Invited Lecture
On the role of interface structure, morphology and misfit stresses in dislocation-precipitate interactions

The interactions between dislocations and precipitates can lead to significant strengthening of alloys. Using atomistic simulations, we show that the interaction mechanisms, and subsequently the hardening capacity of precipitates, are critically influenced by the nature of the interface and the misfit stress. In the case of an amorphous interphase boundary (IPB), as for Mg₁₇Al₁₂ precipitates in a Mg matrix, dislocations loop around the precipitate and get absorbed into the IPB. Although the situation is reminiscent of Orowan loops left in the matrix, the presence of dislocations in the IPB affects subsequent dislocation-interface interaction in a markedly different manner. The morphology, and in particular the curvature of IPBs, can furthermore drastically influence the misfit dislocation network, as demonstrated using experimentally obtained γ/γ’ interface morphologies in Ni-base superalloys. The local IPB orientation not only alters the misfit dislocation core structure, but can also facilitate the formation of ⟨100⟩ dislocations. Certain Ni-base superalloys furthermore form γ precipitates inside the cuboidal γ’ phase. Our simulations suggest that the misfit stresses caused by the γ precipitates reduce the yield stress of γ’ cubes subjected to nanomechanical compression tests. The situation is, however, different when the deformation is not controlled by the nucleation of dislocations. In this case, the γ precipitates lead to an additional hardening that is also observed experimentally. The different contributing factors are analyzed and a new potential strengthening mechanism is described.