Microstructure and properties of Al 2 O 3 -Al(Si) and Al 2 O 3 -Al(Si)-Si composites formed by in situ reaction of Al wi
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INTRODUCTION
RELATIVE to metals, ceramics typically have a high stiffness-to-weight ratio (specific modulus), good chemical and thermal stability, and good corrosion resistance. Metals generally have a high fracture toughness and are good thermal and electrical conductors. By combining a ceramic and a metal in a composite structure, the desirable properties of both can be realized, with the potential for tailoring composition and properties to specific applications. The prospect of making application-tailored composites with unique property combinations that improve functionality is appealing for many advanced engineering applications, including automotive, aerospace, and electronic packaging. However, despite their potential advantages, processing difficulties and economic constraints have largely limited the commercialization of ceramic composites. In recent years, considerable effort has been expended to develop more reliable and cost effective, reaction-based synthesis techniques for ceramic composites, v] Various in situ forming techniques have been used to fabricate ceramic-metal corn-
KEVIN G. EWSUK and S. JILL GLASS, Senior Members of Technical Staff, and RONALD E. LOEHMAN, Manager, University Programs and Advanced Materials Laboratory, are with Sandia National Laboratories, Albuquerque, NM 87185. ANTONI P. TOMSIA, Staff Scientist, is with Lawrence Berkeley Laboratory, Berkeley, CA 94720. WILLIAM G. FAHRENHOLTZ, Research Assistant Professor, is with the Department of Chemical and Nuclear Engineering, University of New Mexico, Albuquerque, NM 87106. This article is based on a presentation made in the "In Situ Reactions for Synthesis of Composites, Ceramics, and Intermetallics" symposium, held February 12-16, 1995, at the TMS Annual Meeting in Las Vegas, Nevada, under the auspices of SMD and ASM-MSD (the ASM/TMS Composites and TMS Powder Materials Committees). 2122--VOLUME 27A, AUGUST 1996
posites with high volume fractions of ceramic, including the directed metal oxidation (DIMOX*) process~2] and the *DIMOX is a trademark of Lanxide Corporation, Newark, DE.
reaction bonded alumina (RBAO) process, t31 Another relatively new and promising technique for in situ synthesis of ceramic-metal composites involves reacting molten aluminum with amorphous silica t4,5] or aluminosilicate ceramic preforms, t~j~ While all of these reaction synthesis techniques produce ceramic-metal composites with improved mechanical properties compared with single-phase ceramics, the latter method is particularly appealing in that it produces advanced composites using a combination of inexpensive precursor materials and traditional, inexpensive process technology. Reaction synthesis of ceramic-metal composites in the A1/SiO2 system has been reported by Matsuo and InabataI and by Breslin et al.IS] Matsuo and Inaba I41 made A1203AI(Si)-Si composites by reacting amorphous silica with molten aluminum at 900 ~ to 1000 ~ The reaction product was a mutually interpenetrating structure of - 7 0 wt pct A1203 and - 2 5 wt pct AI(Si), which s
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