High entropy alloys: study of structural properties and irradiation response
Date
2016-07-01
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Abstract
Järgmise põlvkonna tuumaelektrijaamades kasutatavad materjalid peavad toimima ekstreemsetes keskkonnatingimustes nagu tugev kiiritus, kõrge temperatuur ning tugev korrosioon. Uudne materjalide klass - kõrge entroopiaga sulamid - on üks võimalikke kandidaate tuumarakendusteks tänu nende sobilikele omadustele. Kõrge entroopiaga sulamid koosnevad viiest või enamast põhielemendist ning moodustavad ühefaasilise tahke lahuse. Seni on neid vähe uuritud kiirituskoste seisukohast. Kuna eksperimendid ei ole võimelised uurima kiirituse toimel tekkivaid protsesse tänu nende kiireloomulisusele, tuleb nende uurimiseks kasutada arvutisimulatsioone. Simulatsioonide tulemused sõltuvad kasutatavatest mudelitest ning seetõttu tuleb uurida erinevaid tulemusi mõjutavaid põhjusi. Käesolevas töös uuriti kolme aspekti, mis võivad mõjutada kiiritussimulatsioone. Esiteks arvutati aatomite vaheline lähimõju kristallis, kasutades kvantmehaanika meetodeid. Saadud tulemuste põhjal loodi uus meetod empiiriliste potentsiaalide modifitseerimiseks nii, et potentsiaalidest saadud lähimõju oleks kooskõlas kvantmehaanika arvutustega. Teiseks uuriti kahe kõrge entroopiaga sulami - NiCrCo ja NiCrCoFe - struktuuriomadusi arvutisimulatsioonidega. Tulemustest selgus, et elemendid ei ole vaadeldavates materjalides juhuslikult jaotunud, mida aga üldjuhul eeldatakse kõrge entroopiaga sulamites. Kolmandaks arvutati elektronide pidurdavat toimet kiiresti liikuvale aatomile, kasutades selleks kvantmehaanika meetodit. Leitud tulemuste rakendamiseks klassikalistes simulatsioonides loodi uudne mudel ning rakendati seda Ni kristallis ja NiFe sulamis võrevõnkumiste kustumise uurimiseks. Kõik eelpool kirjeldatud uuringud annavad olulist informatsiooni kiiritussimulatsioonide teostamiseks kõrge entroopiaga sulamites.
Materials used in the next-generation nuclear plants have to withstand extreme environmental conditions, such as high doses of radiation, high temperature, and corrosive environments. Novel class of materials, called high entropy alloys, has been identified as a suitable candidate for use in nuclear applications due to their improved properties. High entropy alloys consist of five or more principal elements and form a single phase solid solution. However, they have not yet been studied thoroughly for radiation resistance. As experimental methods are not capable of studying radiation damage processes in detail, computational methods have to be used instead. The results obtained from computer simulations are susceptible to the quality of models used. Therefore, the study of aspects affecting radiation damage simulations of high entropy alloys are required. In the current work three aspects that could affect the results of simulations were investigated. First, the short-range interaction was studied with quantum mechanical methods to look at the effect of the medium on the energy required to bring two atoms close to each other. Based on the results, a method for modifying interatomic potentials was proposed and applied to the study of Ni crystal. Secondly, the distribution of elements was studied with a computer simulation in NiCrCo and NiCrCoFe random alloys. It was shown that the atomic structure in these materials is not totally random and should therefore be taken into account when performing computer simulations. Finally, the electronic effects on the stopping of a projectile in a Ni crystal were calculated from quantum mechanical calculations. A novel model was developed to include the effects of electrons on the atoms in a crystal. The model was applied to study the lifetimes of lattice vibrations in Ni and NiFe crystal. In conclusion, all the studied aspects provide important information for radiation damage studies of high entropy alloys.
Materials used in the next-generation nuclear plants have to withstand extreme environmental conditions, such as high doses of radiation, high temperature, and corrosive environments. Novel class of materials, called high entropy alloys, has been identified as a suitable candidate for use in nuclear applications due to their improved properties. High entropy alloys consist of five or more principal elements and form a single phase solid solution. However, they have not yet been studied thoroughly for radiation resistance. As experimental methods are not capable of studying radiation damage processes in detail, computational methods have to be used instead. The results obtained from computer simulations are susceptible to the quality of models used. Therefore, the study of aspects affecting radiation damage simulations of high entropy alloys are required. In the current work three aspects that could affect the results of simulations were investigated. First, the short-range interaction was studied with quantum mechanical methods to look at the effect of the medium on the energy required to bring two atoms close to each other. Based on the results, a method for modifying interatomic potentials was proposed and applied to the study of Ni crystal. Secondly, the distribution of elements was studied with a computer simulation in NiCrCo and NiCrCoFe random alloys. It was shown that the atomic structure in these materials is not totally random and should therefore be taken into account when performing computer simulations. Finally, the electronic effects on the stopping of a projectile in a Ni crystal were calculated from quantum mechanical calculations. A novel model was developed to include the effects of electrons on the atoms in a crystal. The model was applied to study the lifetimes of lattice vibrations in Ni and NiFe crystal. In conclusion, all the studied aspects provide important information for radiation damage studies of high entropy alloys.
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Keywords
sulamid, entroopia, kiiritus, kompuutersimulatsioon, alloys, entropy, irradiation, computer simulation