Deformation of Ti-56At.%Al single crystals oriented for single slip by 1/2<110] ordinary dislocations

Anomalous hardening by single (111) slip of ordinary dislocations (1/2[110]) has been investigated using gamma -Ti-56Al single crystals. The uniaxial compressive deformation was conducted in four different orientations, [(3) over bar 12 7], [(1) over bar 6 3], [(1) over bar 12 5] and [(1) over bar 7 2] between 196 K and 1173 K. It was found that the single slip of ordinary dislocations in this alloy occurred in three different orientations, [(3) over bar 12 7], [(1) over bar 6 3] and [(1) over bar 12 5] between 673 K and 1073 K. Strong orientation dependence in CRSS for the three deformation orientations is associated with the magnitude of the Schmid factor for cross-slip in the (110) plane. The dislocation structure of the deformed specimens showed that the cross-slip in the (110) plane increased with temperature in all three orientations. The main dislocation structures from (110) cross-slip at these temperatures were double cross-slip configurations, dipoles and dislocation loops. The anomalous hardening by ordinary dislocations at high temperatures can be explained well by the (110) cross-slip model. Based on the model, the activation energy for the (110) cross-slip was found to be 0.45 eV. In addition, the Cottrell-Stokes type temperature-change experiments were conducted under the single slip of ordinary dislocations at 673 K and 873 K. The results show that the yielding behavior isn't thermally reversible probably due to (110) cross-slip in this alloy. (C) 2000 Published by Elsevier Science Ltd on behalf of Acta Metallurgica Inc.