Theoretical analysis of the particle gradient distribution in centrifugal field during solidification
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I.
INTRODUCTION
METAL matrix composites (MMCs) have played more and more important roles in the areas of aerospace,[1] automobile,[2] military,[3] and other industries[4] because of their excellent physical, mechanical, and tribological properties.[5] The methods to produce ceramic reinforced MMCs usually are powder metallurgy,[6] deposition techniques,[7] and casting techniques such as compocasting or rheocasting,[8] pressure infiltration,[9] squeeze casting,[10] stirring casting,[11] and centrifugal casting.[12,13] In the previously mentioned methods, casting techniques characterize excellent advantages such as lower cost, easier shaping, and simple operation.[14,15] The keys to cast particle reinforced MMCs are to disperse the particles in liquid and improve the distribution of dispersed particles in metal matrix. The electromagnetic stirring,[16,17] centrifugal[12,13] techniques are satisfactory to solve these problems. The functional gradient composite (FGC) is a new type of composite, which was first proposed by a Japanese scientist.[18] The FGC has become attractive because of its multifunctional properties, including the reinforced ceramic properties, matrix metal properties, and their combined properties. The main advantages of the FGC are the gradual change of properties such as coefficient of heat conductivity and electrical conductivity, thermal stress, etc. resulting from the gradient distribution of its structure and reinforced phases, which can avoid the destruction caused by the properties mismatch at high temperature.[19] The prediction of gradual distribution of particle and the design of structure of FGC are necessary to obtain special properties to meet the need of special use. The processing of particle reinforced FGCs is mainly done by vapor deposition,[20] powder metallurgy,[21] iso-ion spray techniques,[22] and self-propagating high temperature QINGMIN LIU, Assistant professor, YUANSHENG YANG, Vice Professor, and ZHUANGQI HU, Professor, are with the National Key Laboratory for RSA, Institute of Metal Research, Academia Sinica, Shenyang 110 015, China. YUNING JIAO, Assistant Professor, formerly with the National Key Laboratory for RAS, Institute of Metal Research, Academia Sinica, Shenyang 110015, China, is now with Tsinghua University, Beijing 100084, China. Manuscript submitted June 24, 1994. METALLURGICAL AND MATERIALS TRANSACTIONS B
synthesis,[23] which are hard to be applied in practical use due to the complex techniques and high cost. The present authors developed a new technique to produce particle reinforced FGCs by centrifugal casting. A theoretical analysis was made, and the factors that affect the gradient distribution of FGC are discussed in detail. II.
THEORETICAL ANALYSIS AND DISCUSSION
In the centrifugal field, particles in melt will move due to the existence of the density difference between the particle and liquid metal. The mold of centrifugal casting is of cylindrical shape. In order to simplify the calculation, assume that the solidification rate R of melt is constant
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