Acoustic Emission Responses of Three Typical Metals During Plastic and Creep Deformations

In this paper, the acoustic emission (AE) responses of three typical engineering metals (namely, Q235 carbon steel, H62 brass and 304 stainless steel) during plastic and high-temperature creep deformations were experimentally investigated. To gain insight into the AE response mechanisms, the micro scale mechanical behaviors of these metals were studied with a micro-tensile tester with observation by scanning electron microscopy (SEM). The following observations were found: (1) although the intensities and activities of the AE signals greatly differed under the same configurations, the AE peak values appeared at the transition from elasticity to plasticity for all three metals; (2) compared to the AE signal intensity during plastic deformation, the signal intensity during high-temperature creep was much weaker; (3) slip lines appeared within the crystal grains at the stress level corresponding to the peak AE signal intensity, but the densities of the slip lines and their crossover were not proportional to the AE signals of the metals. From these findings, the following conclusions were drawn about the application of AE: (1) AE is more scientific method to determine the yielding point of a metal without plastic flow than the nominal yield stress; (2) AE can be used to determine the deformation mechanism at high temperature, particularly, to distinguish creep from plastic deformation; (3) the AE response is the result of a sudden energy release by dislocation motion; however, the AE signal intensity is not necessarily proportional to the dislocation activity.