Description
Prospective materials for large-scale structural applications, Fe-based shape memory alloys stand out due to their cost-effectiveness and the relatively low temperature dependence of their transformation stress. Coupled in situ investigations were conducted on a Fe-Mn-Al-Ni-Ti single crystal subjected to compression and two Fe-Mn-Al-Ni-Ti oligo-crystals deformed in tension. The superelastic material behaviour was investigated by combining characterization techniques such as digital image correlation, infrared-thermography and acoustic emission. A poor strain reversibility and a premature plastification of the parent phase was observed in case of the single crystal due to an unfavorable crystal orientation. Contradictory transformation behaviours were observed in the two oligo-crystals. One specimen exhibited a promising strain reversibility and characteristic signs of degradation, while the other specimen displayed a poor strain reversibility due to an unusual confinement of the martensitic phase transformation within an unfavorably oriented grain. In the former case, an increase in the dislocation density within five cycles was detected through a shift in the median frequencies of the acoustic signals. In the latter case, a strong coupling between martensite nucleation and dislocation generation led to a pronounced martensite stabilization after a single loading cycle.
