Speaker
Nerea Ordas
(Materials and Manufacturing)
Description
Oxide dispersion strengthened ferritic steels (ODS FS) are candidate structural materials for future fusion reactors thanks to their high temperature strength, high creep resistance, and good resistance to neutron radiation. Their outstanding behavior is a direct consequence of their extremely fine microstructure and the presence of highly stable and finely distributed nanometric oxide precipitates.
The conventional processing route of ODS FS includes mechanical alloying (MA) of elemental or gas atomized prealloyed powders with Y2O3 particles followed by consolidation by hot isostatic pressing (HIP) or hot extrusion, and finishes with thermo-mechanical treatments to obtain fine grain structures with very fine Y-Ti-O nanoclusters dispersion. However, MA involves several drawbacks like contamination from grinding media, and batch to batch heterogeneities. To avoid MA, a new route called STARS (Surface Treatments of gas Atomized powder followed by Reactive Synthesis) has been developed and is the core of the present work. This route is inspired in the GARS method (Gas Atomization Reactive Synthesis) developed by I.E. Anderson in AMES laboratory.
FS powders already containing the oxide-dispersion formers (Fe-14Cr-2W-(0.3-0.56)Ti-(0.18-0.37)Y) were obtained by gas atomization. Then, a metastable oxide layer was formed on the surface of powder particles. When HIPped at elevated temperatures (>1220°C), this oxide layer dissociates and Y-Ti-O nano-oxides precipitate in the ferritic matrix, as observed by TEM and XAS (X-ray Absortion Spectroscopy). Post-HIP heat treatments at elevated temperatures dissolved the remaining oxides located at prior particle boundaries. However, they can be detrimental from the microstructural point of view as they favour thermally induced porosity and coalescence of residual carbonitrides. Subsequently, hot rolling was performed at 1050 °C. Finally, heat treatments at different temperatures were performed on hot rolled material to remove residual stresses and promote recrystallization.
This work concludes that the STARS route has great potential to obtain ODS Ferritic Steels.
Co-authors
Andris Anspoks
(Institute of Solid State Physics, University of Latvia, Riga, Latvia)
Carmen Garcia-Rosales
(Materials and Manufacturing, Ceit-IK4, San Sebastian, Spain)
Emma Gil
(Materials and Manufacturing, Ceit-IK4, San Sebastian, Spain)
Inigo Iturriza
(Materials and Manufacturing, Ceit-IK4, San Sebastian, Spain)
Jan Hoffmann
(Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen, Germany)
Juris Purans
(Institute of Solid State Physics, University of Latvia, Riga, Latvia)
Michael Rieth
(Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen, Germany)
Nerea Ordas
(Materials and Manufacturing, Ceit-IK4, San Sebastian, Spain)
Teresa Leguey
(Department of Physics, University Carlos III Madrid, Leganes, Spain)
Vanessa de Castro
(Department of Physics, University Carlos III Madrid, Leganes, Spain)