On ball-milled ODS ferritic steel recrystallization: From as-milled powder particles to consolidated state
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Recrystallization of a ball-milled ferritic ODS steel is studied towards its evolution from as-milled powder to consolidated state. This characterization has been made possible by using a combination of X-ray Diffraction (XRD) and an innovative method based on an Automated Crystallographic Orientation Mapping (ACOM) tool attached to a Transmission Electron Microscope (TEM). Focus Ion Beam preparation has been essential to obtain a thin section of the ODS steel powder particle and perform the ACOM-TEM study. Relevant temperatures regarding recovery and recrystallization during the heat treatment had first been identified with XRD profile analysis. Selected states were further characterized using ACOM-TEM that provides key information on microstructure, i.e. grain size and morphology, crystallite size, local texture and distortion. ACOM-TEM cartographies have revealed for the first time that the microstructure of as-milled ODS ferritic steel particles consists in very anisotropic grains containing undistorted domains and dislocation walls. This is in agreement with the nanosized crystallites measured by XRD results. The mutual benefits of XRD and ACOM-TEM methods to analyse and describe the microstructure are discussed as well as the reliability of dislocation density measurements provided by ACOM-TEM misorientation measurements. In addition, of the ACOM-TEM results, the microstructural evolution during the processing route is interpreted in terms of a competition between recovery, recrystallization, grain growth and precipitation.
KeywordsDislocation Density Powder Particle Consolidate State Consolidate Sample Local Misorientation
This work was supported by the joint program “CPR ODISSEE” funded by AREVA, CEA, CNRS, EDF and Mécachrome under contract no 070551. It was carried out with the support of the Karlsruhe Nano Micro Facility (KNMF, http://www.kit.edu/knmf), a Helmholtz Research Infrastructure at Karlsruhe Institute of Technology (KIT, http://www.kit.edu). Authors also gratefully acknowledge Muriel Véron and Edgar Rauch for their support in ACOM-TEM data interpretation.
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