Microstructural and mechanical evaluation of near γ-TiAl alloys containing molybdenum and rhenium

Near-γ-TiAl alloys which incorporated Cr, and Mo or Re additions [Ti-48Al-2Cr-1.5Mo-0.1Y, Ti-48Al-2Cr-1.5Re-0.1Y, and Ti-46Al-2Cr-1.5Re-0.1Y(at.%)], were prepared by arc casting and hot isostatic pressing; then heat treated at 1,200 and 900 C to produce a duplex microstructure. All three alloys contained a bimodal size distribution of B2 phase, which was enriched in Cr+Mo or Cr+Re. Very little α2 was present in the 48Al alloys; whereas the 46Al, 1.5Re alloy contained areas of transformed lamellar α2/γ, within which short lengths of B2 periodically interrupted the α2 plates. The composition of both the equiaxed and lamellar γ in each alloy was 49 ± 0.5Al, 1.6±0.4Cr and ∼1.2Mo or <1Re(at%). Similarly, the composition of the B2 in the three alloys was experimentally equivalent: 33 ± 1Al, 8.5 ± 2Cr, and 0.5 ± 0.3Re. Room temperature tensile ductilities were low, ranging from 0.5 to 1%; while ultimate strengths approached 500MPa [7 x 10-4s-1 strain rate]. Testing at 700 C produced little change in alloy strength, while ductility increased to as much as 2.5%