Directional solidification of TiAl–Si alloys using a polycrystalline seed

Directional solidification (DS) process of Ti–43Al–3Si alloys has been studied. Successful DS ingots having not only fully lamellar microstructure parallel to longitudinal axis but also rotated columnar grains with respect to longitudinal axis were obtained using a polycrystalline seed material. Successful seeding and growing require plane-front solidification condition during the entire DS process. Fracture toughness of the DS alloys were superior to the PST alloys, with a value of KQ=21.7–31.7 MPa (m)1/2 for the crack arrest/divide mode and KQ=7.4–19.0 MPa (m)1/2 for the short transverse mode. The orientation dependence of fracture toughness for the crack arrest/divide mode was improved in the DS alloy compared to the PST alloy.