Pressure-assisted reactive synthesis of titanium aluminides from dense 50Al-50Ti elemental powder blends

In the present research, dense gamma-TiAl based intermetallic samples were fabricated by reactive synthesis of fully dense elemental 50 at. pet Al-50 at. pet Ti powder blends. Two different processing routes were attempted: thermal explosion under pressure (combustion consolidation) and reactive hot pressing. In both approaches, relatively low processing or preheating temperatures (less than or equal to 900 degrees C) were used. The entire procedure of thermal explosion under pressure could be performed in open air without noticeable oxidation damage to the final product. The application of a moderate external pressure (less than or equal to 250 MPa) during synthesis was shown to be enough to accommodate the negative volume change associated with TiAl formation from the elemental components and, thereby, to ensure full density of the final product. Microstructure and phase composition of the materials obtained were characterized employing X-ray diffraction and scanning electron microscopy with energy dispersive analysis. It was found that at elevated temperatures (e.g., 900 degrees C), the equiatomic 50Al-50Ti alloy lies beyond the homogeneity range of the gamma-TiAl phase in the Ti-Al binary and contains, in addition to gamma-TiAl, Al-rich Ti3Al. Mechanical properties of the materials synthesized were evaluated in compression tests at different temperatures and by microhardness measurements. Due to its very fine microstructure, the Ti-Al material synthesized via reactive hot pressing exhibited superplastic behavior at temperatures as low as 800 degrees C.