Formation of Compositional Gradient during Fabrication of FGMs by a Centrifugal in-situ Method Yoshimi Watanabe 1,a , Shin Oike 1 and Ick-Soo Kim 1,b 1 Department of Functional Machinery and Mechanics Shinshu University, 3-15-1, Tokida, Ueda 386-8567, Japan a yoshimi@shinshu-u.ac.jp, b kim@shinshu-u.ac.jp Keywords: Centrifugal in-situ method. Eutectic alloy. Intermetallics. Energy dispersive X-ray (EDX) analysis. Centrifugal force. Sedimentation. Abstract. The purpose of the present work is to study the formation of the compositional gradient during the fabrication of FGMs by a centrifugal in-situ method. Al-Al2Cu FGMs were fabricated by the centrifugal in-situ method using eutectic Al-33mass%Cu alloy, and the microstructures of fabricated FGMs were studied. It was found that the Al-Al2Cu FGMs could be fabricated by the centrifugal in-situ method from eutectic alloy. Based on the experimental results, the formation mechanism of the compositional gradient during the fabrication of FGM by the centrifugal in-situ method in the A-B alloy could be summarized as follows; 1) Partial separation of A and B elements in the liquid state occurs due to the density difference. 2) A compositional gradient is formed before the crystallization of the primary crystal. 3) The primary crystals in the matrix appear to depend on local chemical composition. 4) The primary crystals migrate according to density difference, and a further compositional gradient is formed. Introduction Casting under a centrifugal force is one of the most effective methods for fabrication of metal-based FGMs [1-12]. There are basically two types of fabrication methods of FGM under the centrifugal force. In the first type, the liquidus temperature of the master alloy is significantly higher than the processing temperature. Therefore, the dispersed phase remains solid in a liquid matrix during the centrifugal casting [4, 6], which we call a centrifugal solid-particle method [8]. The motion of solid particles in a viscous liquid can be simulated under a centrifugal force, because the molten metal is regarded as a viscous liquid that meets Stokes’s law. The gradient distributions of solid spherical particles in the FGMs fabricated by the centrifugal solid-particle method could be theoretically analyzed [3]. In the second type, the liquidus temperature of the master alloy is lower than the processing temperature. Therefore, centrifugal force can be applied during the solidification both to the dispersed phase and to the matrix [11, 12]. This solidification is similar to the production of in-situ composites using the crystallization phenomena, and therefore, we call a centrifugal in-situ method [12]. However, there is a lack of information on the origin of the compositional gradient in FGMs fabricated by the centrifugal in-situ method. In order to observe the effect of centrifugal force on compositional gradient during fabrication of FGMs by the centrifugal in-situ method, our experiments focus on eutectic Al-33mass%Cu alloy because it has no primary crystals. The microstructures of fabricated FGMs were observed with an optical microscope (OM) and a scanning electron microscope (SEM). Based on the experimental results, the origin of the compositional gradient in FGMs fabricated by centrifugal in-situ method is discussed. Materials Science Forum Vols. 492-493 (2005) pp. 693-698 online at http://www.scientific.net © 2005 Trans Tech Publications, Switzerland Licensed to Yoshimi Watanabe (yoshimi@giptc.shinshu-u.ac.jp) - Shinshu University - Japan All rights reserved. No part of the contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of the publisher: Trans Tech Publications Ltd, Switzerland, www.ttp.net . (ID: 160.252.158.199-07/03/05,20:59:20)