Study of micro-plastic deformation in pure iron before macro-yielding using acoustic emission, electron backscattered diffraction and transmission electron microscopy

Abstract

Micro-plastic deformation of a DT4 iron ingot with different low angle grain boundary (LAGB) ratios and initial dislocation states (IDS) before macro-yielding was studied with the aid of acoustic emission (AE), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM). The results show that AE only occurs in a reference sample via dislocation multiplication during micro-plastic deformation, while AE occurs in a rolled annealed (RA) sample via dislocation multiplication supplemented by collective motion of local dislocations. The formation of dislocation walls (DWs) and higher LAGB ratios increase the maximum AE energy and amplitude in the RA sample by 476.19% and 22.54% compared to the reference sample, respectively. Higher LAGB ratio (83.181% in the RA sample compared to 9.152% in the reference sample) and initial dislocation density in the RA sample produce earlier dislocation multiplication, resulting in cooperative dislocation motion. Generation of type A2 signals during micro-plastic deformation is dominated by synergistic motion of local dislocations, while dislocation multiplication is secondary. Therefore, LAGB and IDS will change the micro-plastic deformation behavior by influencing dislocation multiplication and changing the dislocation motion mode. The results from this study provide greater understanding of plastic deformation.