The brittle-ductile transition in HIP consolidated near γ-TiAl + W and TiAl + Cr powder alloys

The properties, deformation microstructures and fracture characteristics resulting from tensile tests between 20 °C and 850 °C are compared for Ti-48Al-2W and Ti-47.5Al-3Cr. TiAl + Cr exhibits a brittle-ductile transition with an elongation at 20 °C of 2.2% increasing to 36% at 850 °C. A much less pronounced brittle-ductile transition exists for TiAl + W, with an increase in elongation from 1.3% at 20 °C to only 4.5% at 850 °C. In both alloys fracture occurs predominantly by transgranular cleavage at low temperatures, changing to intergranular and then prior particle boundary failure with increasing temperature. High densities of deformation twins and 12〈110] dislocations form in TiAl + Cr deformed at ⩾ 700 °C. For TiAl + W much less deformation twinning occurs, even during tensile deformation at 850 °C. The inability of TiAl + W to accommodate strain by deformation twinning eliminates the brittle-ductile transition that occurs for most near γ-TiAl compositions. TiAl + Cr attains higher fracture strength at 20 °C (563 MPa) than TiAl + W (505 MPa). This improved strength is related to the substructure developed during HIP consolidation. The increased 20 °C ductility of TiAl + Cr is associated with a more homogeneous as-HIPed microstructure.