Asymmetry in structural and thermo-mechanical behavior of intermetallic NiAl nanowire under tensile/compressive loading: A molecular dynamics study

The asymmetric stress-strain behavior under tension/compression in an initial 〈100〉 B2-NiAl nanowire is investigated considering two different surface configurations i.e., 〈100〉/(0 1 0) (0 0 1) and 〈100〉/(0 1 1) (0 −1 1). This behavior is attributed to two different deformation mechanisms namely a slip dominated deformation under compression and a known twinning dominated deformation under tension. It is also shown that B2 → BCT (body-centered-tetragonal) phase transformation under tensile loading is independent of the surface configurations for an initial 〈100〉 oriented NiAl nanowire. Under tensile loading, the nanowire undergoes a stress-induced martensitic phase transformation from an initial B2 phase to BCT phase via twinning along {110} plane with failure strain of ∼0.30. On the other hand, a compressive loading causes failure of these nanowires via brittle fracture after compressive yielding, with a maximum failure strain of ∼−0.12. Such brittle fracture under compressive loading occurs via slip along {110} plane without any phase transformations. Softening/hardening behavior is also reported for the first time in these nanowires under tensile/compressive loadings, which cause asymmetry in their yield strength behavior in the stress-strain space. Result shows that a sharp increase in energy with increasing strain under compressive loading causes hardening of the nanowire, and hence, gives improved yield strength as compared to tensile loading.