PHASERELATIONSHIPSINR-FePSEUDOBINARYSYSTEM(R =Dy_(0.65)Tb_(0.25)Pr_(0.1))¥WANGBowen;WUCh angheng;ZHUANGYuzhi;JINXimei(InstituteofMet alResearch,ChineseAcademyofSciences,Shenyan g110015,China)(ShenyangInstituteofTechnolog y,Shenyang110023,China)Abstract:Thephaserel ationshipsofR-Fepseudobinarysystem(R=Dy0.65 Tb0.25Pr0.1)havebeendeterminedusingopticalm icroscopy,X-raydiffraction,EPMAandDTAtechni ques.Thissystemcontainsoneeutecticreactiona ndfourperitecticreactions.Thefourintermetal liccompoundsare(Dy,Tb,Pr)Fe2,(Dy,Tb,Pr)Fe3, (Dy,Tb,Pr)6Fe23and(Dy,Tb,Pr)2Fe17Thehomogen eityregionsofthesecompoundsshifttowardsrare earth-richsideofthestoichiometriccompositio nexcept(Dy,Tb,Pr)2Fe17.Keywords:rareearth-i ronalloy,phaserelationship,structure1.Intro ductionThemagneticbehaviorofrareearth-ironi ntermetalliccompoundsisofinteresttothetechn ologicalapplications,suchasthecoercivityand magnetostriction.Itisproposedthatthepseudob inaryLavescompounds,suchasTb(1-x)DyxFe2andT b(1-x)PrxFe2,possessrelativelylowmagnetocry stallineanisotropywhilstretaininghighroomte mperaturemagnetostriction[1,2].Theinvestiga tionofDy(0.9-x)PrxTb0.1Fe2alloysindicatesth atthemagnetostrictionexhibitsapeakwhenx=0.1 [3].AmaximummagnetostrictionofDy(0.9-x)TbxP r0.1Fe1.85alloysoccursatx=0.25[4].Inorderto giveaguidanceinthesearchfornewmaterials,iti snecessarytoknowthephaserelationshipsofR-Fe system.VanderGootandBuschowinvestigatedthes tructureandmagneticpropertiesofDy-Fesystem[ 5].Darieletal.reportedthephaserelationships ofTb-Fesystem[6].Theyallfoundthattherearefo urintennetalliccompounds(1:2,1:3,6:23and2:1 7)inthesetwosystems.DyFezandDyeFezsmeltperi tecticallybutDyFe3andDy2Fe17meltcongruently .TbFe2,TbFe3,Tb6Fe23andTb2Fe17allmeltperite ctically.ThereisonlyonecompoundPr2Fe17inthe Pr-Fesystem[7].ThephaserelationshipsoftheLa vescompounds(Tb0.27Dy0.73)Fexwith1.7≤x≤2.6i ntheTb-Dy-Feternaryphasediagramwereinvestig atedbyWestwoodetal[8].LandinandAgren[9]pred ictedthephasediagramof(Dy0.73Tb0.27)-Fepseu dobinarysystemaccordingtothermodynamicsandf oundthephaserelationshipsoftheLavescompound stobeconsistentwiththatreportedbyWestwoodet al[9].However,noreportofphaserelationshipsi nR-Fesystemisgiven.Inthepresentinvestigatio n,thephaseequilibriumofR-Fepseudobinarysyst emwasdetermined.2.ExperimentalProceduresThe alloyswerepreparedfrommaterialsofthefollowi ngpuritiesinwt%:Dy,Tu,Pr,99.9;Fe,99.8.Theal loysweremeltedinamagneto-controlledarcfurna ceunderhighpurityargon.Sincethevapourpressu reofDyisratherhigh,anextra3wt%Dywasaddedtoc ompensateforitsevaporationlossduringmelting .Theweightlossofeachsamplewascontrolledtobe low0.5%.Theas-castsampleswrappedinaMofoilwe resealedinasilicatubefilledwithhighpurityar gon.Theywerehomogenizedat1000℃for15d.Theetc hantformetallographicspecimensis2%—3%Nital. Thephasetransitiontemperaturewasdetenninedw ithanLCP-1typehightemperaturedifferentialth erinaldilatometer.X-raydiffractionanalysisw ascarriedoutonaD/max-rAdiffractometerequipp edwithapyrolyticgraphitemonochromator.CuKαr adiationwasused.Theelectronprobemicro-analy sis(EPMA)wasperfonnedinaCamebax-MicroAnalys er.3.ResultsandDiscussion3.1Intermetallicco mpoundeMetallographicexaminationandX-raydif fractionanalysesconfirmthattherearefourinte nnetalliccompoundsinR-Fesystem(R=Dy0.65Tb0. 25Pr0.1):(Dy,Tb,Pr)Fe2(Dy,Tb,Pr)Fe3,(Dy,Tb, Pr)6Fe23and(Dy,Tb,Pr)2Fe17,whicharesimilart othoseinDy-FeandTb-Fesystems.3.1.1(Dy,Th,Pr )Fe2Theas-caststoichiometricRFe2alloycontai nsasecondphaseandexhibitsacharacteristicper itecticstructure(Fig.1a).Afterhomogenizatio n,thesecondphaseparticlesdecreaseinnumberan dbecomebroaderinsize.Itwasidentifiedas(Dy,T b,Pr)Fe3phasebytheEPMAdata(Table1)andX-rayd iffractionanalysis.Atthesametime,Widmanstat tenprecipitateswereobservedwithinsomegrains .Thesimilarsituationof(Dy0.73Tb0.27)Fe2allo yhasbeenreportedbyWestwoodetal.[8].Indexing ofthepowderdiffractionpatternshowedthatthem atrixofthehomogenizedRFe2alloypossessescubi cMgCu2-typestructure,spacegroupofFd3manditslattieeparameter,α=0.7343nm,islargerthanthat(0.7325nm)ofDyFe2[5]andclosetothat(0.7346nm)ofTbFe2[10].FromtheEPMAdataofRFe2(Table1)
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