MICROCRACKING IN B4C-TIB2 COMPOSITES

Boron carbide/titanium diboride composites with 20 and 40 vol% particu late TIB2 and various amounts of free carbon were investigated with re spect to microcrack toughening, In agreement with previous work, the m ere addition of TiB2 was found to raise the toughness from 2.2 MPa . m (1/2) up to 3.0 and 3.5 MPa . m(1/2), respectively. A further and very significant increase of composite toughness up to 6.0 MPa . m(1/2) wa s discovered upon the incorporation of free carbon. SEM and TEM observ ations reveal that this toughening is associated with microcracking at B4C-TiB2 phase boundaries. Microcracking is triggered by thin carbon interlayers, which are located at hetero interfaces and supply a weak fracture path.