Effects of Ti/Al Ratio on Formation of Ti-Al Intermetallics/TiB2 Composites by SHS from Ti-Al-B Powder Mixtures

Abstract

Ti-Al intermetallics/TiB2 composites were prepared from elemental powder mixtures by the method of self-propagating high-temperature synthesis (SHS). Reactant mixtures were formulated to contain two parts; one group was (2Ti + 4B) to form 2TiB2 and the other group was (Ti + xAl) to produce Ti-Al intermetallic compounds. The content of Al ranged between x = 0.33 and 3.0, which was equivalent to the Ti/Al atomic ratio from Ti-25% Al to Ti-75% Al in the (Ti + xAl) group. The results showed that the increase of Al percentage reduced the overall combustion exothermicity and led to a slower self-sustaining combustion wave speed and a lower combustion temperature. Apparent activation energy of the Ti-Al-B solid-state combustion reaction was determined to be 114.7 kJ/mol by this study. Based on the XRD analysis, Ti-Al intermetallics/TiB2 composites featuring Ti3Al, TiAl, TiAl2, and TiAl3 as the dominant aluminide phase were respectively synthesized from the samples of Ti-25%~40% Al, Ti-50%~60% Al, Ti-71.4% Al, and Ti-75% Al. For the samples of Ti-25% Al and Ti-30% Al, Ti3Al was the only aluminide formed. The microstructure of the composites exhibited that TiB2 grains with a columnar shape of 2–3 μm in length were well distributed and embedded in the aluminide matrix. This study demonstrated an effective and energy-saving fabrication route for producing Ti-Al intermetallics/TiB2 composites with different dominant aluminide phases.