Ultrahigh tensile transformation strains in new Ni50.5Ti36.2Hf13.3 shape memory alloy

Abstract

We report on unprecedented transformation strains exceeding 20% in tension for Ni 50.5 Ti 36.2 Hf 13.3 shape memory alloy (SMA). The strain measurements were made at multiscales utilizing advanced digital image correlation. The display of excellent strain reversibility in shape memory (isothermal deformation between M f and A f ), isobaric thermal cycling (between M f and A f ), and superelasticity experiments (deformation above A f ) confirm a wide range of functionality. The ultrahigh strains in [111] orientation exceed the lattice deformation theory predictions possibly pointing to contributions from mechanical twinning effects. The high strength levels and large strains result in very high work outputs compared to other SMAs.

Laser welding of Cu-Al-Be shape memory alloys: Microstructure and mechanical properties

“…This means that the transformation strain of the welded joints (the length of the superelastic plateau) is of nearly 35%. Such high transformation strains were also reported in Cu-based alloys [33], but also in the Ni-Ti-Hf system [34]. After the end of the superelastic plateau (corresponding to the applied strain of 47.5%) an increasing stress is required to proceed with deformation, where detwinned martensite is first elastically deformed and, subsequently, plastic deformation occurs [35].…”

Shape memory strains and temperatures in the extreme

“…We note that such a high transformation strain level can open new applications. Other experiments on the same alloy were conducted at higher temperatures (50°C) with pure SE response and at low temperatures (À35°C) with pure SME response [78]. The recoverable strains are in agreement with the values presented in Fig.…”

“…Upon heating, the specimen reverts to austenite beginning at austenite start temperatures with 5. The stress-strain response of NiTi13Hf demonstrating strains above 8% with stress levels near 1500 MPa (see also [78]). Fig.…”

“…The stress-strain response of NiTi13Hf demonstrating recoverable strains near 18% which is remarkably high (based on[78]). …”

A revisit to atomistic rationale for slip in shape memory alloys

“…Specifically, the possibility of widespread thermal activation of dislocations pose a critical design constraint in the hot section components [17][18][19], for example. From fabrication standpoint, it is desirable to have very high slip resistance both in austenitic and martensitic crystals in addition to low transformation or twinning stresses, and high recoverable strain [20][21][22]. To that end, developing predictive abilities for assessing the inherent slip propensity in SMA phases would be particularly worthwhile.…”