Synthesis and characterization of 0.3 V sub f TiC-Ti sub 3 SiC sub 2 and 0.3 V sub f SiC-Ti sub 3 SiC sub 2 composites

• Published in: Journal of alloys and compounds Vol. 350; no. 1-2; pp. 303 - 312
• Main Authors: Ho-Duc, L H, El-Raghy, T, Barsoum, M W
• Format: Journal Article
• Language: English
• Published: 17.02.2003
• ISSN: 0925-8388

In this work, two composite compositions - one with 30% (v/v) SiC, the other with 30% (v/v) TiC, balance Ti sub 3 SiC sub 2 - 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 deg C and a pressure of 200 MPa. Both TiC and SiC lower grain boundary mobility in Ti sub 3 SiC sub 2 . Coarsening of the SiC particles was also observed. At comparable grain sizes, all composites tested were weaker in flexure than the unreinforced Ti sub 3 SiC sub 2 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 deg C in room temperature water, resulted in strength reductions that were 12% at best and 50% at worst. In the 25-1000 deg C temperature range, the thermal expansion coefficients of the two composites were indistinguishable at 8.2 x 10 exp -6 K exp -1 . The Vickers hardness values depended on load; at 100 N, the hardnesses were approx =15 GPa; at 300 N, they asymptote to 7-8 GPa. For the most part, very few cracks emanate from the corners 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 root m range.