The complex bonding of titanium nitride layers in C/Mg composites revealedby ELNES features

TiN interlayers in carbon fibre reinforced magnesium were investigated usin g high-resolution electron microscopy (HREM), scanning transmission electro n microscopy (STEM) and electron energy loss spectroscopy (EELS), including analyses of near-edge fine structures (ELNES) and corresponding quantumche mical calculations. The nanocrystalline TiN fibre coatings of thicknesses b etween 10 and 30 nm were chemically vapour deposited from a TiCl4-N-2-H-2 a tmosphere. Detailed ELNES measurements across the fibre/matrix interregion with a point-to-point distance of 1.3 nm in combination with quantumchemica l calculations reveal in the fibre-near interlayer region interactions of t he Ti-3d electrons with both the N-2p and the C-2p electrons resulting in m ixed p-d-pi and p-d-sigma bondings. This hints to the formation of a TiC/Ti N mixture of varying composition or of a titanium carbonitride (TiCxNy) wit h a high carbon content at the fibre/coating interface during the first ste ps of the coating by interaction of the carbon atoms of the fibre surface w ith the reactor gas. In this way the excellent adhesion of the TIN layers o n the fibres can be understood which makes them appropriate for the importa nt application in Mg matrices, where the layers have to serve as a suitable coupling medium between fibre and matrix.