Investigation Of Bubble's Formation And Evaluation In Tungsten By Helium Implantation

Tungsten(W)has been selected as one of the candidates for PFMs due to its great properties of high melting point,strong anti-sputtering ability,no reaction with hydrogen,low deuterium retention and long service life.However,in practical situations,the high-energy neutrons generated by the helium reaction will react with nuclei in the material through(n,?)and(n,p)reactions.This process produces a large amount of low-energy,strong-flow hydrogen and helium ions.The interaction of these high-energy neutrons,hydrogen and helium ions with tungsten materials will lead to radiation swelling and deformation.Therefore,it is necessary to study the interaction between helium ions and tungsten for the conceptual design of fusion reactor materials.This dissertation focuses on the formation and evolution of helium bubbles in polycrystalline tungsten materials.In the experiment,helium ions were implanted into the prepared polycrystalline tungsten samples by ion implantation method,and then the surface microstructures of the injected samples were characterized by scanning electron microscope and atomic force microscope to study the relationship between irradiation dose,polishing method,lattice orientation and helium bubbles in tungsten.The following are four conclusions drawn from this work:(1)The polycrystalline tungsten sample used in the experiment has a layered structure.The layered structure is produced by the hot rolling process when obtained high-purity tungsten by powder metallurgy.The extrusion deformation of the grains is caused by the high pressure during the rolling process.(2)The average surface roughness,swelling degree,and bubble size of the tungsten sample surface will increase with the irradiation dose.However,the bubble size will reach a maximum at a critical dose(1.80),and increasing the dose will cause the bubble to burst;(3)The electropolishing samples are observed better experimental phenomena than mechanical polishing samples after irradiation,and also better reflected the irradiance dependence of helium bubbles on the surface of tungsten samples.Therefore,under the condition of experimental conditions,it is recommended to choose electrolytic polishing samples;(4)From the result of the electrolytic polished specimens after irradiated by helium ions,we can found that the shape and dietribution of the helium bubbles were more regular than mechanical polished specimens,which means that mechanical polishing method would induced new damage to the surface of the material.