Magnetic force microscopy observation of sensitized Inconel 600

An application of magnetic force microscopes (MFM) is proposed to the characterization of sensitized Inconel 600 alloy with submicron order accuracy. The magnetic microstructures of Inconel 600 sensitized at $\text{620\hspace{0.05em}°}\mathrm{C}$ for various heat treatment periods were observed by means of a MFM. MFM images show semicontinuous morphologies of the magnetizations near and at grain boundaries. The absolute value of the MFM signal, the phase shift between the oscillation of the cantilever and the piezoelectric actuator, at the grain boundary increases at first and then decreases with increasing heat treatment time, while the full width at half maximum about the MFM signals across the grain boundary increases continuously. These results coincide with the fact that the chromium content decreases at first due to production of the chromium carbide and then increase slightly due to the change in the activities of carbon and chromium near the grain boundaries. This method is useful because MFMs enable very high spatial resolution observations with minimal sample preparation and relatively easy operations.