The sound of metal: Acoustic Emission during the deformation of commercially pure titanium

Abstract

Acoustic emission (AE) was monitored in situ during in-plane tensile deformation of a commercially pure titanium plate. Different load orientations were considered: parallel to the rolling direction (RD), transversal direction (TD) and under an angle of 45 degrees (45D) with RD. The AE event rate, peak amplitude, signal duration, rise time and ring-down counts were monitored during deformation. Orientation dependent mechanical behavior, AE signal characteristics and microstructural evolution was observed and correlated to the difference in texture and twinning phenomena. The intensity and characteristics of AE signals in RD and 45D do not change considerably during deformation, which was attributed to the continuous nucleation and growth of compression twins. Anomalous AE behavior in TD was observed, showing two distinct peaks. All signal parameters show significantly decreased values during a first peak, which was correlated to massive nucleation of small tensile twins. These tensile twins disappear with increasing strain, indicating the end of the first peak. The second peak is comparable to the plateau behavior in RD and 45D and occurs during necking. Compression twinning is dominant, but limited to the necking zone. An unfavorable textural effect in TD has been identified, which hinders the formation of compression twins during the homogeneous deformation, as opposed to RD and 45D, resulting in anomalous AE behavior. The acoustic emission technique proves to be a complementary technique to electron diffraction as it allows monitoring and identifying the twinning modes of commercially pure titanium in situ.status: Published onlin