Characterization of rapidly consolidated γ-TiAl

Abstract

A powder metallurgy-based rapid consolidation technique, Plasma Pressure Compaction (<TEX>$P^2C^{(R)}$</TEX>), was utilized to produce near-net shape parts of gamma titanium aluminides (<TEX>${\gamma}$</TEX>-TiAl). Micron-sized <TEX>${\gamma}$</TEX>-TiAl powders, composed of Ti-50%Al and Ti-48%Al-2%Cr-2%Nb (at%), were rapidly consolidated to form near-net shape <TEX>${\gamma}$</TEX>-TiAl parts in the form of 1.0" (25.4 mm) diameter discs, as well as <TEX>$3"{\times}2.25"$</TEX> (<TEX>$76.2mm{\times}57.2mm$</TEX>) tiles, having a thickness of 0.25" (6.35 mm). The <TEX>${\gamma}$</TEX>-TiAl parts were consolidated to near theoretical density. The microstructural morphology of the consolidated parts was found to vary with consolidation conditions. Mechanical properties exhibited a strong dependence on microstructural morphology and grain size. Because of the rapid consolidation process used here, grain growth during consolidation was minimal, which in turn led to enhanced mechanical properties. Consolidated <TEX>${\gamma}$</TEX>-TiAl samples corresponding to Ti-48%Al-2%Cr-2%Nb composition with a duplex microstructure (with an average grain size of <TEX>$5{\mu}m$</TEX>) exhibited superior mechanical properties. Flexural strength, ductility, elastic modulus and fracture toughness for these samples were as high as 1238 MPa, 2.3%, 154.58 GPa and 17.95 MPa <TEX>$m^{1/2}$</TEX>, respectively. The high temperature mechanical properties of the consolidated <TEX>${\gamma}$</TEX>-TiAl samples were characterized in air and vacuum and were found to retain flexural strength and elastic modulus for temperatures up to <TEX>$700^{\circ}C$</TEX>. At high temperatures, the flexural strength of <TEX>${\gamma}$</TEX>-TiAl samples with Ti-50%Al composition deteriorated in air by 10% as compared to that in vacuum. <TEX>${\gamma}$</TEX>-TiAl samples with Ti-48%Al-2%Nb-2%Cr composition exhibited better if not equal flexural strength in air than in vacuum at high temperatures.