Reaction synthesis of TiB<inf>2</inf>-TiC composites with enhanced toughness

Abstract

In situ toughened TiB2-TiCxcomposites were fabricated using reaction synthesis of B4C and Ti powders at high temperatures. The resulting materials possessed very high relative densities and well developed TiB2plate-like grains, leading to a rather high fracture toughness, up to 12.2 MPa•m1/2. The microstructure was examined by means of XRD, SEM, TEM and EDAX. The reaction products mainly consisted of TiB2and TiCx. No other phases, e.g. Ti3B4, TiB, Ti2B5and 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°C. The microstructural morphology is characterised by TiB2plate-like grains distributed uniformly in the TiCxmatrix. Some inclusions and defects were found in TiB2grains. 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 TiB2grains. © 2001 Acta Materialia Inc.