Elucidating the deformation characteristics of Ti–Ni–Fe based pseudo-binary B2 intermetallics

Abstract

The room temperature uniaxial compression behavior of homogenized Ti50Ni50-xFex (5≤x ≤ 45) pseudo-binary B2 intermetallics has been investigated. The compressive stress-strain curves of these intermetallics exhibited three different characteristics (a) intermetallics with low Fe content (i.e., Ti50Ni45Fe5 and Ti50Ni40Fe10): exhibited stress induced martensite (SIM) transformation (B2 → B19 ') (marked by a plateau with non-linear elastic regime) followed by significant plastic deformation up to ∼ 40 % strain marked with significant strain hardening, (b) intermetallics with moderate Fe content (Ti50Ni35Fe15) showed no SIM transformation, but a typical smooth elastic-plastic transition with maximum strain to failure of ⁓ 11–12 % was observed, and (c) intermetallics with high Fe content (≥ 25 at. %) displayed a very small strain to failure (≤ 5 %) without visible plastic deformation. The TEM and XRD analysis of the deformed (15 % and 40 % strain) Ti50Ni45Fe5 and Ti50Ni40Fe10 intermetallics indicated the presence of internally twinned martensite variants (MVs) along with severely dislocated banded B2 matrix. The observed contrast in the deformation characteristics has been attributed to the variation in the values of elastic constants (C' and C44) and Zener anisotropy (A) with Fe content. The SIM transformation in Ti50Ni45Fe5 and Ti50Ni40Fe10 occurred at lower values of C' and C44 (due to elastic softening) and relatively low Zener anisotropy A. The significant plastic strain in these two intermetallics was accommodated by the presence and deformation of super intrinsic stacking faults (SISFs) formed by dissociation of 12⟨111⟩ screw super-partials. In contrast, the deformation in the intermetallics with high Fe content (≥ 25 at. %) was governed by the activation of ⟨100⟩ screw dislocations.