| As one of the most ideal ways to solve the human energy crisis and environmental pollution,magnetic confinement fusion faces many technical and material problems.Blanket system is an important part of the fusion to achieve energy conversion.But the solid blanket has many problems,such as difficulty of tritium extraction and heat removal,tritium breeding,carrying and cooling ability.The liquid metal blanket with the ability of tritium proliferation,transport and cooling is one of the most promising blanket schemes,and is the main scheme of liquid metal blanket for future fusion power stations.As a low atomic number material,liquid lithium has the characteristics of low cost,high tritium propagation rate,high thermal load transport capacity,and good compatibility with plasma,so it is considered as the main candidate material for tritium breeder,coolant and first wall in blanket module.However,lithium is a chemically active alkali metal,which is highly corrosive at high temperature and has certain destructive effects on blanket structural materials.In order to ensure the safe and stable operation of liquid metal blanket in the fusion reactor,it is of great significance to study the corrosion characteristics of liquid lithium at high temperature on blanket structural materials.For these cases,the corrosion characteristics of 316L stainless steel（316L SS）,CLF steel and CLAM steel with high-temperature liquid lithium were studied under 0.1 MPa Argon（Ar）atmosphere.In the thesis,the corrosion rate,microstructure change of morphology and composition,and macroscopic mechanical properties of these materials were analyzed.Compatibility of liquid lithium with these materials was evaluated.The main results are as follows:（1）The mass dissolution of 316L SS in liquid lithium is dominated by Cr and C elements,and the mass loss is 2.5×10-4(±6.8×10-5)g,mass loss rate is in the order of mg/（m2﹒h）,corrosion depth ratio is in the order ofμm/a,corrosion resistant grades is GradeⅠ.Due to the chemical reaction of Cr and C elements in liquid lithium,a small amount of Cr7C3 and Cr23C6 carbides are formed on the surface of 316L SS,which results in the increase of surface hardness.Because of the dissolution of Cr and C elements and the formation of carbides,liquid lithium permeates into the interior of the sample along the grain boundary,Because of the dissolution of Cr and C elements and the formation of carbides,liquid lithium permeates into the interior of the sample along the grain boundary,which is the reason of intergranular corrosion on the surface of 316L SS.Due to the selective dissolution of elements,the sample exhibits non-uniform corrosion and pitting corrosion,and the surface presents a residual substrate after element consumption.Compared with 304 stainless steel（304 SS）under the same experimental conditions,316L SS is more resistant to liquid lithium corrosion than 304 SS.（2）The corrosion behavior of CLF and CLAM steels in liquid lithium is also different at different experimental temperatures.When the temperature of liquid lithium is 600 K,the mass loss of CLF and CLAM steel was slight,and the mass loss was in the order of mg.And their corrosion depth rates are 6.3×10-4 mm/a and 6.4×10-4 mm/a,respectively,corrosion resistant grades are GradeⅠ.Corrosion products can be observed on the sample surface and distributed along grain boundaries.When the temperature of liquid lithium is 820 K,the mass growth rates are 1.7×10-3 g/（m2﹒h）and 3.9×10-3g/（m2﹒h）,respectively.The substrate cannot be observed on the surface of CLF steel sample,which is covered by attachments.However,the attachments have regular shape on the CLAM surface,and the substrate can be seen through the gap of the attachment,and the corrosion products distributed along the grain boundary,can be seen on the substrate.EDS results showed that Ni element existed on the surface of all the samples,and XRD results also showed that new phase of Fe Ni appeared on the surface of all the samples.This indicates that the material of experimental device occurs element migration,and element migration is the main reason for the appearance of Ni element on the sample surface.It can be found from the above experimental results that element migration is related to temperature.When the experimental temperature increases,element migration becomes more serious,and the corresponding surface has a higher Ni element content.Through the above experiments and research results,the corrosion behavior of 316L SS,CLF and CLAM steel in liquid lithium is understood.The corrosion mechanism of these materials in liquid lithium is revealed.These results provide data reference for the application of lithium and related materials in liquid metal blanket,and provide early warning for the potential corrosion safety risk of liquid lithium blanket in the future fusion reactor. |
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