Novel approach for the preparation of B₄C-based cermets

Additions of TiO₂ affect significantly the sintering behavior of B₄C. The two powders react at approximately 1500°C according to the reaction: B₄C + TiO₂ → B₄C_1-x + TiB₂ + CO ↑ (or CO₂ ↑). Above 2000°C, the resulting two-phase, B₄C_1-x + TiB₂, mixture sinters at a higher rate than the single-phase boron carbide. The rate of sintering increases dramatically for mixtures that contained initially 40 wt% TiO₂, yielding after sintering at 2190°C for 1 h a 95% dense, fine-grained composite material, consisting of substoichiometric B₄C_1-x and TiB₂. The boron-rich carbide displays very high affinity to carbon and reverts rapidly to stoichiometric composition when treated at high temperature in a carburizing atmosphere. The two-phased ceramic can be sintered to various levels of density and infiltrated with a molten metal. After infiltration with molten aluminum, the hardness of the resulting cermets ranges from 800 to 2500 HV and the flexural strength varies from 750 to 350 MPa depending on their ceramic-to-metal ratio.