Wetting of ceramic particulates with liquid aluminum alloys: Part I. Experimental techniques
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I.
INTRODUCTION
M E T A L matrix composites are a family of advanced materials which may have attractive properties including high strength, high specific modulus, low coefficient of thermal expansion, good wear resistance, and attractive high-temperature properties. Composites also offer the opportunity to develop new materials with a unique set of properties that are not available with conventional materials. Discontinuous particulate or whisker reinforced aluminum alloy composites have a very desirable combination of high specific modulus and strength as well as good thermal stability. Compared with continuous fiber reinforced composites, discontinuous second phase reinforced composites provide improved ductility and reduced anisotropy in mechanical properties. Furthermore, the latter can be subjected to secondary working with conventional techniques, including extrusion and forging. Recently, particulates have been added to continuous fiber-reinforcod aluminum alloys to improve both longitudinal and transverse strength.r~J Casting of metal matrix composites is an attractive processing method since it is relatively inexpensive and offers a wide selection of materials and processing conditions. Good wetting is an essential condition for the generation of a satisfactory bond between solid ceramic phase and liquid metal matrix during casting of composites. In spite of the importance of wettability in the manufacture of composites, relatively few quantitative studies have been conducted and many fundamental questions remain unanswered. Since the wettability of fine ceramic particulates with liquid metal cannot be measured by such conventional methods as the sessile-drop test or by multiphase equilibrium, the first step of this research work was to develop a reliable and reproducible experimental technique for evaluation of wettability. The new technique is based on uniform packing of ceramic powder cylinders followed by pressure infiltration of liquid metal. Infiltration occurs when the P A V work done by the applied pressure balances the free energy S.-Y. OH, Research Associate, Department of Materials Science and Engineering, J. A. CORNIE, Principal Research Associate, Energy Laboratory, and K.C. RUSSELL, Professor of Metallurgy and Nuclear Engineering, are with Massachusetts Institute of Technology, Cambridge, MA 02139. Manuscript submitted October 9, 1987. METALLURGICAL TRANSACTIONS A
change due to replacement of the solid:vapor interface by a solid:liquid interface. The threshold pressure for infiltration may be used directly as a measure of wettability or may be converted to work of immersion or to a wetting angle by using a modified capillary force equation. Two commonly used ceramic particulates, SiC and B4C, and seven different aluminum alloys, pure Al, A1-2 pct Cu, A1-4.5 pct Cu, A1-2 pct Si, AI-4.5 pct Si, AI-2 pct Mg, and AI-4.5 pct Mg, were employed in this study. This paper describes the experimental technique and gives a few typical results. Results of the full study are given in the following pape
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