Computer simulation of the core structure of the <111> screw dislocation in α-iron containing copper precipitates:: I. structure in the matrix and a precipitate Original Research Article

Strengthening due to small coherent BCC precipitates of copper is an important component of in-service irradiation hardening of ferritic pressure-vessel steels. The dislocation effects involved are studied here by atomic-scale computer simulation. Many-body interatomic potentials for the Fe–Cu alloy system are used to investigate stacking-fault-energy surfaces and to simulate the atomic structure of the <111> screw dislocation in both pure α-iron and the metastable BCC phase of copper. In iron, the core has the well-known three-fold form of atomic disregistry. In BCC copper, however, the core becomes delocalised by transformation of the copper as the lattice parameter is reduced to mimic the strain experienced by precipitates. Simulation of the screw dislocation threading through the centre of a BCC copper precipitate in an α-iron matrix shows that the extent of core delocalisation depends on precipitate size. The dislocation energy changes indicate a significant dislocation pinning effect due to this dislocation-induced precipitate transformation process.