Unveiling dislocation characteristics in Ni3Al from stacking fault energy and ideal strength: A first-principles study via pure alias shear deformation

Abstract

Nickel aluminide $(\mathrm{N}{\mathrm{i}}_{3}\mathrm{Al})$ is an important material for a number of applications, especially when used as a strengthening constituent in high-temperature Ni-based superalloys. Despite this, there is minimal information on its mechanical properties such as strength, plasticity, creep, fatigue, and fracture. In the present work, a first-principles based pure alias shear deformation has been applied to shed light on dislocation characteristics in $\mathrm{N}{\mathrm{i}}_{3}\mathrm{Al}$ using the predicted stacking fault energy (i.e., the \ensuremath{\gamma} surface) and ideal shear strength $({\ensuremath{\tau}}_{\mathrm{IS}})$. Results include direct evidence for the splitting of a $1/2[\overline{1}10]$ dislocation into two Shockley partials on the ${111}$ plane, which is further supported by the equivalence of the complex stacking fault (CSF) energy ${\ensuremath{\gamma}}_{\mathrm{CSF}}$ and the antiphase boundary (APB) energy ${\ensuremath{\gamma}}_{\mathrm{APB}111}$. Estimates of the Peierls stresses using ${\ensuremath{\tau}}_{\mathrm{IS}}$ and elastic properties suggest the prevalence of edge dislocations in Ni and screw dislocations in $\mathrm{N}{\mathrm{i}}_{3}\mathrm{Al}$, agreeing with experimental observations regarding the dominance of edge dislocations in the first stage of crystal deformation in fcc metals and the yield-strength anomaly related to screw dislocations in $\mathrm{N}{\mathrm{i}}_{3}\mathrm{Al}$. The present calculations further point out that the CSF and APB111 are easily formed by shear due to the low-energy barriers, although the lowest planar energies are for the superlattice intrinsic stacking fault and the APB001. Through the case of $\mathrm{N}{\mathrm{i}}_{3}\mathrm{Al}$, the present work demonstrates that the pure alias shear methodology is not only computationally efficient but also provides valuable insight into the nature of shear-related properties.