Preparation and some properties of chemically vapour-deposited Si3N4-TiN composite

Chemically vapour-deposited (CVD) Si₃N₄-TiN composite (a plate with the maximum thickness of 1.9 mm) has been prepared on a graphite substrate using a mixture of SiCl₄, TiCl₄, NH₃ and H₂ gases. The CVD was carried out at deposition temperatures,T_dep, in the range of 1050 to 1450 ° C, total gas pressures,P_tot, from 1.33 to 10.7 kPa and gas flow rates of 136 (SiCl₄), 18 (TiCl₄), 120 (NH₃) and 2720 (H₂) cm³ min^–1. The deposits thus obtained appeared black. The Ti content in the composites ranged from 2.1 to 24.8 wt % and was found in the form of Tin. The structure of the Si₃N₄ matrices varied from amorphous (initially) to the- and-type, with increasingT_dep. Most of the- and-type deposits had a preferred orientation (001) parallel to the deposition surface. While the deposition surface of the amorphous deposits showed a pebble structure, the surfaces of the- and-type deposits were composed of various kinds of facets. The heat-treating experiment suggested that-Si₃N₄ obtained in the present work was formed directly via a vapour phase, and not from crystallization of amorphous Si₃N₄ or from transformation of-Si₃N₄.