FABRICATION AND CHARACTERIZATION OF TiAl/Ti3Al-BASED INTERMETALLIC COMPOSITES (IMCS) REINFORCED WITH CERAMIC PARTICLES

Dense (>95% of theoretical density) TiAl and Ti3Al based composites reinforced with 10-50 vol. % of B4C, TiC or TiB2 particles were successfully prepared by pressureless reaction sintering of reaction mixtures consisting of commercial titanium aluminide powders (TiAl and Ti3Al) blended with the appropriate amount of ceramic reinforcement. The green compacts made from the blended powder mixture were reaction sintered at 1300 degrees C for 2 h in an Ar+4 vol. % H-2-rich environment using a vacuum furnace. The morphology of the commercial powders and the microstructure of the as-sintered composites were studied by SEM-EDS and X-ray diffraction analysis. The mechanical properties were measured by tensile tests performed at room temperature. In the case of reactive systems (TiAl-B4C, TiAl-TiC and Ti3Al-B4C, Ti3AlTiC), densification proceeds via formation of various secondary bonding phases, whilst in non-reactive system (TiAl-TiB2 and Ti3Al-TiB2) the process seems to proceed by diffusion in liquid state. Regarding the room temperature tensile properties of the composites, superior improvement was observed in TiAl-B4C, TiAl-TiC and Ti3Al-B4C, Ti3Al-TiC samples with 50 vol. % of ceramic particles. However, in TiAl-TiB2 and Ti3Al-TiB2 samples the improvement was significantly lower, most probably due to the lack of chemical affinity between ceramic reinforcement and TiAl3 matrix.