Mechanisms of hardening due to copper precipitates in -iron

A comprehensive atomic-level simulation study has been made of interactions between a moving edge dislocation and copper precipitates that are initially coherent with the body-centred-cubic matrix of alpha-iron. Precipitates with diameter, D, in the range 0.7-6 nm have been considered over the temperature range 0-600 K. For some combinations of temperature and D, the critical applied resolved shear stress, c, at which the dislocation overcomes a row of precipitates with centre-to-centre spacing, L, is consistent with an elasticity treatment for strong obstacles, e.g. c is proportional to L-1 and ln(D). This has a specific atomic-level origin, for the proportionality holds when the dislocation induces a partial transformation of the copper towards the more stable face-centred-cubic phase. The driving force for the transformation increases with decreasing temperature and increasing D, and so c has a strong temperature-dependence for large D. The results of these simulations, which employ a set of interatomic potentials of Finnis-Sinclair type, are seen to correspond well with experiments carried out elsewhere.