Pore formation and compressive deformation in porous TiAl–Nb alloys containing directional pores

Porous Ti–xAl–8Nb (x = 45, 48, and 49 at%) alloys (i.e., intermetallic TiAl–Nb compounds) with cylindrical pores oriented along a single direction were prepared via unidirectional solidification in a hydrogen and helium gas atmosphere, while making use of the differences in the hydrogen solubilities of the liquid and solid phases of the alloys. The microstructures and pore morphologies of the alloys revealed that pore formation in the alloys was closely related to their solidification processes. In the case of the alloy with x = 45 at%, a primary solidified β (bcc) phase with high hydrogen solubility suppressed the formation of pores during solidification. On the other hand, in the case of the alloy with x = 49 at%, the formation of the primary β phase was suppressed, leading to the formation of elongated pores along the solidification direction. After being heat treated, the porous TiAl–Nb alloys exhibited a fully lamellar structure composed of α2-Ti3Al and γ-TiAl phases. These porous TiAl–Nb alloys with lamellar structures and directional pores exhibited superior compressive properties parallel to the direction of the pores.