Research progress on resistance to intergranular cracking of molten salt reactor structural materials
Recently, the research team at the Shanghai Institute of Applied Physics(SINAP), Chinese Academy of Sciences, has made significant advancements in enhancing the resistance of molten salt reactor structural materials to Te-induced intergranular cracking. The related findings have been successively published in Corrosion Science (Paper title: "A Study on the Resistance to Tellurium Diffusion of MCrAlY Coating Prepared by Arc Ion Plating on a Ni-16Mo-7Cr Alloy") and Surface & Coatings Technology (Paper title: "A Study on Microstructure Evolution of MCrAlY Coatings After Thermal Aging in Te Environment"). The first author of both papers is Jijin Wu, a Ph.D. student at SINAP, with Prof. Hefei Huang and Prof. Fenfen Han from the Materials Research Department serving as corresponding authors.
GH3535 alloy is employed as a structural material for molten salt reactors (MSRs) due to its excellent resistance to molten salt corrosion, high-temperature mechanical properties, and neutron irradiation resistance. However, during reactor operation, tellurium (Te), a fission product, diffuses from the alloy surface into the GH3535 matrix along grain boundaries, leading to reduced intergranular cohesion and subsequent intergranular cracking, which threaten the long-term safety of the reactor. In this study, a NiCrAlYSi coating was prepared on GH3535 alloy by arc ion plating system to investigate its Te diffusion inhibition capability and microstructural evolution during prolonged exposure to Te vapor. Results demonstrate that the Te diffusion depth in the NiCrAlYSi coating is significantly lower than that in the bare GH3535 alloy. The coating’s ultra-fine-grained structure and high Cr content facilitate the formation of a dense Cr₃Te₄ reaction layer on the surface, effectively suppressing further inward diffusion of Te and thereby enhancing the alloy’s resistance to Te-induced intergranular cracking. During thermal aging, the high Cr content in the coating facilitates the transformation of the reaction product Cr₃Te₄ into Cr₇Te₈, releasing Te atoms into the coating. Concurrently, Yttrium (Y) in the coating captures the inward-diffusing Te to form YTe phases. This work provides a novel approach for improving the Te resistance of MSR structural materials and offers theoretical foundations and data-driven insights for the compositional design and performance optimization of Te-resistant coatings.
This research was supported by the National Natural Science Foundation of China and the Youth Innovation Promotion Association, CAS.
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