*Communication* **Microstructure and Superelastic Properties of FeNiCoAlTi Single Crystals with the <100> Orientation under Tension**

**Li-Wei Tseng 1,\*, Chih-Hsuan Chen 2, Yu-Chih Tzeng 3, Po-Yu Lee 1, Nian-Hu Lu <sup>2</sup> and Yury Chumlyakov <sup>4</sup>**


**Abstract:** The microstructure and superelastic response of an Fe41Ni28Co17Al11.5Ti2.5 (at.%) single crystal along the <100> orientation was investigated under tension at room temperature after aging at 600 ◦C for 24 h. From the superelastic results, the samples aged at 600 ◦C for 24 h exhibited 4.5% recoverable strain at room temperature. The digital image correlation (DIC) method was used to observe the strain distribution during the 6.5% applied strain loading. The DIC results showed that the strain was uniformly distributed during the loading and unloading cycles. Only one martensite variant was observed from the DIC results. This was related to the aging heat treatment times. The martensite morphology became a single variant with a longer aging time. The thermo-magnetization results indicated that the phase transformation and temperature hysteresis was around 36 ◦C. Increasing the magnetic field from 0.05 to 7 Tesla, the transformation temperatures increased. The maximum magnetization was 160 emu/g under the magnetic field of 7 Tesla. From the transmission electron microscopy results, the L12 precipitates were around 10 nm in size, and they were high in Ni content and low in Fe content.

**Keywords:** superelasticity; FeNiCoAlTi; shape memory alloys
