BN interphases were synthesized by chemical vapour infiltration (CVI) from BCl3 and NH3 at 900 °C and 1200 °C within preforms made of a single 2D woven SiC fibre ply. Then CVI of a SiC matrix followed by molten silicon infiltration resulted in laboratory-made single-ply SiC/SiC-Si composites representative of similar industrial ceramic matrix composites. The interphases and interfaces were characterized by transmission electron microscopy. It has been found that, in the two cases, the interphases are mostly turbostratic BN. Those synthesized at 900 °C are very poorly crystallized and exhibit a quasi-isotropic microstructure. An equiaxed interlayer is obtained prior to the columnar CVI growth of SiC matrix. Interphases synthesized at 1200 °C exhibit high degrees of crystallization and structural anisotropy. The SiC matrix grows directly in columns on BN. For interphase thicknesses of 300 nm and more, triangular-shaped crystallites of rhombohedral BN appear in turbostratic BN and the columnar growth of SiC is disoriented.

Titanium oxides and carbides are often considered as electrode materials in energy conversion and storage devices due to their high potential conductivity and good stability. Titanium monoxide and titanium carbide have structures that can both be described as rocksalt with the same cubic close packed titanium sublattice with oxygen and carbon respectively occupying the octahedral interstices; however the oxide is characterised by extensive defects on both sublattices whilst the carbide is stoichiometric and might be considered as an interstitial metal. Despite the anticipated very different natures of the oxide and carbide sublattices, these two phases actually form a complete solid solution. In the present investigation, we carefully characterise this titanium oxycarbide solid solution, reporting on crystal structure, magnetic and electronic conduction properties. Titanium oxycarbide powders (TiO1-xCx with x = 0 ≤ x ≤ 1) have been prepared by solid state reaction of TiO and TiC powder under controlled environments at elevated temperatures. X-ray diffraction and pycnometric density measurements illustrate the gradual transition of crystal structure of titanium oxycarbides from vacancy containing rock-salt structure of TiO to the fully occupied TiC with increase in carbon content in the oxycarbide lattice. The variation of lattice parameter of oxycarbide crystal as a function of carbon content has been found to be non-linear which can be attributed to variations in the level of vacancies present in metal as well as non-metal sub-lattices.The existence of short-range ordering of anion vacancies in oxycarbide with a nominal composition of TiO0.5C0.5 where half of oxygen of TiO is replaced by carbon has been confirmed by selected-area electron diffraction studies. Low temperature magnetic and conductivity measurements confirm that all oxycarbide compositions are Pauli paramagnetic and good metallic conductors.

SiC/BN/SiC-Si single-ply composites with Hi-Nicalon S TM fibres were synthesised by chemical vapour infiltration and the liquid route. These are model composites representing the behaviour of industrial composites intended to be used as structural parts in the hot sections of aeronautical engines. Four interphases with two different degrees of crystallisation and, in each case, two different thicknesses were tested. The interfacial shear stress measured by fibre push-out test is significantly higher when the crystallisation degree of the BN interphase is low, yet in this case it decreases with the thickness of the interphase. This higher interfacial bonding is also associated, albeit less significantly, with better macromechanical properties as measured by tensile and shear tests. The cracks observed in the composite with different microscopy techniques are also less long and open. Depending on the interphases, the debonds are more or less pronounced and occur preferentially at different locations in the interfacial system.