Ordinary dislocation configurations in high Nb-containing TiAl alloy deformed at high temperatures

High Nb-containing TiAl (Nb-TiAl) alloys possess mechanical properties at elevated temperatures superior to conventional TiAl alloys. However, the strengthening mechanisms induced by Nb addition have been discussed controversial for a long time. In the present study, the dislocation structures in a polycrystalline high NbTiAl alloy after tensile tests at 700 and 900 degrees C were investigated by transmission electron microscope (TEM) observation. The results show that abundant double cross slip of ordinary dislocations is activated in the samples deformed at 700 degrees C. The dislocations are pinned at the jogs and numerous dipoles are observed. Debris can be commonly observed in the vicinity of screw dislocations. Trace analysis shows that the cross-slip plane is (1 1 0)gamma at 700 degrees C but (1 1 1)gamma octahedral plane at 900 degrees C. Three-dimensional (3D) dislocation structures, caused by cross-slip and annihilation of ordinary dislocations, were observed along the screw orientation. The dipoles and debris produced by high-temperature cross slip can be important for the strengthening of high Nb-TiAl alloys.