In situ toughened TiB2-TiCx composites were fabricated using reaction synth
esis of B4C and Ti powders at high temperatures. The resulting materials po
ssessed very high relative densities and well developed TiB2 plate-like gra
ins, leading to a rather high fracture toughness, up to 12.2 MPa .m(1/2). T
he microstructure was examined by means of XRD, SEM, TEM and EDAX. The reac
tion products mainly consisted of TiB2 and TIG(x). No other phases, e.g. Ti
3B4, TiB, Ti2B5 and free Ti, were observed regardless of whether the starti
ng composition was Ti:B4C = 3:1 or 4.8:1, and whether the sintering tempera
ture was 1700 or 1800 degreesC. The microstructural morphology is character
ised by TiB2 plate-like grains distributed uniformly in the TiCx matrix. So
me 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 pr
operties. The main toughening mechanisms were likely to be crack deflection
, platelet pull-out and the micro-fracture of TiB2 grains. (C) 2001 Acta Ma
terialia Inc. Published by Elsevier Science Ltd. All rights reserved.