Microstructures and properties of investment castings of γ-titanium aluminide

gamma-TiAl castings have been produced by induction skull melting (ISM), and their micro structures, hardness and tensile properties have been studied in the as-cast, hot isostatically pressed (HIPped) and HIPped + heat treated conditions. The equiaxed rosette grains found in the cast structure suggest that the alloy was cast in a partially solid condition. HIPping and heat treatment for 24 h at 1300 degreesC resulted in a duplex structure and decreased the hardness and tensile properties compared with the as-HIPped condition. The hardness and tensile properties also decreased with increasing bar diameter. The main fracture modes in duplex structures were transgranular (TG) in equiaxed gamma-grains and translamellar (TL) in lamellar grains. The presence of an alpha(2)/gamma lamellar structure can improve strength and ductility. (C) 2002 Elsevier Science B.V. All rights reserved.