Interface dominated deformation mechanisms in two-phase fcc/B2 nanostructures: Nishiyama-Wasserman vs. Kurdjumov-Sachs interfaces

Crystallographic orientation relationship (OR) in two-phase alloy microstructures determines their heterophase interfacial structures, and may influence their corresponding deformation mechanisms. Here, using prototypical fcc-Ni and bcc-ordered B2-NiAl phases, we have compared and contrasted the effect of fcc/B2 Nishiyama-Wasserman (NW) and Kurdjumov-Sachs (KS) heterophase interfaces on the deformation mechanisms prevalent in fcc-B2 nanostructures. For this purpose, we have uniaxially deformed fcc-B2 bicrystals, and multicrystals containing B2 lamellae via molecular dynamics (MD) simulations. The NW and KS interfaces acted as source and sink for fcc and B2 dislocations, and were susceptible to shearing via fcc twins. However, both interfaces differed in their ability to influence deformation mechanisms, and maintain interfacial structure under the influence of shear stresses. Inside the fcc phase, NW interfaces preferentially promoted stacking fault tetrahedra formation during the early stages of plastic deformation, while KS interfaces facilitated {111}< 112 >(fcc) twining. B2 dislocation plasticity also appears to have been affected. We also learn that the {111}(fcc) NW interface is highly sensitive to shear stresses, and after prolonged deformation it's interfacial structure closely resembled deformed {111}(fcc )KS interface. Mechanistic insights gained from MD is expected to inform alloy design approaches that aims to control the relative fractions of Nishiyama-Wasserman and Kurdjumov-Sachs interfaces.