Residual stress- and microstructure anisotropies in laser-hardened or shot peened surface

Nondestructive testing of laser hardened and shot peened surfaces has been performed by magnetic Barkhausen noise measurements. Derived micromagnetic parameters such as the maximum amplitude of the rectified Barkhausen noise signal M max and the coercivity value H CM corresponding to the position of M max as a function of applied magnetic field strength are found to be sensitive to microstructure and stress anisotropies in subsurface zones. The microstructure profile produced by laser or shot peening treatment and the homogeneity of the shot peened surface evaluated nondestructively. In both the cases, quantitative estimation of residual stresses has been made using x-ray measurements as calibration. The analysis of the microstructure and residual stress in subsurface zones using micromagnetic parameters can be performed by the 3MA testing unit, developed by the Institute for Nondestructive Testing.