Impact response of TiB₂-TiB composites

TiB₂-TiB composites with a TiB₂ content that varied between 100 and 36 wt% were synthesized from TiB₂ and Ti powder mixtures by the Spark Plasma Sintering (SPS) technique. The residual porosity, microstructure, phase composition and static mechanical properties of the composites (bending strength, hardness and fracture toughness) were determined using standard characterization techniques. The impact response of the composites has been studied in two series of planar impact experiments. In the first, the samples were shock loaded to an ultimate compressive stress of about 25 GPa in order to determine the materials Hugoniot elastic limit (HEL). In the second series, the composites were shock loaded by a modest, 3-4 GPa, compressive pulse with the purpose to define their spall strength. The experimental results show that both the static and the dynamic properties of the composites reflect their microstructure, residual porosity and phase composition, namely, the TiB₂ fraction in the composites. Even a limited Ti addition (5 wt%) in the starting mixture allows to synthesize by an SPS process at a relatively low temperature (1550 °C), composites with elevated mechanical properties, in particular high hardness (∼2400 HV). The addition of 50 wt% of Ti (36 wt% of TiB₂ in the composites) yields fully dense composites with a high fracture toughness (∼9.0 MPa m^0.5). The wide range of the static and dynamic properties of the TiB₂-TiB composites allows their tailor-design to specific applications.