The Interface Structure in Graphite/ Aluminum Composites

Abstract

-- _C--Transmission electron diffraction and Auger electron spectroscopy studies of the interfaces of selected graphite/ aluminum composite systems revealed that generally titanium diboride, (TiP,), ;ind aluminum oxide, (4-Al ), were present as the interfacial phases.The grain size and the crystallographic structure of these interfacial phases were studied and are discussed in terms of the transverse fracture behavior of the graphite/aluminum composites. The graphite fiber reinforcement/metal matrix composites are of great interest bcause of their high strength and potential for large-scale production and use. Aluminum alloys appear promising as matrix materials for graphite reinforced metal.In the majority of cases the fiber is pretreated followed by controlled immersion into molten aluminum to make the metal matrix composite"'. Even as this liquid metal infiltration technology advanced, the transverse strength of graphite-al ulninUm compos ites remained poor in contrast to the high strength in the longitudinal direction. A recent studyr indicated that the transverse behavior should be closely related to the interfacial properties. This interface could be the reaction zone between aluminum and fiber or the reaction zone between pretreatment coating and either the fiber or matrix.Some variations in the treatment of graphite fibers have been developed [3] , and the transverse strength has been improved without significant degradation of the longitudinal strength. But the basic understanding of the crystal structure of the interface phases is still lacking.The aim of the present work was to obtain crystallographic information about the interface reaction zone using electron diffraction in a Transmission Electron Microscope (TENI).The corresponding interface clIemi stry on some specimens was studied usini a Scanning: Auger Microscope (SAM).Various compos i te mate r i a I s wi t h di fferent transverse strengths were employed in order to correlate the structure of interface phase with mechanical properties.Titanium diboride (TIP,) was found in the interface layer for every material processed by the standard pretreatment coatin e. y-Auminum ox ide ly-Al)o phase was also observed in most materials studied here as were other oxides and carbides. ExperimentalThe graphite/aluriinum composite materials examined in this study are listed in Table 1 along with fiber type, transverse strength and the interface phases observed in TEM.Except for G5A42 which is plate consolidated from T133 wire, the materials are all unconsolidated wires. The matrix material is 0(101 Al.The single fiber wire in Table 1 is a single graphite fiber "pepreg" with no pretreatment coating on the interface. This composite wire is produced by the ion vapor deposition of an aluminum 4', Mg alloy on the fiber. liasically, two fiber types were examined in this study, each representing currently availiable commercial forms.One is a low modul us type 11 PAN fiber with the oriented graphite basal planes tendini.' to be parallel to the fiberThe o t...