控制晶界特征分布提高Alloy-N合金抗Te致晶界脆性开裂性能的研究

Molten salt reactors have been included as one of six advanced Generation IV reactor types. The Alloy-N (16Mo-7Cr-5Fe-Ni) is used as the structure material for containing and transporting the high temperature molten fluoride salts which have nuclear fuel inside. One of the most serious problems for Alloy-N is the intergranular embrittlement induced by inward diffusion of tellurium which is a fission product. The proposed project plans to investigate the grain boundary engineering (GBE) technique for Alloy-N. The thermal-mechanical processing of GBE and the involved mechanism for enhancing the proportion of low ∑CSL (coincidence site lattice) grain boundary will be focused on. The effect of the grain boundary structure on the diffusion of tellurium along grain boundaries will be investigated with the help of electron probe microanalysis and electron backscatter diffraction. The structural and compositional changes as a result of the tellurium inward diffusion will be analyzed with the high resolution transmission-electron-microscope. The effect of grain boundary character distribution on the propagation of tellurium-induced grain boundary cracking will be correlated with the topology of the grain boundary network. The composition and microstructure of the fracture surface and the crack-tip of the intergranular cracks will be analyzed to reveal the mechanism of the grain boundary embrittlement induced by tellurium. The expected output of this project will provide the GBE technique for Alloy-N and look inside of the mechanism of tellurium-induced embrittlement of Alloy-N.

熔盐堆中使用的Alloy-N合金 (16Mo-7Cr-5Fe-Ni) 直接与承载核燃料的高温熔盐接触。裂变产物Te沿晶界扩散导致晶界脆性开裂是降低材料性能及使用寿命的最重要问题之一。本项目针对Alloy-N合金的晶界工程（GBE）技术，研究控制并提高合金低∑CSL晶界比例的工艺方法，以及特殊结构晶界形成、迁移和演化的规律。对GBE技术处理后含有大量特殊结构晶界的合金进行高温Te扩散，利用电子背散射衍射，电子探针和TEM等技术研究晶界结构类型对Te沿晶界扩散的影响，分析Te扩散导致晶界微区化学成分及结构变化规律。研究晶界特征分布对Te致晶界脆性开裂的影响，利用原位俄歇能谱仪分析断面上的元素分布，利用TEM分析裂纹尖端的成分及结构变化，揭示Te致晶界脆性开裂的机理。通过该研究得出适用于Alloy-N合金的GBE技术，为通过GBE技术提高Alloy-N合金抗Te致晶界脆性提供理论依据。

通过对熔盐堆中使用的Alloy-N合金的晶界工程（GBE）研究，获得了控制并有效提高合金低∑CSL晶界比例的工艺方法，探明了特殊结构晶界形成、迁移和演化的规律。将GBE技术处理后含有大量特殊结构晶界的合金样品在Te（碲）蒸汽环境中进行热处理扩散实验。Te不仅沿晶界向材料内部扩散而且会沿晶粒内某些低指数晶面扩散渗透。研究了晶界结构类型对Te扩散的影响，统计了渗透路径的深度及密度，表征分析了Te扩散导致微区化学成分及结构变化的规律。研究了合金形变及时效处理对Te向Alloy-N合金内部扩散的影响，以及晶界特征分布对Te致晶界脆性开裂以及合金力学性能和表面裂纹形态的影响，揭示了Te致晶界脆性开裂的机理。通过该研究得出了适用于Alloy-N合金的GBE技术，为通过GBE技术提高Alloy-N合金抗Te致晶界脆性提供了理论依据。