简介：Surfacenanocrystallization(SNC)hasprovedtobeaneffectiveapproachtoimprovetheoverallpropertiesofbulkmetallicmaterials.Recently,anewsurfacenanocrystallizationtechnique,i.e.,surfacemechanicalgrindingtreatment(SMGT),wasdeveloped.Inthiswork,agradientnano-microstructurewasachievedinthesurfacelayeroftheAISI52100steelbyusingSMGT.Weobtainedaminimumgrainsizeofabout7nminthetopsurfacelayer.Thetotalthicknessofthedeformedlayerisover200micrometer.Meanwhilethesurfaceroughnessisratherlow.Ferritegrainsweredeformedtodifferentextentsvaryingwithdepthfromthetopsurface.Gradientgrainsizeswereformedfromtopsurfacetodeepmatrixwhichofferedagreatopportunitytostudytherefinementprocessoftheferritegrains.Itisfoundthatdislocationactivitiesplayadominantroleintheprocess.Attheinitiatestage,dislocationsaccumulatedandinteractedtoformdensedislocationwallsandcells.Increasingstrainandstrainrateinducedmoredislocationwallsincells,formingfinercells.Thisprocedurecontinueduntilnanograinsformedatthetopmostsurface.Theexistenceofcementiteparticlesinferritematrixgreatlyfacilitatestheferriterefinementprocess.Boundariesbetweenferritesandcementitesofferedmanydislocationsourceswhichacceleratethepropagationofdislocations.Dislocationwallswereblockedbycementiteswhichcertainlyleadtofinerdislocationcells.Theexistenceofcementitesmakesiteasiertogeneratefreshdislocationwallsinsub-microngrains.Astraingradientwasformedfromacementiteparticletosurroundingferritegrains.Thisstraingradientgivesrisetomoregeometricnecessarydislocations.Asferritegrainsizedecreasedlessthanthatofcementiteparticles,fragmentationoccurredincementites.Hardsecondphasewasusuallyconsideredasbrittle.Inthiswork,evidencesofdeformation(tracesofdislocationactivities)incementitesweredistinct.Sincethestressconcentrationinthephaseboundary(espec

简介：Recentinvestigationsindicatedthatmetalscanbeeffectivelystrengthenedbynumeroustwinboundaries(TBs)withtwin/matrixlamellarthicknessesinthenanometerregime.Superiorstrength-ductilitysynergieshavebeenachievedwiththenano-twinstrengtheningmechanism.Inthistalk,thenovelnano-twinstrengtheningwillbeappliedtoaustenitesteelsincluding316LstainlesssteelandaFe-Mnsteelinordertooptimizetheirstrength-ductilitycombinations.Thesteelsareprocessedbymeansofdynamicplasticdeformation(DPD,i.e.,plasticdeformationathighstrainrates).Single-phased(austenite)bulknanostructuredsteelspecimenswereprepared,consistingofnano-sizedgrainsembeddedwithnano-scaletwinbundles.Theas-preparednanostructuredsampleswereannealedatvariousconditions,resultinginpartialrecrystallizationofthenanostructuresandformingamixturestructureofcoarse-grainsembeddedwithnano-twinbundles.Strengthandductilityoftheaustenitesteelswithdifferentamountofnano-twinbundlesareanalyzed.Measurementsshowedthenano-twinstrengthenaustenitesteelscanbesuperstrong(withyieldstrengthabove1GPa)togetherwithaconsiderableductility(elongation-to-failure>20%).