compounds.
关键词:
Science in China Series a-Mathematics Physics Astronomy
In this paper, a new model to describe the dynamic ductile fracture is proposed. The constitutive relation of the elastic-viscoplastic matrix has an overstress form given by previous authors. A dynamic loading surface at constant equivalent strain rate(with the volumetric part also taken into account) is derived and an approximate expression for this dynamic loading surface is suggested. In the case where the porous material element is subjected to spherically symmetric tension, the Carroll-Holt's model and Johnson's model are recovered; and in the case where the strain rate sensitivity of the material tends to zero, the Gurson's model is recovered. Moreover, the normality condition of the plastic strain rate for the dynamic loading surface is discussed, and it is shown that the normality rule is no longer valid in general. Finally, comparisons of this model with the models recently proposed by Pan, Saje and Needleman as well as by Perzyna are also presented.
关键词:
ductile fracture;void growth;rate-sensitive material;solids;localization;fracture
P.Bian
,
Dong-Ying Ju
材料科学技术（英）
Magnetite (Fe3O4) of ferrite magnetic materials has attracted attentions arising by the chip coil electronic material. However, its industrial applications have been limited by the need of high temperature sintering under reduced pressure or vacuum. In order to develop the process method of low-cost and energy saving with high strength and high magnetism of the magnet, a new low temperature sintering method during CO2 gas and adding small amount of boric acid (H3BO3) are proposed. Here, the superfine magnetite powder was fabricated by decomposition from ferrous oxalate at 500℃ in CO2 gas. The ferrous oxalate was synthesized using iron chloride and ammonium oxalate with the liquid phase precipitation. The magnetite powder compact was produced by Newton press and CIP (cold isostatic press) after adding small amount of boric acid. In this study, the effects of the additive on the mechanical and magnetic properties of the sintered magnet were also evaluated. By characteristic evaluation of the magnet, the validity of the proposed new low-temperature sintering process and the optimal process conditions were confirmed.
关键词:
Ferrite magnet
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null
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null
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