The Realization of Synergistic Strength-Plasticity Effect for NiAl Nanocrystal by Modulating Twin and Grain Boundary

Ni-based alloys are widely used in aerospace applications due to their excellent strength and corrosion resistance, but high strength comes with a loss of plasticity, so a balance of strength and plasticity is critical. In this study, a heterogeneous microstructure (HS) material containing nanotwin crystals is designed to optimize the high strength and plasticity of Ni-based alloys by molecular dynamics simulations. The results show that when the pinch angle is greater than 45.29°, the hindering effect of twin boundaries (TBs) on dislocation slip is enhanced, and the tensile strength and modulus of elasticity increase with the increase of the pinch angle. Twin-polycrystalline NiAl alloys exhibit higher strength and plasticity synergies compared to pure polycrystalline and single crystals. The reduction in grain size leads to the opposite Hall-Petch behavior, where grain boundary (GB) slip dominates the deformation, reduces the strength, triggers local softening, and weakens the effect of conventional GB strengthening. The decrease in the spacing of the TBs has a strengthening effect on the nanocrystals. The competitive mechanism of twins and GBs determines the plastic deformation mode of NiAl nanocrystals. This study provides an important theoretical basis for the design of high-strength-plasticity Ni-based alloys.