Subjects: Physics >> Nuclear Physics Subjects: Nuclear Science and Technology >> Engineering Technology of Nuclear Fusion submitted time 2024-02-27
Abstract： The helium bubbles induced by 14 MeV neutron irradiation can cause intergranular fractures in reduced activation ferritic martensitic (RAFM) steel, which is a candidate structural material for fusion reactors. In order to elucidate the susceptibility of different grain boundaries (GBs) to helium-induced embrittlement, the tensile fracture processes of 10 types of GBs with and without helium bubbles in body-centered cubic (bcc) iron at the relevant service temperature of 600 K were investigated via molecular dynamics methods. The results indicate that in the absence of helium bubbles, the GBs studied here can be classified into two distinct categories: brittle GBs and ductile GBs. The atomic scale analysis shows that the plastic deformation of ductile GB at high temperatures originates from complex plastic deformation mechanisms, including the Bain/Burgers path phase transition and deformation twinning, in which the Bain path phase transition is the most dominant plastic deformation mechanism. However, the presence of helium bubbles severely inhibits the plastic deformation channels of the GBs, resulting in a significant decrease in elongation at fractures. For bubble-decorated GBs, the ultimate tensile strength increases with the increase of the misorientation angle. Interestingly, the coherent twin boundary Ʃ3{112} was found to maintain relatively high fracture strength and maximum failure strain under the influence of helium bubbles.
Subjects: Nuclear Science and Technology >> Other Disciplines of Nuclear Science Subjects: Physics >> Nuclear Physics submitted time 2024-02-28
Lei Peng
Shangming Chen
Jingyi Shi
Yongjie Sun
Yifei Liu
Yinzhong Shen
Hongya He
Huijuan Wang
Jie Tian
Abstract： Ferritic/martensitic (F/M) steel is widely used as a structural material in thermal and nuclear power plants. However, it is susceptible to intergranular damage, which is a critical issue, under service conditions. In this study, to improve the resistance to intergranular damage of F/M steel, a thermomechanical process (TMP) was employed to achieve a grain boundary engineering (GBE) microstructure in F/M steel P92. The TMP, including cold-rolling thickness reduction of 6%, 9%, and 12%, followed by austenitization at 1323 K for 40 min and tempering at 1053 K for 45 min, was applied to the as-received (AR) P92 steel. The prior austenite grain (PAG) size, prior austenite grain boundary character distribution (GBCD), and connectivity of prior austenite grain boundaries (PAGBs) were investigated. Compared to the AR specimen, the PAG size did not change significantly. The fraction of coincident site lattice boundaries (CSLBs, 3 ≤ Σ ≤ 29) and Σ3n boundaries along PAGBs decreased with increasing reduction ratio because the recrystallization fraction increased with increasing reduction ratio. The PAGB connectivity of the 6% deformed specimen slightly deteriorated compared with that of the AR specimen. Moreover, potentiodynamic polarization studies revealed that the intergranular damage resistance of the studied steel could be improved by increasing the fraction of CSLBs along the PAGBs, indicating that the TMP, which involves low deformation, could enhance the intergranular damage resistance.
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