In-situ graphene platelets formation and its suppression during reactive spark plasma sintering of boron carbide/titanium diboride composites

Boron carbide composites with 10 vol.% TiB2 were prepared by reactive sintering of B4C, TiO2, and carbon black powder mixture at the temperature of 1800 °C, under a pressure of 70 MPa in a vacuum. The combined effects of electric current and in-situ reactions led to a significant overheating of the central part of the sample, while no overheating was observed for hot press and non-reactive SPS processes. A lower electrical resistivity of TiB2 produced a significant Joule heating of boron carbide, leading to its partial decomposition to form gaseous boron and graphene platelets. Homogenous, fully dense and graphene-free samples were obtained when employing an insulating Al2O3 paper during reactive SPS. A short dwell time (30 s after a degassing step of 6 min) and the uniform distribution of fine TiB2 grains were the main advantages of isolated SPS over the reactive hot press and SPS processes, respectively.