简介:Precipitationstrengtheningaswellassolutionstrengtheningiskeymechanismforheatresistantsteels.Itisveryimportanttocharacterizetheprecipitatesin9%Crferriteheatresistantsteels,especiallytoshowthenanometer-sizedparticles.Bytransmissionelectronicmicroscopeattachedwithanenergydispersivespectrometeraswellasopticalmicroscope,scanningelectronicmicroscope,themicrostructureandchemicalcompositionofprecipitatesina9%Crheatresistantsteelafterdifferentheattreatmentswereinvestigated.ItwasfoundthatthemicrostructureofnormalizedsamplewasmartensitewithfineNbCandFe3C.Themicrostructureoftemperedsampleistemperedmartensite,andtheremainlyweretwotypesofprecipitates,M23C6withthesizerangeof50-300nmandMXwiththesizeof10-100nm.SuperfineM23C6precipitatedpreferablyonpriorausteniticgrainboundariesandmartensiticlathboundaries,whilenanometer-sizedMXprecipitatesweredistributedrandomly.Aftershort-termcreep,Lavesphaseformedalonggrainboundariesofthe9%Crsteel,andM23C6andMXprecipitateswerefoundtobecomecoarser.Moreinformationaboutprecipitatesinthe9%Crsteelhadbeenexhibitedbyatomicforcemicroscopy.Thereby,distribution,sizeandshapeoftheprecipitatesaswellastheircompositionsandstructureswererevealed.
简介:Inthiswork,boththethermalexpansionandelectricalconductivityofnanocrystallineLa2Mo2O9werestudied.ThenanocrystallinepowderofLa2Mo2O9wasobtainedbysol-gelmethod,andwiththehelpofSHP(superhighpressure)upto4.5×104atmat700℃forashorttime,andthenanocrystallinepowderwasdensifiedwithoutobviousparticlesizegrowth.TheelectricalconductivityofnanocrystallineLa2Mo2O9wasoneorderofmagnitudelowerthanthatofthemicrocrystallinesampleatthesametemperature.Owingtothephasetransition,themicrocrystallineLa2Mo2O9hasanabruptincreaseofthermalexpansionwithapeakvalueof48×10-6K-1at556℃.Forthenanocrystallinematerial,thepeakvalueincreasesto112×10-6K-1at520℃.Ontheotherhand,above600℃thesignificantgrowthofparticlesizeofthenanocrystallineLa2Mo2O9wasobserved,accompanyingbyatremendousincreaseofthermalexpansionwithapeakvalueofthirdhigherthanthatofLa2Mo2O9.
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