Characteristics of nuclear-grade Ni-Cr-P brazing paste and microstructure and mechanical properties of its brazed joint of stainless steel

Le résumé fourni par la source

With the swift advancement of fourth-generation nuclear reactors and small modular reactors， the operating conditions for nuclear fuel elements， including temperature and irradiation environment， have become increasingly harsh， which in turn places higher demands on the performance of brazing materials. To promote the high-quality and self-sufficient development of nuclear-grade Ni-based brazing paste， a comprehensive and systematic investigation is carried out on the fundamental characteristics of imported nuclear-grade Ni-Cr-P brazing pastes.The findings reveal that the brazing paste contains 12.7 % （mass fraction， the same below）of a binder that decomposes or volatilizes at temperatures below 300 ℃. The residual amounts of nitrogen， oxygen， and sulfur are less than 0.015%， and the residual amount of carbon is less than 0.055%. The filler powders are spherical particles within the mesh size range of 120-230， composed of a Ni3P-type compound and a Ni-based solid solution. The filler composition is Ni-13Cr-10.5P， and it has a hardness of（626±23）HV0.3.When using this paste to braze nuclear-grade 304L stainless steel， the joints mainly consist of a Fe-Ni-Cr solid solution and a Ni₂P-type compound. At room temperature， the joints demonstrate a tensile shear strength of（226±14） MPa and a compressive shear strength of（184±10） MPa. However， the tensile shear strength drops to （130±5） MPa at 350 ℃. All fractures occur within the seam area and exhibit a brittle fracture mode. Under a stress ratio of 0.1 and a stress amplitude of 0.45Fmax， the joint shows a fatigue life exceeding 10⁶ cycles.

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