Reaction synthesis of TiB 2–TiC composites with enhanced toughness

Abstract

In situ toughened TiB 2–TiC x composites were fabricated using reaction synthesis of B 4C and Ti powders at high temperatures. The resulting materials possessed very high relative densities and well developed TiB 2 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 TiB 2 and TiC x. No other phases, e.g. Ti 3B 4, TiB, Ti 2B 5 and free Ti, were observed regardless of whether the starting composition was Ti:B 4C=3:1 or 4.8:1, and whether the sintering temperature was 1700 or 1800°C. The microstructural morphology is characterised by TiB 2 plate-like grains distributed uniformly in the TiC x matrix. Some inclusions and defects were found in TiB 2 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 TiB 2 grains.