Abstract
An iron-molybdenum alloy powder was extensively deformed by high energy milling, so to refine the bcc iron domain size to nanometer scale (~10 nm) and introduce a strong inhomogeneous strain. Both features contribute to comparable degree to the diffraction peak profile broadening, so that size and strain contributions can be easily separated by exploiting their different dependence on the diffraction angle. To assess the reliability of Line Profile Analysis, results were compared with evidence from other techniques, including scanning and transmission electron microscopy and X-ray small angle scattering. Results confirm the extent of the size broadening effect, whereas molecular dynamics simulations provide insight into the origin of the local atomic, inhomogeneous strain, pointing out the role of dislocations, domain boundaries and interactions among crystalline domains.
Highlights
The material of the present study was selected according to several requirements, and to be representative of a broad class of case studies in chemistry, physics and materials science
High-energy ball-milling of a FeMo powder has been described as a three-stage process[17]: last stage, set in after extensive grinding (> 32 h), yields a homogeneous microstructure made of roughly equiaxed nanocrystalline domains with a high density of dislocations
Even if our Molecular Dynamics (MD) simulations are limited to very short times, and cannot account for diffusion-driven processes, and in general for all what happens on a longer time scale, it is plausible to conclude that the observed microstrain is only partly caused by line defects lying inside the crystalline domains
Summary
The material of the present study was selected according to several requirements, and to be representative of a broad class of case studies in chemistry, physics and materials science. As a direct experimental validation, both features were verified in a recent study, where a ball milled FeMo powder has been measured ten years after grinding[17], providing the same size/strain and unit cell parameters within experimental error, and no measurable signals from oxide phases[16,24].
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