XRD Line Profile Analysis of Ball Milled ODS Ferritic Steel Powder Consolidated by Hot Isostatic Pressing

In this study, an ODS ferritic steel powder of composition Fe–12Cr–2W–1Zr–0.2Y (in wt %) was mechanically alloyed in a planetary ball mill, until the proper solid solution was established and consolidated by hot isostatic pressing. Basic microstructure features, in terms of the nature, density of the dislocations, lattice parameter and lognormal domain sizes distribution,—were determined by X-ray diffraction profile analysis, using the recent, powerful whole powder pattern modelling approach. XRD analysis revealed that microstructure during ball milling evolved towards the nanocrystalline state made of very fine, narrowly dispersed crystallites with strongly correlated dislocation structure of extensive number density of dislocations reaching almost 1017 m–2. Mean coherent domain size was estimated using both whole powder pattern modelling and modified Williamson–Hall methods, which yielded 9.5 and 7.5 nm, respectively. Powder consolidation induced crystallite growth accompanied with restrained drop in dislocation density. The anisotropic strain broadening of bcc iron diffraction peaks was taken into account by incorporating the dislocation contrast factor, directly related to elastic constants of material and to the dislocation slip system.