Examining the Correlation Between Microstructure and Barkhausen Noise Activity for Ferromagnetic Materials

Barkhausen noise emissions occur in ferromagnetic materials on application of an externally varying magnetic field. These emissions primarily occur due to the presence of pinning sites or discontinuities within a material which act as inhibitors to domain wall motion. Overall, Barkhausen noise emissions can capture variations in microstructure, chemical composition, lattice strain, and grain size, and can detect the presence of residual stresses in materials. In this paper, the Barkhausen noise response for a Jominy end-quench test steel sample is examined. Microstructural variations in the form of constituent phases, such as martensite, bainite, pearlite, or ferrite, can be detected via changes in Barkhausen noise signatures. Through Barkhausen noise measurements, it is observed that characteristic peaks corresponding to different phases appear in the spectrum. The characteristic peaks become distinct when the contribution to Barkhausen noise from individual phases becomes significant. This analysis method may be further used to monitor microstructural evolution, and thus understand the contributions of constituent phases to material properties. The technique may be used as a potential tool for the nondestructive evaluation of ferromagnetic materials employed in industrial applications.