871 STUDY OF INTERFACES IN XDTm AI/TiCP METAL MATRIX COMPOSITES R. Mitra, W.A. Chiou, J.R. Weertman, M.E. Fine and R.M. Aikin,Jr.* Department of Materials Science and Engineering Northwestern University, Evanston, Il 60208 *Martin Marietta Laboratory, Baltimore, MD 21227 ABSTRACT The metal-ceramic interface in an XD' Al/TiCP metal matrix composite has been characterized in as-extruded, recrystallized, and high temperature heat-treated conditions. In both the as- extruded and recrystallized composite, the interface is atomically abrupt. Localized orientation relationships exist between Al and TiC that lead to some degree of coherency at the interface. Recrystallization produces semicoherent interfaces by formation of subgrains in the Al adjacent to the TiC particles. Few interfaces show cracking, even after extensive deformation. Lack of cracking together with the direct contact down to atomic level, observed between the two phases are evidence for excellent bonding between the carbide particles and the aluminum matrix. Heat treating samples at 913 K for 24 hours produces reaction products like AI 3 Ti and A1 4 C 3 . These reactions are explained on the basis of thermodynamic data. INTRODUCTION In recent years there have been many studies on solid state metal-ceramic interfaces, with emphasis on structure and chemistry on an atomic scale [1-2]. Very little, however, is known about the structural aspects of specific interfaces in particulate metal-matrix composites. It is a well known fact that the interfaces play an important role in the performance of composites. The nature of the bonding and the interfacial energy are functions of the structure and chemistry of the interfaces on an atomic scale. Thermodynamic stability of the interface also is of interest. The processing parameters of course influence the nature of the interface obtained in commercial composites. This paper reports a study of the metal-particulate interfaces in an Al/TiC. composite prepared at Martin Marietta Laboratories, Baltimore, Maryland, by the XDTM process [3] . Both Al and TiC have a fcc lattice. TiC is partly ionic [4] and has a NaCl structure. The present work is a qualitative study of the structure observed at the interface in order to understand the nature of the interfacial bonding. The thermodynamic stability of the interface has also been examined. MATERIAL Aluminum with 15 volume percent TiC, of 0.7 pm average particle diameter, was produced by a two step process. First, TiC was precipitated in situ in molten Al via the XD T ' process; this step produced a high volume fraction "master alloy". In the second step, the XDTM master alloy was diluted with 99.99% pure aluminum and cast into a 75 mm diameter mold. This ingot was then extruded at 648 K with a 27:1 extrusion ratio. The TiC particles Mat. Res. Soc. Symp. Proc. Vol. 238. 01992 Materials Research Society terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/PROC-238-871 Downloaded from https://www.cambridge.org/core. IP address: 44.200.194.182, on 21 Feb 2022 at 20:46:17, subject to the Cambridge Core