2.3. Optical Microscopy and Electron Backscatter Diffraction

In order to observe the microstructure, the samples were cross-sectioned, mounted in cold mounting resin, ground with a series of SiC papers down to a grid 2400, and then further polished using aluminum oxides with grain size down to 0.05 μm and the 0.04 μm silica oxide, and, finally, argon ion beam cleaned using an IM4000Plus instrument (by Hitachi High-Tech Corporation, Tokyo, Japan). An optical microscopy Axio Imager M1m (by ZEISS, Oberkohen, Germany) and a Nova NanoSEM 450 Scanning Electron Microscopy (SEM) (by FEI Co, Hillsboro, OR, USA) were used. To reveal the possible presence of iron on the surface of the samples, the SEM-EDS (Energy Dispersive Spectroscopy) analysis using S-3500N microscope (by Hitachi High-Tech Corporation, Tokyo, Japan) with the analyzer NORAN 986B-1SPS (by Thermo Fisher Scientific, Waltham, MA, USA) was performed prior and after SMAT.