On the applicability of the x-ray diffraction line profile analysis in extracting grain size and microstrain in nanocrystalline materials

Measurements of x-ray diffraction (XRD) profiles have been performed on commercially pure Fe and Al powders, cryomilled Fe-3 wt. % Al powders, cold pressed (CP) pure Fe and Al, hot pressed (HP) and hot isostatically pressed (HIP) Fe-3 wt. % Al. Scherrer equation (SE), integral breadth analysis (IBA), and single-line approximation (SLA) methods have been employed to extract grain size and microstrain. The results demonstrate that, in the case of the cryomilled nanocrystalline Fe-3 wt. % Al powders, all these XRD techniques yielded reasonable, consistent grain size results. However, discrepancies were found in cold pressed (CP-Fe), hot pressed (HP-Fe-3 wt. % Al), and hot isostatically pressed (HIP-Fe-3 wt.% Al) samples. TEM imaging revealed the presence of a certain density of dislocations inside the grains in the HP-Fe-3 wt. % Al and HIP-Fe-3 wt. % Al, which is thought to be partly or fully responsible for the observed discrepancies.