Superelasticity and acoustic emission of Ni₄₆Mn₂₈Ga₂₀Co₃Cu₃ microwire

Noise is a common occurrence in many structural and functional materials during plastic deformation processes. The acoustic signal is hard to obtain for traditional materials due to the one-off nature of the deformation. But for shape memory alloys, this phenomenon can be analyzed systematically during cyclic tensile experiments, owing to the shape memory effect. Acoustic emission (AE) is studied in Ni₄₆Mn₂₈Ga₂₀Co₃Cu₃ shape memory microwires with various diameters during stress-induced martensitic transformation. The microwires exhibit fully reversible strain larger than 10% and obvious serration behavior at room temperature. The AE waves obtained during tensile processing reflect the phonon softening and lattice vibration during stress-induced phase transformation. Analysis of the spectra shows that AE frequency concentrates in certain selected frequency ranges, and this result reveals the characteristic nature of collective atom movement. The correlations between the amplitude, cut-off frequency and size effect of the microwires were also analyzed, respectively. Focusing on the relationship between the acoustic properties and deformation behavior of shape memory alloys may provide a new perspective for materials science. (paper)