Structure and composition of ternary carbides in carbon-fibre reinforced Mg-Al alloys

The characteristics of the interlayers in metal matrix composites strongly influence the materials properties. We have investigated the formation of such layers in carbon-fibre reinforced Mg-Al alloys, produced via a gas-pressure melt-infiltration process. Results of high-voltage electron microscopy, high-resolution electron microscopy, selected area diffraction and electron energy loss spectroscopy with analysis of near-edge fine structures (ELNES) of the relevant ionization edges (Mg-L(23), Al-L(23), C-K, Mg-K and Al-K) revealed that ternary carbides of approximate composition Al(2)MgC(2) formed at the fibre/matrix interfaces. Analyses of ELNES point to a close relationship in terms of crystal chemistry between the ternary carbide Al(2)MgC(2) and the binary carbide Al(4)C(3). For Al(2)MgC(2), a structure is proposed, with metal atoms in a close-packed arrangement filled with carbon atoms in octahedral and trigonal-bipyramidal interstices.