ALLOY DESIGN FOR IMPROVEMENT OF DUCTILITY AND WORKABILITY OF ALLOYS BASED ON INTERMETALLIC COMPOUND TIAL

Two drawbacks of TiAl, deficiency of room temperature ductility and difficulty of hot working have been surmounted substantially by the authors, and at present active research work of light heat-resisting TiAl-base alloys has been performed over a wide range from academic to technical fields aiming at practical uses. In this overview it is described that room temperature ductility is improved by the addition of Mn and, in connection with this improvement, concepts of the authors for the nature of TiAl and the roles of third elements which are soluble in TiAl are discussed. Drastical changes in microstructure by heat treatment and thermomechanical treatment, and methods for hot working TiAl are described. It is also shown that superplasticity occurs in TiAl alloys with the fine equiaxed alpha + gamma structure which is obtained by elaborate thermomechanical treatment.