Quantitative Analysis of Grain Boundary Segregation of Boron in Steel with Secondary-Ion Mass Spectrometry in Comparison to Atom Probe Tomography

Abstract To identify the origin of high intensities of BO2− signals on grain boundaries (GBs) in boron (B) mapping using secondary-ion mass spectrometry (SIMS), atom probe tomography analysis was performed on high-brightness GBs in the steel with the addition of B. Homogeneous segregation of B atoms as a solid solution, rather than continuous GB precipitation of fine boride, was observed at the GBs. The amounts of B segregation varied between the GBs. An estimation of the incident angle of the GB from the sample surface in each GB indicated that the high-brightness GBs always have smaller incident angles than the median angle under the assumption of random GB orientation, resulting in an increase in the GB area in the SIMS analyzed region. The product of the actual B segregation amount and area increase factor roughly corresponded to the apparent B intensity of the GB in B-mapping with SIMS. The high brightness in the B-mapping originated mainly from small incident angles of GB from the sample surface in the steel. The incident angle of the GB plane must be considered for quantification of GB segregation of B in the SIMS analysis.