Atomistic simulation of energetics of motion of screw dislocations in bcc Fe at finite temperatures

The nudged elastic band method is used to calculate the energetics of the kink-pair mechanism for the motion of 1/2〈1 1 1〉 screw dislocation cores in body-centred-cubic (bcc) iron. At low applied stresses, the critical event is found to be the expansion of the kink-pair while at high applied stresses, it is the nucleation of the kink-pair that is rate-controlling. The activation energy of the motion is found to decrease with increasing stress, but the predicted flow stress is about three times of the experimental value at all temperatures. The origin of this factor of 3 is discussed.