Atomistic simulation of kink-pairs of screw dislocations in body-centred cubic iron

The nudged elastic band method is used to calculate the activation paths co nnecting jumps between the two degenerate states A and B of the screw dislo cation core in body-centred cubic (bcc) iron. Kink-pairs are found to be in volved in all such jumps. By comparing the activation energies, it is shown that the jump from state A to state B on the {101} plane is not the same a s that from B to A, and whichever is easier depends on the direction of the applied stress. This asymmetry results in a characteristic zigzag pattern of slip, and forms the basis of an explanation for pencil glide at elevated temperatures. The activation energy of the rate-determining jump is found to decrease with increasing stress, but the predicted flow stress is about three rimes greater than the experimental value at all temperatures. (C) 20 00 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights res erved.