Thermal and acoustic noises generated by austenite/martensite transformation in NiFeGaCo single crystals

Jerky character of austenite/martensite transformation has been investigated in NiFeGaCo shape memory single crystalline samples simultaneously by Differential Scanning Calorimeter, DSC, and by Acoustic-Emission, AE. Statistical analysis of the noise signals resulted in the same energy exponents, ε, about 1.7 ± 0.1 for heating, as well as 2.0 ± 0.1 for cooling, from both acoustic emission and thermal signals at low cooling rates (dT/dt = 0.1 K/min). The exponents of peak amplitudes of AE signals are α = 2.5 ± 0.1 and 2.9 ± 0.1 for heating and cooling, respectively. The obtained exponents fulfill the scaling rule (α−1)/(ε−1) = z with z = 2. Optical observation of the transformation confirmed that it takes place by single interface motion, i.e. the jerky character is the result of the stop-and-go type motion of this interface.