Directional solidification of TiAl-Si alloys using a polycrystalline seed

Directional solidification (DS) process of Ti'43Al-3Si alloys has been stud ied. Successful DS ingots having not only fully lamellar microstructure par allel to longitudinal axis but also rotated columnar grains with respect to longitudinal axis were obtained using a polycrystalline seed material. Suc cessful seeding and growing require plane-front solidification condition du ring the entire DS process. Fracture toughness of the DS alloys were superi or to the PST alloys, with a value of K-Q = 21.7-31.7 MPa (m)(1/2) for the crack arrest/divide mode and K-Q = 7.4-19.0 MPa (m)(1/2) for the short tran sverse mode. The orientation dependence of fracture toughness for the crack arrest/divide mode was improved in the DS alloy compared to the PST alloy. (C) 2000 Elsevier Science Ltd. All rights reserved.