Recently developed iron-based shape memory alloys, i.e. Fe-Ni-Co-Al-X (Ti, Ta, Nb) and Fe-Mn-Al-Ni-X (Ti, Cr), attracted considerable attention due to their unique material properties. Especially, relatively low alloying costs and high reversible transformation strains make them promising candidates for damping applications. One of the key features of the Fe-Mn-Al-Ni shape memory alloy system is its low temperature dependency of the critical stress for martensitic transformation over a wide temperature range, due to its low Clausius Clapeyron slope based on a low transformation entropy change between the bcc parent phase and the fcc martensitic phase. The proposed application temperature range of the alloy is between -196°C and about 150°C. However, no pseudoelastic stress-strain curves at elevated temperatures have been shown in open literature, yet. Moreover, it was shown that formation of nano-sized precipitates, which have a strong impact on the pseudoelastic behavior, already can be observed at room temperature.
The current study focuses on the pseudoelastic behavior of Fe-Mn-Al-Ni at elevated temperatures. Therefore, samples were subjected to a cyclic heat treatment between 1225°C and 900°C in order to initiate abnormal grain growth. Afterwards, different aging treatments were conducted and samples were mechanically tested at temperatures above 100°C. Moreover, hardness measurements were carried out for Fe-Mn-Al-Ni, Fe-Mn-Al-Ni-Cr and Fe-Mn-Al-Ni-Ti in order to determine the impact of different chemical compositions on the aging and precipitation behavior in this alloy system. Based on data obtained it is possible to reveal the suitability of the Fe-Mn-Al-Ni shape memory alloy system for applications at elevated temperatures.