Effect of thermomechanical treatments on phase distribution and microstructure evolution of a Ti-48Al-2Mn-2Nb alloy

Titanium aluminide alloys based on TiAl offer potential benefits as intermetallics for structural applications due to their low density and attractive properties at high temperature. However, their strength and ductility are very dependent on microstructural morphologies and much research is being devoted to obtaining optimal properties. The large grain sizes and solute segregations associated with conventional castings have forced much of the work to be focused on obtaining finer microstructures, both in terms of grain sizes as well as lamellar spacings. Thermomechanical treatments have been used to produce a large variety of structural morphologies ranging from fully lamellar to duplex and equiaxed and in which the proportion of each phase is also variable. By choosing the correct temperature and strain rate parameters, it may be possible to modify the microstructure by dynamic recrystallization, if during the mechanical process the lamellae of the α2 phase can be broken down and be used to accelerate the kinetics of nucleation of the new γ grains. The present study has been carried out in order to examine this process and the authors have compared the different refined microstructures that can be obtained by a new thermomechanical process (ELIT pack-rolling) of a Ti-48Al-2Mn-2Nb alloy with respect to those obtained by heat treatments only