Sol–Gel Synthesis of Functionally Graded SiC–TiC Ceramic Material

Abstract

Functionally graded SiC–TiC composite materials are promising for using in the aerospace industry as relatively low-density materials. The production of such materials by the sol–gel synthesis of a finely divided titanium carbide matrix in the pore space of SiC frameworks was studied. It was demonstrated that the distribution of the TiC matrix in the space of the SiC framework can be changed by varying the composition of the coordination sphere of precursors. It was shown that, after eight cycles of hydrolysis of titanium-containing precursors in the presence of a phenol formaldehyde resin with subsequent carbonization and carbothermal synthesis (1400°C, dynamic vacuum, 2 h), the weight gains of the samples differed significantly: for the precursor [Ti(OC4H9)2.05(O2C5H7)1.95], which is more sensitive to moisture, it was 23%, and for the complex [Ti(OC4H9)1.95(O2C5H7)2.05], it was 37%. Moreover, in the former case, near-surface regions of the material were predominantly densified. It was noted that, with increasing content of the modifying phase TiC, the compressive strength increased, and the specific surface area decreased (as determined by low-temperature nitrogen sorption and mercury porosimetry). The obtained gradient of the composition of the SiC–TiC ceramics across the depth was confirmed by X-ray computed microtomography: the total porosity of the near-surface regions of the ceramics differed by a factor of 2.9.