Paper number 152

NANOSTRUCTURAL CHARACTERIZATION OF TERNARY CARBIDES IN CARBON-FIBRE REINFORCED MG-AL MATRICES AND THEIR INFLUENCE ON THE COMPOSITE PROPERTIES

A. Feldhoff, E. Pippel, J. Woltersdorf

Max-Planck-Institut für Mikrostrukturphysik, Weinberg 2, D-06120 Halle, Germany

Summary

To enhance the interface bonding in C/Mg-Al composites via the formation of aluminium carbides, the interface reactivity has been modified by changing the aluminium content of the matrix and by using carbon fibres with different surface microstructures. The particulars of the fibre/matrix interfaces as well as their influence on the mechanical properties have been explored by investigating the metal matrix composites on different structural levels using in situ three-point bending tests as well as chemical and structural transmission electron microscope analyses. With increasing interface reactivity three characteristic failure mecha-nisms have been observed (single-fibre fracture, bundle fracture, and brittle fracture), which could be related to different amounts of plate-shaped carbidic precipitates of varying size at the fibre/matrix interfaces of the composites. The bundle fracture at a medium reactivity provided the highest bending strength of approximately 929 MPa. Especially, the near-edge fine structures (ELNES) of electron energy-loss spectra have been analyzed to evaluate the bonding characteristics of the elements Mg, Al, and C, revealing that the precipitates at the fibre/matrix interfaces, which govern the composite properties, are not the binary carbides Al4C3 but ternary ones of approximate stoichiometry Al2MgC2.

Keywords

Al2MgC2, Al4C3, carbide formation, interface reactivity, high-resolution transmission electron microscopy, electron energy-loss spectroscopy, three-point bending, microstructure/property relationship.