Nondestructive characterization of stress state changes induced by electromagnetic shocking treatment

The stress state of metals can be tailored by the electromagnetic shocking treatment (EST), which is mainly characterized by destructive method. This work aims to propose a nondestructive method to characterize the stress state changes induced by EST effectively. The coercivity shows nonlinear responses under increasing current density (40 A/mm²–71 A/mm²), in which the coercivity has decreased significantly under the current density of 47.5–62.5 A/mm². Multi-scale stress characterization is utilized at the effective EST parameter, the X-ray diffraction (XRD) results show that dislocation density decreases by 35.2 % and the residual stress decreases by 35.9 %, revealing that the residual stress has been released after EST. The quasi-in-situ electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) results indicate that local stress has been released and homogenized as well. The characterization of magnetic domain suggests that the pinning effect of stress on domain walls (DWs) will decrease as the stress concentration is decreased and homogenized, which facilitates the reverse magnetization and decreases coercivity. A mathematical model among coercivity, stress and current density has been established to characterize the stress state under EST. This study demonstrates the significant potential of coercivity measurement in further quantitatively characterizing the stress state, especially under the applications of EST.