Shape memory alloys (SMAs), especially iron-based SMAs, gained a lot attention in the last years, because of their functional material properties and their low costs in comparison to conventional well- researched NiTi alloys. Whereas NiTi SMAs are mainly used in the medical sector as well as aerospace, iron-based-SMAs may widen the field of application [1-3]. Thus, the construction and automotive sector could come into focus of research. This is due to the lower costs for alloying elements and the fact that these alloys can be processed via established process routes for steel. Although some iron based SMAs show some limitations like a low cyclic stability and low transformation temperatures without external stress, the limitations can be overcome varying the chemical composition, such as the addition of Titan and/or Boron. Tanaka et al. showed with a FeNiCoAlTaB alloy auspicious superelastic properties with a reversible strain of up to 13% [4].

Therefore, the focus in the current study lays on the evaluation of the influence of different heat treatments on the thermo-mechanical properties of a FeNiCoAlTi single crystal. The goal was to identify heat treatment windows in which the alloy shows the highest reversibility during a cooling-heating cycle between -170°C and +80°C. Besides thermo-mechanical testing, transmission electron microscopy was used to characterize the evolution of y'-precipitates and identify the interrelationship between the thermo-mechanical functional material properties, heat treatments and the size and morphology of the y'-precipitates.

References
[1] M. Es-Souni Springer Link, 2005, 381, 557-567.
[2] G. Constanza Materials, 2020, 13, 1856.
[3] A. Cladera Elsevier, 2014, 63, 281-293.
[4] Y. Tanaka Science, 2010, 327, 1488-1490.