Hierarchical composites of B4C–TiB2 eutectic particles reinforced with Ti

Abstract

Eutectic particles of B4C–TiB2 were reinforced with Ti by spark plasma sintering (SPS) or infiltration. The SPSed samples with 20, 30 and 40 wt. % Ti consisted of ceramic phases, and had a bicontinuous macrostructure formed by the Ti-rich region and the eutectic particles region, while the infiltrated sample was a complex composite comprised of a 3D Ti-rich continuous network, composite in nature, that contained Ti-metal and in which are embedded isolated ceramic (eutectic) particles. The SPSed samples are brittle with the maximum bending strength of 300 MPa for the 30 wt. % Ti, higher than for a reference sample produced by SPS from directionally solidified eutectic particles. A higher amount of added Ti results in a higher displacement in the bending test suggesting a higher fracture toughness. Simultaneous strengthening and toughening of the composite was realized. The infiltrated sample was ductile, while its bending strength (220 MPa) was comparable to the values measured for the brittle as-introduced reference sample and the sample with 20 wt. % Ti, both produced by SPS. In the SPSed and infiltrated samples at the interface between the Ti-rich region and B4C–TiB2 eutectic particles, a local ‘pull-out’ intergranular fracturing mechanism mainly involving Ti–B 1D-grains was observed. This local micromechanism together with a ‘pull out’ macromechanism of the eutectic grains from the Ti-rich component are considered important for the bridging/anchoring behavior responsible for the strengthening and toughening processes in our novel hierarchical composites.