Print Email Facebook Twitter A study of the microstructural stability and defect evolution in an ODS Eurofer steel by means of Electron Microscopy and Positron Annihilation Spectroscopy Title A study of the microstructural stability and defect evolution in an ODS Eurofer steel by means of Electron Microscopy and Positron Annihilation Spectroscopy Author Marques Pereira, V. (TU Delft (OLD) MSE-3; TU Delft Reactor Institute Delft) Schut, H. (TU Delft RST/Neutron and Positron Methods in Materials) Sietsma, J. (TU Delft Materials Science and Engineering; TU Delft (OLD) MSE-3) Department Materials Science and Engineering Date 2020 Abstract An approach to improve the performance of steels for fusion reactors is to reinforce them with oxide nanoparticles. These can hinder dislocation and grain boundary movement and trap radiation-induced defects, thus increasing creep and radiation damage resistance. The present work investigates the thermal stability of the microstructure and the evolution of defects in a 0.3% Y2O3 dispersed Eurofer steel. Samples were annealed for 1 h under vacuum, from 600 K to 1600 K, followed by cooling inside the furnace. Electron Microscopy techniques and Vickers Hardness were used to characterize the microstructure and evaluate its thermal stability. Positron Annihilation Spectroscopy Doppler Broadening (PASDB) was used to monitor the evolution of defects, such as dislocations and vacancies, and their interaction with Y-O based nanoparticles. Several types of events take place simultaneously in the material, due to its initial deformation caused by mechanical alloying, the presence of oxide particles and austenitic phase transformation. Annealing up to 1000 K shows that the Y-O based nanoparticles keep the microstructure refined. Upon cooling from 1200 K (above Ac3), martensite forms with an equiaxed morphology, instead of the conventional lath form, due to the pinning of prior-austenite grain boundaries by the oxide nanoparticles. Annealing at 1400 K and 1600 K results in the progressive coarsening of Y-O based nanoparticles and their loss of ability to pin grain boundaries. PASDB shows that annealing up to 1200 K leads to an overall decrease in defect concentration, mainly due to recovery of dislocations. After annealing at 1400 K and 1600 K, PASDB indicates the formation of a different type of positron trap. The hypothesis is that, at these temperatures, clusters of thermal vacancies are trapped by the oxide nanoparticles, accumulating at their interfaces with the matrix and being retained in the material upon cooling to room temperature. Subject Deformation stateMartensitic ODS steelMechanical alloyingThermal-vacancy clustersY-O based Nanoparticles To reference this document use: http://resolver.tudelft.nl/uuid:89a0d33b-5992-48d3-937a-210923f4edac DOI https://doi.org/10.1016/j.jnucmat.2020.152398 ISSN 0022-3115 Source Journal of Nuclear Materials, 540 Part of collection Institutional Repository Document type journal article Rights © 2020 V. Marques Pereira, H. Schut, J. Sietsma Files PDF 1_s2.0_S0022311520310060_main.pdf 6.07 MB Close viewer /islandora/object/uuid:89a0d33b-5992-48d3-937a-210923f4edac/datastream/OBJ/view