Reaction synthesis of TiB2-TiC composites with enhanced toughness

In situ toughened TiB2-TiCx composites were fabricated using reaction synthesis of B4C and Ti powders at high temperatures. The resulting materials possessed very high relative densities and well developed TiB2 plate-like grains, leading to a rather high fracture toughness, up to 12.2 MPa .m(1/2). The microstructure was examined by means of XRD, SEM, TEM and EDAX. The reaction products mainly consisted of TiB2 and TIG(x). No other phases, e.g. Ti3B4, TiB, Ti2B5 and free Ti, were observed regardless of whether the starting composition was Ti:B4C = 3:1 or 4.8:1, and whether the sintering temperature was 1700 or 1800 degreesC. The microstructural morphology is characterised by TiB2 plate-like grains distributed uniformly in the TiCx matrix. Some inclusions and defects were found in TiB2 grains. The very high reaction temperature was believed to be responsible for the formation of plate-like grains, which, in turn, is responsible for the much improved mechanical properties. The main toughening mechanisms were likely to be crack deflection, platelet pull-out and the micro-fracture of TiB2 grains. (C) 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.