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The influence of interaction geometry on the obstacle strength of voids and copper precipitates in iron

Interaction between a 1/2⟨1 1 1⟩{1 1 0} edge dislocation and voids or coherent bcc Cu precipitates (diameter D = 2 or 4 nm) in Fe with their centre displaced by ±Δz from the dislocation glide plane is investigated by computer simulation for temperature T = 0 to 450 K. Voids provide the highest critical stress, τc, when Δz = 0. The dislocation climbs up on release when Δz ⩾ 0, but down when Δz < 0. Void-surface facets influence the sense of climb. There is no correspondence between τc and the sense or magnitude of climb. 2 nm precipitates give highest τc when Δz < 0 and lowest when Δz > 0, due to a combination of the modulus difference and size misfit between bcc Cu and Fe. 4 nm precipitates are partially transformed to fcc structure by the dislocation when T ⩽ 300 K and Δz ⩾ 0. Surprisingly, the transformed fraction of Cu at low T is highest for Δz = D/2, due to the compressive field of the dislocation. The geometries that produce large transformed fractions result in the lowest τc, in contrast to expectation from previous studies.