裂变产物碲致高镍合金GH3535晶间腐蚀研究

Intergranular Corrosion of High Temperature Ni-based Alloy GH3535 Induced by Fission Product Tellurium

熔盐堆的裂变产物溶于燃料盐中与结构合金直接接触,而碲会导致高镍合金产生晶间裂纹。为研究碲致合金晶间开裂机理,开展了GH3535合金在1、6和10 mg/cm^(2)碲浓度环境下的高温腐蚀实验。通过扫描电镜(SEM)、电子探针微区分析(EPMA)与透射电镜(TEM)等表征了腐蚀产物与碲扩散行为。在700℃碲气氛中腐蚀150 h后,合金试样表面呈现内外两层腐蚀层,外层反应层主要是Ni_(3)Te_(2)、Ni_(3)Te_(2.07)与Cr_(2)Te_(3),反应层厚度与碲浓度成正比关系;内层为碲扩散进基体形成的扩散层,由基体和许多长条状富碲相组成。碲沿晶界向内扩散到了更深处并在晶界富集,同时晶界出现明显的Ni、Fe、Cr的贫化,导致了晶间裂纹的产生。

In molten salt reactors,the interaction between fission products dissolved in the fuel salt with the structural alloys is a critical issue.Notably,the presence of tellurium(Te)poses a significant challenge by inducing intergranular cracks(IGC)for high temperature Ni-based alloys.Herewith,the corrosion behavior of high temperature Ni-based alloy GH3535 exposed to Te vapor(i.e.the test alloy with nominal doses of 1,6,and 10 mg/cm^(2) Te powders respectively were vacuum sealed in a quartz tube)at 700℃ for 150 h was assessed by means of scanning electron microscope(SEM),electron probe microanalyzer(EPMA),and transmission electron microscope(TEM),in terms of corrosion products and Te diffusion behavior.Results reveal that a dual-layered corrosion product was observed on the alloy surface after being exposed to Te vapor for 150 h at 700℃.The outer telluride layer comprised Ni_(3)Te_(2),Ni_(3)Te_(2.07),and Cr_(2)Te_(3),exhibiting a thickness directly proportional to the Te concentration.The inner ones represented a diffusion layer containing elongated Te-rich phases resulting from the inward diffusion of Te into the alloy matrix.Te diffusion was observed predominantly along grain boundaries(GB),penetrating to deeper regions and segregating there.It follows that the findings may provide a meaningful reference for understanding the Te-induced IGC,namely,this diffusion process led to a conspicuous depletion of Ni,Fe,and Cr at GB,thereby facilitating significantly the occurrence of IGC.