Synthesis and characterization of 0.3 Vf TiC-Ti3SiC2 and 0.3 Vf SiC-Ti3SiC2 composites

In this work, two composite compositions-one with 30% (v/v) SiC, the other with 30% (v/v) TiC, balance Ti3SiC2-were synthesized and characterized. Fully dense samples were fabricated by hot isostatically pressing Ti, SiC and C powders for 8 h at 1500 or 1600 degreesC and a pressure of 200 MPa. Both TiC and SiC lower grain boundary mobility in Ti3SiC2. Coarsening of the SiC particles was also observed. At comparable grain sizes, all composites tested were weaker in flexure than the unreinforced Ti3SiC2 matrix, with the reduction in strength being the worst for the SiC composites. This reduction in strength is most probably due to thermal expansion mismatches between the matrix and reinforcement phases. The composite samples were exceptionally damage tolerant; in one case a 100 N Vickers indentation (in a 1.5-mm thick bar) did not reduce the flexural strength as compared to an unindented or as-fabricated samples. The same is true for thermal shock resistance; quenching samples from 1400 degreesC in room temperature water, resulted in strength reductions that were 12% at best and 50% at worst. In the 25-1000 degreesC temperature range, the thermal expansion coefficients of the two composites were indistinguishable at 8.2 X 10(-6) K-1. The Vickers hardness values depended on load; at 100 N, the hardnesses were approximate to15 GPa; at 300 N, they asymptote to 7-8 GPa. For the most part, very few cracks emanate from the comers of the Vickers indents even at loads as high as 500 N. In the few cases where cracks did initiate, fracture toughness values were crudely estimated to lie in the 5-7.5 MPa rootm range. (C) 2003 Elsevier Science B.V. All rights reserved.