Abstract
Recently,a structurally-simplebutcompositionally-complex FeNiCoMnCr highentropyalloywasfoundto
haveexcellentmechanicalproperties(e.g.,highstrengthandductility).Tounderstandthepotentialof
using highentropyalloysasstructuralmaterialsforadvancednuclearreactorandpowerplants,itis
necessary tohaveathoroughunderstandingoftheirstructuralstabilityandmechanicalpropertiesde-
gradation underneutronirradiation.ThisrequiresustodevelopasimilarmodelalloywithoutCobe-
cause materialwithCowillmakepost-neutron-irradiationtestingdifficult duetotheproductionofthe
60Co radioisotope.Toachievethisgoal,aFCC-structuredsingle-phasealloywithacompositionof
FeNiMnCr18 wassuccessfullydeveloped.Thisnear-equiatomicFeNiMnCr18 alloy hasgoodmalleability
and itsmicrostructurecanbecontrolledbythermomechanicalprocessing.Byrollingandannealing,the
as-cast elongated-grained-microstructureisreplacedbyhomogeneousequiaxedgrains.Themechanical
properties (e.g.,strengthandductility)oftheFeNiMnCr18 alloy arecomparabletothoseoftheequiatomic
FeNiCoMnCr highentropyalloy.Bothstrengthandductilityincreasewithdecreasingdeformation
temperature,withthelargestdifferenceoccurringbetween293and77K.Extensivetwin-bandswhich
are bundlesofnumerousindividualtwinsareobservedwhenitistensile-fracturedat77K.Notwin
bands aredetectedbyEBSDformaterialsdeformedat293Kandhigher.Theunusualtemperature-de-
pendencies ofUTSanduniformelongationcouldbecausedbythedevelopmentofthedensetwin
substructure, twin-dislocationinteractionsandtheinteractionsbetweenprimaryandsecondarytwin-
ning systemswhichresultinamicrostructurerefinement andhencecauseenhancedstrainhardening
and postponednecking.