Beyond Orowan hardening: Mapping the four distinct mechanisms associated with dislocation-precipitate interaction

The conventional role played by precipitates in crystalline solids is in blocking the motion of dislocations and for consequentially hardening, a mechanism attributed to Orowan's finding. Recent experiments and theoretical analysis demonstrated that a few nanometre-sized pre-cipitates, when dispersed in advanced metals at fine spacing, can further boost their strength at no sacrifice in ductility. In this paper, we construct the deformation map of four distinct mechanisms associated with dislocation-precipitate interaction: at low-to-intermediate stress level, disloca-tions may loop around a precipitate or cut-through it. In both scenarios the precipitates harden the materials and there is no net gaining of dislocations. At high stress level, nanoscale pre-cipitates may in contrast act as dislocation sources and generate dislocations from the matrix-precipitate interface - an interface-nucleation process; or emit dislocations when highly stressed dislocations transverse them - a radiation-emission process. While the interface-nucleation mechanism could supply sustainable dislocation multiplication, the radiation-emission leads to the multiplication of two additional dislocations. Based on large-scale simula-tions and theoretical analysis, we construct a deformation map on dislocation-precipitate inter-action in terms of stress and precipitate size. The revealed mechanisms and the dislocation-precipitate interaction map pave the way for strength-ductility optimization in materials through precipitation engineering.