Combustion synthesis of TiC–TiB2 composites

Abstract

Abstract An experimental study on formation of TiC–TiB2 in situ composites with a broad range of compositions was conducted by self-propagating high-temperature synthesis (SHS) using the reactant compacts from different combinations of Ti, B4C, C, and B powders. Direct reaction of Ti with B4C at stoichiometry of Ti:B4C = 3:1 yields a TiB2-rich composite with TiC:TiB2 = 1:2. Formation of the products containing 20, 33.3, and 50 mol% of TiB2 was achieved by the Ti–B4C–C reactants. In addition, the test specimen composed of Ti, B4C, and B was employed for the synthesis of a composite with 80 mol% TiB2. Among three different types of the powder compacts, the boron-containing sample was characterized by the fastest combustion wave and the highest reaction temperature. The lowest combustion temperature and wave velocity were observed in the Ti–B4C compact. When fine Ni particles were added to the Ti–B4C reactant, it was found that the propagation rate of the reaction front was increased and the densification of the end product was enhanced significantly. This was attributed to formation of the Ti–Ni eutectic liquid during the reaction. As a result, the relative density of a TiC + 2TiB2 composite increases from 30 to 86% with the Ni content from 0 to 20 mol%. Based upon the XRD analysis, small amounts of TiNi3 and TiB were detected in the Ni-reinforced TiC–TiB2 composites.