The Complex Bonding of Titanium Nitride Layers in C/Mg Composites Revealed by ELNES Features

Abstract

TiN interlayers in carbon fibre reinforced magnesium were investigated using high-resolution electron microscopy (HREM), scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS), including analyses of near-edge fine structures (ELNES) and corresponding quantumchemical calculations. The nanocrystalline TiN fibre coatings of thicknesses between 10 and 30 nm were chemically vapour deposited from a TiCl 4 -N 2 -H 2 atmosphere. Detailed ELNES measurements across the fibre/matrix interregion with a point-to-point distance of 1.3 nm in combination with quantumchemical calculations reveal in the fibre-near interlayer region interactions of the Ti-3d electrons with both the N-2p and the C-2p electrons resulting in mixed p-d-π and p-d-σ bondings. This hints to the formation of a TiC/TiN mixture of varying composition or of a titanium carbonitride (TiC xNy) with a high carbon content at the fibre/coating interface during the first steps of the coating by interaction of the carbon atoms of the fibre surface with the reactor gas. In this way the excellent adhesion of the TiN layers on the fibres can be understood which makes them appropriate for the important application in Mg matrices, where the layers have to serve as a suitable coupling medium between fibre and matrix.