Thermal expansion of metals reinforced with ceramic particles and microcellular foams
- PDF / 1,913,930 Bytes
- 18 Pages / 612 x 792 pts (letter) Page_size
- 33 Downloads / 207 Views
I.
INTRODUCTION
THE coefficient of thermal expansion (CTE) of metalmatrix composites can be tailored by varying the nature, volume fraction, and morphology of the reinforcement in the composite. This allows precise matching of the composite CTE with that of mating components, a possibility that is beginning to be exploited on an industrial scale in applications such as electronic packaging.[1,2] Although a basic physical property, the CTE of a metalmatrix composite is relatively difficult to predict, precisely because it is influenced by several factors. These include matrix plasticity and the internal structure of the composite, which is typically made of particles or fibers embedded in a continuous metallic matrix. With fiber reinforcements, it has been shown that matrix yielding caused by internal thermal stresses can cause permanent hysteretic deformation of the composite during stress-free thermal cycling, and that microcracks or fiber intrusion may form at specimen-free surfaces.[1,3–11] Comparatively, composites featuring isotropic reinforcements, such as SiC particle-reinforced aluminum, exhibit a simpler thermomechanical behavior, free of macroscopic thermal ratchetting phenomena found with fibrous reinforcements.[1] Thus, this class of metal-matrix composites has become the most prominent candidate for thermal applications. In an isotropic composite, microstructural variables include the reinforcement volume fraction, its size, and its morphology. The first variable is known to exert a strong and general influence on composite CTE. The second variable, the influence of which is expected to be system speD.K. BALCH, Research Engineer, Molten Metal Technology, Fall River, MA 02720. A. MORTENSEN and S. SURESH, Professors, and Y.-L. SHEN, Postdoctoral Research Associate, are with the Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139. T.J. FITZGERALD, Advanced Engineer, is with Westinghouse Electric Corporation, Orlando FL 32826. V.J. MICHAUD, Assistant Professor, is with Laboratoire de Me´canique des Sols, Structures et Mate´riaux, Ecole Centrale Paris, 92295 ChaˆtenayMalabry Cedex, France. Manuscript submitted February 15, 1996. 3700—VOLUME 27A, NOVEMBER 1996
cific because intrinsic thermal expansivity and elastic moduli are not size dependent, was shown to influence the CTE of XD* coherent TiC particle-reinforced Al compos*XD is a trademark of Martin Marietta Corporation, Bethesda, MD.
ites.[12] The article presented here is primarily an exploration of the last variable, namely, reinforcement morphology. Specifically, we investigate the role played by reinforcement continuity, which is expected to exert a significant influence on the thermal expansion of isotropic metal-matrix composites, as shown by micromechanical analysis of the thermal expansion of two-dimensional (2-D) SiC/Al composites.[13] This exploration is conducted experimentally, by comparing reinforcements of the following two types: (1) discrete SiC reinforcing elements at high volume
Data Loading...
