High-Temperature Hardness Anomaly in Ti–Ni–Fe-Based Multiphase Intermetallic

The room temperature (RT) and high-temperature (373–573 K) hardness of individual phases of Ti₄₅Ni₅₀Fe₅ multiphase intermetallic are evaluated using nanoindentation. The B2 matrix exhibits anomalous behavior whose hardness decreases from RT to 373 K followed by an increase up to 573 K. In contrast, the hardness of the DO₂₄ phase continuously reduces up to 473 K. Molecular dynamics simulation of single crystal compression of B2 matrix shows the presence of $\frac{1}{2}⟨\overline{1}11⟩$ screw partial dislocations at all temperatures whose density increases up to 473 K followed by a decrease at 573 K. It is anticipated that individual screw super partial cross-slips from {110} to {211} plane at the higher temperature, with their core becoming nonplanar. The nonplanar core of these screw partials acts as a dragging point for the motion of dislocation leading to hardness anomaly vis-à-vis yield strength anomaly. The DO₂₄ phase does not exhibit any anomalous behavior in hardness in the studied temperature range due to the presence of super partial dislocations bounded by super intrinsic stacking faults instead of antiphase boundaries.