Tuning Phase Transformations in Epsilon-Martensite—Pathways to Extend the Limit of Metastability Engineering

In contrast to pseudo-elastic martensitic phases, typical BCT-martensite formed through plastic straining often exhibits brittle-like features, largely ascribed to the extensive defect density and the pronounced plastic accommodation in the vicinal parent phase. A somewhat intermediate situation occurs when epsilon-martensite is nucleated during plastic deformation: the similar atomic stacking sequence between HCP and FCC lattices enables more moderate interfacial mismatch, alleviating plastic accommodation. In light of this, this presentation focuses on extending the mechanical benefits of metastability by tuning phase transformations in epsilon-martensite. Three strategies will be explored in greater depth: (1) activating a plastic strain-induced FCC-HCP-FCC martensitic transformation chain; (2) applying a displacive reversion treatment coupled with partial recrystallization; and (3) delaying the formation of blocky epsilon-martensite by massive stacking fault nucleation. Finally, a discussion towards the future of metastability engineering will also be included.