Observation of planar stacking faults in a Ti-rich two-phase Ti-Al alloy after deformation at elevated temperatures

It is a common observation that in two-phase Ti-Al-based binary alloys, deformation of the gamma phase occurs by 1/2[110]-type ordinary dislocation activity and twinning associated with 1/6[112] type partials. In the present study the microstructure of a new Ti-Al-based alloy (Ti-47 at.% Al-2 at.% Mn-2 at.% Nb + 0.8 vol.% TiB2) with a duplex microstructure consisting of primary equiaxed gamma grains and lamellar alpha(2) + gamma colonies was studied by transmission electron microscopy (TEM) after deformation at elevated temperatures. Planar stacking faults were found in the gamma laths. A detailed contrast analysis by TEM shows that these planar stacking faults lying on (111) planes are bound by all the fee variants of the Shockley partial dislocations of type 1/6[121], in contrast with the observations in stoichiometric binary TiAl alloys, where only 1/6[112]-type Shockley partials are found to be associated with the true twins. It is proposed that the addition of ternary and quaternary elements such as Mn and Nb promotes the other variants of the fee-like dissociations (not common in L1(0) structure) in the present alloy.