SiC/SiC minicomposites with (PyC/TiC)n interphases processed by pressure-pulsed reactive CVI

(Pyrocarbon/titanium carbide)_n multilayered interphases were prepared within SiC/SiC minicomposites by a new method: pressure-pulsed reactive chemical vapour infiltration (P-RCVI). This method combines P-CVI with reactive chemical vapour deposition (RCVD). Minicomposite tensile tests with unload-reload cycles have shown that the interfacial shear stress depends on the number of TiCl₄ gas pulses used for the processing of TiC sub-layers. TEM observations have shown, that with a few gas pulses, the carbide nucleates as isolated grain islands which disturbs the structural anisotropy of the pyrocarbon. This structure results in a good mechanical fibre/matrix load transfer. By increasing the number of gas pulses, the TiC sub-layers become continuous and it is possible to partially consume the highly ordered pyrocarbon sub-layers, but, in that case, the load transfer is poor. The specimen behaviour in air at 700°C under a constant tensile loading was assessed. Compared with a pure pyrocarbon reference interphase, the interphases containing TiC significantly improve the lifetime of the SiC/SiC minicomposites.