Effect of the chromium content on the mechanical properties and microstructural evolution of ion-irradiated Fe-Cr model alloys

Full text of publication follows: Effect on the chromium content on the hardness changes and microstructural evolution in irradiated Fe-Cr model alloys (Fe-5, 9, 12 and 15 wt%) before and after a post-irradiation heat treatment at 673 K or 773 K is investigated using a nano-indentor and transmission electron microscopy (TEM). Ion-irradiation experiments (up to 12 dpa) were preformed with 8 MeV Fe+ ions accelerated at room temperature. TRIM calculation and TEM observation indicated that the depth of maximum displacement damage layer of ion-irradiated regions was about 1.7 μm. nano-indentation with a continuous stiffness measurement (CSM) technique was used to measure a change of the relative hardness of thin ion-irradiated regions. Hardness measurement of the ion-irradiated Fe-Cr alloys before a post-irradiation heat treatment showed that an increase of the hardness by an ion irradiation rises linearly with the chromium content at a low dose level. However, Fe-9wt%Cr showed a reduced irradiation-induced the increase of hardness with the level of a dose. Fine ion-irradiation induced dislocation loops were observed by a weak beam dark field TEM imaging. These fine dislocation loops had Burgers vectors of <001> and 1/2<111>, which were distinguished with actual TEM images. TEM analysis showed that the size of the dislocation loops increased and the population of the dislocation loops with a Burgers vector of <100> increased with the chromium additions. After a post-irradiation heat treatment, the hardness measurement of irradiated Fe-Cr alloys showed that the reduction of the hardness by a heat treatment decreased with the chromium additions. An interesting feature is that as the chromium content is lowered in Fe-Cr model alloys, the size of the ion-irradiation induced dislocation loops increases significantly after a post-irradiation heat treatment, whereas it decreases before a post-irradiation heat treatment. Based on the present experimental results, we discuss in detail the correspondence between the irradiation-induced changes in the hardness and in the microstructure and the role of the chromium atom in Fe during an irradiated microstructural evolution. (authors)