| Reactor pressure vessel steel is the first barrier against the radiation release,the excellent mechanical properties of which is important for the operation of the nuclear power plants.However,long-term and high-temperature neutron irradiation will induce the hardening and embrittlement of the steels,reduce the toughness and plasticity of the steel and increase the risk of fracture.Therefore,the systematic and quantitative analysis of irrradiation mechanism is of great significance for the safe operation and life extension of nuclear power plants.The sample used in this study is a Fe-Mn-Si ferrite model alloy designed according to the composition of industrial reactor pressure vessel steel,in which Mn and Si are the main alloying elements.The alloys were irradiated by Fe~+ions at different irradiation temperatures(room temperature,250°C and 350°C)under different irradiation doses(0.1 dpa,0.6 dpa and 1.5 dpa).Nano-indentation test was used to measure the microhardness.The evolution of clusters and the segregation of elements at grain boundaries in Fe-Mn-Si alloys under different irradiation conditions were systematically studied by means of advanced characterization methods such as scanning electron microscope,electron backscattering diffraction and atom probe tomograph,so as to reveal the distribution of alloy elements during irradiation and the contribution of clusters to irradiation hardening.Analysis of the data leads to the following conclusions:Ion irradiation increases the hardness of the Fe-Mn-Si alloy,and the hardening effect becomes more obvious with the increase of irradiation temperature or dose.Ion irradiation leads to the formation of Mn-Si clusters in the Fe-Mn-Si alloy;under the same irradiation temperature,the number density and volume fraction of Mn-Si clusters increase linearly with the increase of irrradiation dose;and the Mn fraction of the clusters increases with the increase of the irradiation temperature;in addition,with the increase of the irradiation temperature and dose,the average size of the clusters is almost unchanged,and most of the clusters are small in size,so the contribution of the Mn-Si clusters to irradiation hardening is not obvious.Ion irradiation has an important effect on the element segregation at grain boundaries.After irradiation,Mn atom diffused from the matrix nearby to the grain boundary,while the impurity C diffused from the grain boundary to the nearby areas;and Mn-rich phase would precipitat at the grain boundary under a higher irradiation dose. |
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