Atomic Study Of Helium Behaviors At Fe/Mn₆Ni₁₆Si₇ And Fe/graphene Interface

Nuclear energy has been widely studied and applied due to its characteristics of clean,pollution-free,and sustainable development.Over the past few decades,nuclear power has become a reliable way to the energy usage for human beings.In recent years,with the development of the generation-IV and fusion nuclear reactors,radiation damage of structural materials becomes one of the greatest challenges.It is urgent to develop radiation-resistant structural materials those suitable for advanced reactor concepts.However,few traditional materials are available for the corresponding extreme operating conditions.Thus,it is necessary to develop new concept structural materials those can tolerant the radiation environment.The introduction of high-density interfaces can play a positive role in the behaviors of irradiation induced defects and is a well-known strategy for the purpose.Helium（He）atoms produced by nuclear transmutation reaction tend to gather at the interface,which results in the deterioration of mechanical properties of materials.In this thesis,the stabilization and diffusion behaviors of He atoms at Fe/Mn₆Ni₁₆Si₇ and Fe/graphene interfaces have been investigated at the atomic scale using first-principles.Mn₆Ni₁₆Si₇is an important precipitate formed at grain boundaries of ferrite/martensite by solute atoms segregation.The He atom behaviors at Mn₆Ni₁₆Si₇,α-Fe matrix,and Fe/Mn₆Ni₁₆Si₇ interface are studied.We found that the Mn₆Ni₁₆Si₇ precipitate is the trapping site,and He atoms prefer to stay at the interface of Fe/Mn₆Ni₁₆Si₇.Furthermore,the presence of He atoms both in Mn₆Ni₁₆Si₇ precipitate and at the interface can promote the formation of vacancies.Recently,studies have shown that metal/graphene composites have better ability in the radiation resistant than that for the corresponding pure metal materials.As is known,stainless steels with Fe as main matrix are widely used in nuclear systems.In order to explore whether stainless steel/graphene has potential radiation resistance,we investigated the behaviors of He atoms and intrinsic defects at the interface of Fe/graphene by first principles calculations.A strong interaction between iron and graphene was found.Compared withα-Fe matrix and graphene,the formation energy of inherent defects at interface is lower.Furthermore,He atoms have large diffusion barriers and binding energy at interface,which indicates that it is difficult for He atoms to enter into the interface.Once He atoms enter into the interface,they can be trapped well,indicating that the interface as a sink of defects.The above results show that:the introduced interface can increase the stable sites of He atoms.It can reduce the concentration of He in the matrix.The theoretical results in the thesis helps us to understand the influence mechanism of the interface on the aggregation behavior of the transmutation element He from a microscopic point of view.