Mechanical properties of the cast intermetallic alloy Ti-43Al-7(Nb,Mo)-0.2B (at %) after heat treatment

A new approach to obtaining fine-grained structure in intermetallic-compound alloys such as gamma-TiAl + alpha(2)-Ti3Al has been suggested. This approach is based on the use of alloys that solidify as the beta phase, which contain beta-stabilizing additives such as Nb and Mo and are characterized by the small size of crystallites already in the cast state; in these alloys, a simple heat treatment makes it possible to substantially decrease the fraction of the lamellar component and to increase the content of the beta(B2) phase. It is shown on the example of the Ti-43Al-7(Nb,Mo)-0.2B (at %) alloy that this heat treatment ensures superplastic properties in the material in the temperature range of T = 1050-1130C at a deformation rate (epsilon) over dot = 1.7 x 10(-4) K-1. Under these temperature-strain-rate conditions, relative elongations such as delta = 160-230% and low flow stresses such as sigma = 36-100 MPa characteristic of superplastic flow have been obtained. It has been shown for the first time for the intermetallic gamma-TiAl + ga(2)-Ti3Al alloy that a sheet semifinished product cut out from an ingot subjected only to heat treatment can have plasticity acceptable for press forming.