Displacement Damage In Ferritic/Martensitic Steel Induced By Self-ion Irradiation

Material problem is one of the key factors restricting the development of nuclear energy. Structure materials with better irradiation and corrosion resistance are needed to apply in advanced nuclear energy systems(Generation-Ⅳ, fusion reactor and ADS) with intense condition like high temperature, irradiation field and corrosion etc.. Due to its excellent properties like high temperature creep resistance, reduced irradiation swelling rate, high thermal conductivity and low thermal expansion coefficient, ferritic/martensitic(F/M) steel with 9-12%Cr are proposed as one of the most competitive candidate materials for advanced nuclear energy systems. Self-ion irradiation is an effective way to emulate displacement damage akin to the one induced by neutron in structure materials, since it introduces only displacement damage without foreign atoms. The investigation on displacement damage in ferritic/martensitic steel can not only provide important basic data for its application in advanced nuclear energy system, but also possesses a great significance in the research of structure materials’ performance degradation.In this thesis, SIMP and T91 steel are irradiated with 3.25 Me V and 1.625 Me V single energy Fe ion to different fluences at temperatures of room temperature(RT), 300, 450 and 550 ℃. After irradiation, evolutions of vacancy-type defects, dislocation loops and mechanical property of the two steels are investigated by using Doppler Broadening Spectrum of slow Positron Annihilation(DBPAS), Transmission Electron Microscopy(TEM), and Nano-Indentation Teconology(NIT). Besides, a brief evalution on the performance of SIMP is shown in the end.1. The formation and evolution of vacancy-type defects in F/M steels induced by Fe ion irradiation are investigated. It is shown that 3.25 Me V and 1.625 Me V Fe ion irradiation produce a large number of of vacancy-type defects at RT. With the increase of irradiation fluence, the concentration of vacancy-type defects increased in the sample irradiated at RT, whereas for the sample irradiated at 450℃,it first increased and then decreased. At irradiation fluence of 1.7×1016ions/cm2, with the increase of irradiation temperature, the concentration of vacancy-type defects in SIMP steel irradiated by 3.25 Me V Fe ion gradually reduced, whereas for the T91 sample irradiated by 3.25 Me V Fe ion as well as SIMP and T91 sample irradiated by 1.625 Me V Fe ion it first reduced and then increased. In addition, at same irradiation temperature and fluence, Fe ion with low energy can induce more vacancy-type defects in the samples.2. The evolution of dislocation loops induced by 3.25 Me V Fe ion irradiation is studied. It is shown that irradiation introduce amount of dislocation loops in the samples. With the increase of irradiation temperature and fluence, the mean size of dislocation loops increased, and the density of dislocation loops first increased and then decreased.3. Hardening effect induced by Fe ion irradiation is investigated. It is shown that all the samples were hardened after irradiation. At RT and 450℃, as irradiation fluence increase, the increment of hardness first raised and then reduced. At fluence of 1.7×1016ions/cm2, as irradiation temperature increase, the increment of hardness increased first and then decreased.4. In different irradiation conditions, the concentration of vacancy type defects in SIMP steel are close to or lower than that of T91 steel. At higher temperature(1.625 Me V Fe ion: ≥ 300 ℃; 3.25 Me V Fe ion: ≥ 450 ℃) and fluence(1.625 Me V Fe ion: 2.5×1015ions/cm2;3.25 Me V Fe ion:≥1.7×1016ions/cm2), the increment of hardness of SIMP samples are less than that of T91 samples.