Fabrication and characterization of Ti3SiC2-TiB2-(TiC)-SiC composites through carbosilicothermic reduction of leucoxene concentrate

Abstract

Dense Ti3SiC2–TiB2-(TiC)–SiC composites have been fabricated from leucoxene concentrate, a product of preliminary processing of titanium-containing sandstones, by a three-step technique. In the first step, Ti3SiC2–TiB2–SiC agglomerated powders substantially differing in SiC content were prepared by the method of the vacuum carbosilicothermic reduction (VCSTR) synthesis using SiC as a reductant and B4C additive as a solid boriding agent. The unwanted impurities were removed from the products of the VCSTR synthesis by leaching with hydrofluoric acid in the second step. In the third step, the purified Ti3SiC2–TiB2–SiC powders were hot-pressed in a graphite die under 30 MPa at 1500–1550 °C, resulting in nearly fully dense ceramics. The values of flexural strength and fracture toughness measured for the prepared leucoxene-derived ceramics fell in the ranges 450–600 MPa and 5.6–7.0 MPa m1/2, respectively, with the best results obtained for the sample with low SiC content. It was also shown that when SiC content was quite low, a part of Ti3SiC2 may have decomposed during the hot pressing step, resulting in the formation of the corresponding amount of TiC. These observations thus suggest that the presence of SiC particles in the composites play an ambivalent role, on the one hand, negatively affecting strength properties, but on the other hand, preventing the decomposition of Ti3SiC2 during the hot pressing step. According to the results obtained from analyses of microstructure and strength properties of the leucoxene-derived Ti3SiC2–TiB2-(TiC)–SiC composites fabricated through the VCSTR synthesis, it was concluded that these materials have high potential to be applied as a promising structural ceramics.