Study Of Intergranular Embrittlement Micro-mechanism Of Te In Nickle

Molten-salt reactor(MSR) is the ideal reactor to realize the breedber of U233 by using thorium-uranium fuel cycle, and has incomparable advantages: fission fuel sustainable utilization, excellent heat transfer characteristics, inherent safety, producing less long-lived wastes, and so on. As the structural material used in MSR, Hastelloy N alloy has intergranular embrittlement caused by the corrosion of fission product Te in the fuel salts, and its service life will be seriously affected. To deeply understand the Te-induced intergranular embrittlement and failure behavior of Ni-based alloy served as structural materials in MSR, and develop reasonable method to increases the resistance of intergranular embrittlement, it is necessary to study the mechanism of Te-induced intergranular embrittlement of Ni-based alloy in detail.In this study, a thin Te film was uniformly electroplated onto the surface of pure nickel, and then annealed at high temperature to simulate the corrosion behavior of Ni substrate by Te in MSR. The research is mainly concerned with the composition and structure of tellurium corrosion products in nickel crystal and grain boundaries investigated by advanced synchrotron radiation characterization techniques and conventional methods such as focused ion beam(FIB), electron probe(EPMA), XRD, SEM, etc. The corrosion process and embrittlement mechanism of Te in nickel were discussed. The main results could be described as follows.Under 1000?C, lattice diffusion of Te atoms into Ni substrate is predominant. The lattice corrosion products and the grain boundary(GB) corrosion products are both substitutional Ni-Te solid solution without any Te-Te bond came from Te clusters or Ni-Te compounds, which is directly comfirmed on the local atomic scale by Extended X-ray absorption fine structure(EXAFS) techniques. Ni-Te solid solution in the GB region could weaken the GB cohesion and lead to the intergranular embrittlement of Ni-based alloy.The energy of the Ni supercell with different aggregation patterns of Te atoms in Ni lattice was study by first-principles density functional theory(DFT) calculations. The results indicate that the nearest neighbor Te–Te bond is energetically prohibitive in Ni lattice, while Te-Te coordination in the 2nd to 4th shell is possible.A micro-size sample was cut from the GB corrosion area of the 900?C Te-corroded sample through focused ion beam(FIB) techniques, and analyzed by combined Micro-beam X-ray Fluorescence(μ-XRF), Micro-beam X-ray diffraction(μ-XRF), Micro-beam X-ray absorption near edge structure(μ-XANES) to obtained the distribution of Te concentration and composition structure over the GB corrosion area. It was found that the GB corrosion products of different Te concentrations were different.