Acoustic emission study of the kinetics of kink bands in the LPSO structure

Abstract

Modern magnesium alloys with the so-called long-period stacking ordered (LPSO) structure possess not only a unique microstructure, but also an excellent set of functional properties (strength, ductility, fatigue and corrosion resistance, thermal stability) that are directly or indirectly associated with the effect of the LPSO phase. In particular, the features of the nano-composite ordering of the LPSO structure govern virtually all aspects of the mechanical behaviour of advanced alloys with such a particular structure. A characteristic feature of their plastic deformation is widely known as the formation of deformation kink bands, the behaviour of which both individually and in the interaction with each other and with lattice dislocations is not well understood. In the present work, it is proposed to use the method of acoustic emission (AE) to study these processes in real-time. The AE method revealed the presence of three simultaneously existing accommodation deformation mechanisms in model Mg-Y-Zn directly solidified crystals with LPSO structure — namely, basic dislocation slip, nucleation and growth of fault bands. Each of these processes generates a specific AE, the features of which are revealed using the original method of statistical cluster analysis of events by their power spectral density function. The growth of deformation kink bands, in contrast to the growth of twins, appears as a large-scale process of defect motion, accompanied by a reorientation of the crystal with the corresponding specific AE and activation of new channels for the basal dislocation slip, which, in the end, enables high plastic properties of the modern alloys with the LPSO structure.