Transition from many domain to single domain martensite morphology in small-scale shape memory alloys

Superelasticity and Tunable Thermal Expansion across a Wide Temperature Range

“…This intrinsic character is crucial for the thermal-induced shape memory (SM) effect, making its operation both T-sensitive and reliable [5][6][7] . Some applications [8][9][10][11] , such as in-depth space exploration require stable SM materials that function across a wide T-range of hundreds Kelvin. However, all current SM alloys (SMAs) exhibit the stress-induced superelasticity (SE) within only a narrow T-range (tens of Kelvin) and with a large hysteresis [8,12] .…”

A coupled kinetic Monte Carlo–finite element mesoscale model for thermoelastic martensitic phase transformations in shape memory alloys

“…The corner regions partially transformed at higher strains (e.g., ε = 0.04-0.052), and retained some austenite until very high applied strains. The transformation behavior near the corner regions resembles that in oligocrystalline SMA wires with a bamboo grain structure [72]; the buffer layers in the present simulations may play a similar role as unfavorably oriented grains that do not transform within the range of applied load. In other regions, new martensite plates formed at relatively low strains and grew and impinged at higher strains.…”

Surface roughness-controlled superelastic hysteresis in shape memory microwires

“…Lastly, previous studies have shown that smaller wires in this size range exhibit larger hysteresis than larger wires [3]. In a previous paper we ascribed this size effect to the increased sampling of obstacles at the wire surface by the austenite/martensite interface [2]. Thus, it is especially suggestive that although the diameter of the polished wire in Fig.…”

“…Fine wires of Cu-based shape memory alloys (SMAs) with bamboo grain structure are interesting because they exhibit single crystal-like behavior without the restrictions in size and cost that come with single crystal production [1]. Recent interest in these structures, which typically have diameters below ∼100 µm, has revealed several size effects upon the martensitic transformation, such as a transition from multi-domain to single-domain martensite morphology [2] and an increased hysteresis size in smaller wires [3]. These effects have been ascribed to two related phenomena.…”