A 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 degreesC according to the reaction. B4C + TiO2 --> B4C1-x + TiB2 + CO up arrow (or CO2 up arrow). Above 2000 degreesC, the resulting two-phase, B4C1-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 degreesC for 1 h a 95% dense, fine-grained composite material, consisting of substoichiometric B4C1-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. (C) 2000 Elsevier Science Ltd. All rights reserved.