The pinning of ½<1¯10] ordinary screw dislocations in γ-TiAl, which led to the characteristic trailing of dipoles in the microstructure, was studied. Although it was proposed that these could be variously intrinsic or extrinsic in nature, it was possible to rule out the former mechanism. This was done by means of very large scale three-dimensional atomistic simulations using the quantum mechanical bond order potential. It was found that the kink-pair formation energy was large 6eV, while the single kink migration energy was very small: 0.13eV. Using these and other atomistically derived data, kinetic Monte Carlo simulations were performed at realistic time- and length-scales in order to simulate dislocation mobility as a function of stress and temperature. Over the temperature range of the stress anomaly in γ-TiAl, it was determined whether one or more of the pinning and unzipping processes associated with the generation of jogs were observed during the simulations. It was concluded that the pinning of ordinary dislocations, and the anomalous mechanical behaviour, in γ-TiAl had to be attributed to a combination of extrinsic obstacles and extensive cross-slip in a crystal containing impurities.

Is the Pinning of Ordinary Dislocations in γ-TiAl Intrinsic or Extrinsic in Nature? A Combined Atomistic and Kinetic Monte Carlo Approach. I.H.Katzarov, A.T.Paxton: Acta Materialia, 2011, 59[3], 1281-90