Neutron irradiation induced defects and clustering in NF616 and T91

NF616 is a third-generation ferritic martensitic steel, developed to have better creep resistance than the prior generation T91. Unlike relatively numerous studies of T91, there is a lack of understanding of the irradiation effect on the microstructural evolution and mechanical response of NF616. This work evaluated the microstructures and radiation hardening of NF616 irradiated up to 8.2 displacement per atom (dpa) at 292 degrees C-431 degrees C, compared with T91 from two heats. Dislocation loops were observed in all investigated samples. NF616 exhibited comparable loop size but slightly lower loop density than those in the general T91 heat at 430 degrees C. Cavities were only observed in NF616 at 431 degrees C but absent at lower irradiation temperatures (292 degrees C and 359 degrees C). Ni-rich clusters were also observed in NF616 at 431 degrees C, while only weak Ni-clustering were observed at lower irradiation temperatures. Compared to the general T91 heat, NF616 demonstrated better swelling resistance (e.g., one third of swelling in the general T91 heat at 430 degrees C), a slightly higher number density of Ni-rich clusters, and slightly lower radiation hardening. The low-carbon T91 showed the greatest hardening with the largest swelling and loop sizes, despite its lowest irradiation temperature and intermediate dose. The calculated hardening from loops, cavities and Ni-rich clusters using the classic dispersed barrier-hardening model had reasonable agreement with the experiment-derived results, with the primary hardening contribution attributed to dislocation loops. (c) 2021 Elsevier B.V. All rights reserved.

Automated summary

The study found that NF616 exhibits better swelling resistance and slightly higher number density of Ni-rich clusters under high-temperature irradiation conditions, while showing slightly lower radiation hardening. Compared to general T91, NF616 demonstrates better performance at 430 degrees Celsius.