Computer simulation of the core structure of the ⟨111⟩ screw dislocation in α-iron containing copper precipitates:: II.: dislocation-precipitate interaction and the strengthening effect

The small, coherent BCC precipitates of copper that form during fast-neutron irradiation of ferritic steels are an important component in the irradiation hardening that occurs during service. The conventional explanation of hardening due to copper precipitates is given in terms of the Russell-Brown (M. Acta Metall. 20 (1972) 969) modulus hardening model, in which precipitates are treated as soft spots in iron. In the present paper, the core structure and energy of a [111] screw dislocation are computed as it approaches a row of precipitates. The results indicate that the hardening observed in experiments is due to the effect of the screw dislocation core on the BCC copper structure rather than elastic interaction. This is a new precipitate strengthening effect. The increase in the flow stress is estimated from the interaction energy between the dislocation and the precipitate row, and the estimated value for precipitates of a size and spacing found in irradiated reactor pressure vessel steels is encouragingly close to that found experimentally. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.