Effect of solid solution hardening and stacking fault energy on plastic flow and acoustic emission in Cu–Ge alloys

The acoustic emission (AE) has been investigated systematically in tensile strained model Cu–Ge alloys with germanium concentration varied from 0.1 to 9.0 at.%. The role of various micro-structural factors in AE is discussed and the effects of solid solution hardening and stacking fault energy (SFE) on the AE power spectra are clarified. It is shown that even a small (0.1 at.%) addition of Ge changes AE significantly, whereas the dislocation AE mechanisms are similar in pure copper and its dilute alloys. It is argued that the solution hardening is a main factor governing the AE behaviour in dilute Cu–Ge solutions, resulting in the increase of lattice friction, decrease of dislocation velocity and, consequently, in reduction of the AE energy. The AE technique shows that twinning occurs from the very early stage of plastic deformation together with dislocation slip in copper alloys with germanium content as high as 5.7 at.% and the SFE is of 20 mJ m −2 and lower. Both types of AE sources—dislocation glide and twinning—have distinct features in the AE power spectra and waveforms and are discriminated with a help of data categorization technique and cluster analysis of AE.