Acoustic emission during Lüders-band type martensitic transformation and thermal recovery in Cr20Mn20Fe20Co34.4Ni5.6 high entropy shape memory single crystals

Acoustic emission, AE, during Lüders band type martensitic transformation and during thermal recovery in Cr 20 Mn 20 Fe 20 Co 34.4 Ni 5.6 (at%) high entropy shape memory single crystals are investigated. The stress induced Lüders-band type martensitic transformation was induced by application of uniaxial tensile stress along the [ 1 ̅ 44] direction at room temperature. It is shown that the Lüders-type martensite nucleation and propagation is an intermittent process and results in acoustic emission signals. There is large AE activity at the band localization and it gradually decreases during its propagation, which is also a jerky process. The large acoustic activity at the band localization is due to the presence of nucleation barrier of elastic origin, which is proportional to the Lüders-peak area. Sub-cycles of the propagation stage showed AE activity in accordance with the Kaiser effect. It is concluded, from the local equilibrium model of thermoelastic martensitic transformations, that the martensite formed during stress loading is stabilized by a large dissipative energy. The cumulative elastic energy gradually decreased during thermal recovery indicating that this process has also the intermittent character. Characteristic exponents of the acoustic emission signals obtained during Lüders-type transformation and thermal recovery are the same within the error bars and agree well with data obtained during stress or temperature induced martensitic transformations in Ni 49 Fe 18 Ga 27 Co 6 shape memory single crystals. • Acoustic emission, AE, during Lüders-type martensite nucleation and propagation. • Large AE activity at the band localization, which decreases during propagation. • The martensite is stabilized by the dissipation energy of transformation. • The nucleation barrier for band localization is proportional to the peak area. • Stepwise increase of AE energy is due to relaxation of elastic energy during heating.