000213245 001__ 213245
000213245 005__ 20180501110043.0
000213245 0247_ $$2doi$$a10.5075/epfl-thesis-6824
000213245 02470 $$2urn$$aurn:nbn:ch:bel-epfl-thesis6824-1
000213245 02471 $$2nebis$$a10540157
000213245 037__ $$aTHESIS_LIB 000213245 041__$$aeng
000213245 088__ $$a6824 000213245 245__$$aEmbrittlement induced by the synergistic effects of radiation damage and helium in structural steels
000213245 269__ $$a2015 000213245 260__$$aLausanne$$bEPFL$$c2015
000213245 300__ $$a130 000213245 336__$$aTheses
000213245 502__ $$aProf. Anna Fontcuberta i Morral (présidente) ; Dr Philippe Spätig, Dr Yong Dai (directeurs) ; Dr Aïcha Hessler-Wyser, Dr Jean Henry, Dr Maximo Victoria (rapporteurs) 000213245 520__$$aFerritic/martensitic steels are candidate materials for fusion reactor structural components, liquid metal containers of spallation neutron sources, and accelerator driven systems, with good radiation resistance and thermo-mechanical properties. However, embrittlement resulting from the combined effects of radiation induced displacement damage (measured in dpa = displacement per atom) and transmutation products, especially helium gas, is one of the key issues. Four different steels were selected for mechanical and microstructural studies to understand the mechanisms of embrittlement induced by the combined effects of displacement damage and helium after irradiation in SINQ, the Swiss spallation source. The irradiations conditions were in the range: 10.7 ¿ 20.4 dpa with 850-1750 appm He at 160-300 °C. The evolution of the mechanical properties after irradiation was investigated by tensile and hardness tests. Radiation-induced defect clusters and helium bubbles were quantified by transmission electron microscopy (TEM). Emphasis was put on the deformation mechanisms under the different observed fracture mode, (ductile, quasi-cleavage and intergranular), whose occurrence depends on the irradiation conditions (dpa, He content and irradiation temperature). The tensile stress-strain curves and the scanning electron microscopy images of fracture surfaces showed distinct fracture mechanisms under different irradiation and test conditions. The tensile tests showed a yielding stress increase and loss of ductility of irradiated specimens. Hardness was measured on the specimens before tensile testing. The hardness results demonstrated an increasing trend with irradiation dose and helium content. TEM observations were done for all irradiated fractured specimens. Small defect clusters were observed in the 12.3 dpa specimen, but large defect clusters with loop-shape were very few. In the specimens of 17.2, 17.7 and 20.4 dpa, many large dislocation loops were detected besides small clusters. In addition, helium bubbles were observed in all specimens. The average size of defect clusters increased from 4.2 nm to 11.8 nm with dose increasing from 12.3 dpa to 20.4 dpa, whereas the number density did not change significantly. Meanwhile, the average size of visible helium bubbles increased from 1.03 nm to 1.93 nm. The microstructures in deformed area of irradiated specimens were observed and defect free channels with {110} and {112} slip planes were found in some specimens, indicating plastic flow localization. The average width of the channels is about 100 nm.  Regarding the brittle samples, the TEM-lamella were extracted directly below intergranular fracture surfaces or cleavage surfaces by focused ion beam. Strikingly, deformation twinning was observed as the main feature in three irradiated specimens at high dose. Only twins with {112} planes were observed in all of these samples. The average thickness of twins is about 34 nm. Twins started from a fracture surface became gradually thinner with distance away from the fracture surface and stopped in the matrix finally. Features such as twin-precipitates interaction, twin-grain boundary and/or lath boundary interaction were observed. Twinning bands were seen to be arrested by grain boundaries or large precipitates, but could penetrate martensitic lath boundaries. Unlike the case of defect free channels, inside twins small defect-clusters, dislocation loops and dense small helium bubbles were observed.
000213245 6531_ $$aferritic/martensitic steel 000213245 6531_$$airradiation
000213245 6531_ $$adefect clusters 000213245 6531_$$ahelium bubbles
000213245 6531_ $$aTEM 000213245 6531_$$aembrittlement
000213245 6531_ $$amicro-crack 000213245 6531_$$adeformation mechanism
000213245 6531_ $$adefect-free channeling 000213245 6531_$$adeformation twinning
000213245 700__ $$0(EPFLAUTH)210557$$aWang, Kun$$g210557 000213245 720_2$$0240522$$aSpätig, Philippe$$edir.$$g106982 000213245 720_2$$0(EPFLAUTH)104855$$aDai, Yong$$edir.$$g104855 000213245 8564_$$s18494280$$uhttps://infoscience.epfl.ch/record/213245/files/EPFL_TH6824.pdf$$yn/a$$zn/a 000213245 909C0$$0252305$$pLRS$$xU10135
000213245 909CO $$ooai:infoscience.tind.io:213245$$pSB$$pthesis-bn2018$$pDOI2$$pDOI$$pthesis
000213245 917Z8 $$x108898 000213245 917Z8$$x108898
000213245 917Z8 $$x108898 000213245 918__$$aSB$$cIPEP$$dEDMX
000213245 919__ $$aLRS 000213245 920__$$a2015-10-26$$b2015 000213245 970__$$a6824/THESES
000213245 973__ $$aEPFL$$sPUBLISHED
000213245 980__ aTHESIS