Degradationbehaviorof Mg-based biomaterials containing diffe

镁合金,LPSO

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SUBJECTAREAS:

MECHANICALENGINEERINGMETALSANDALLOYS

DegradationbehaviorofMg-basedbiomaterialscontainingdifferentlong-periodstackingorderedphases

QiumingPeng1,JianxinGuo1,HuiFu1,XuechengCai1,YananWang1,BaozhongLiu1,2&ZhigangXu3

12

Received18July2013Accepted

13December2013Published9January2014

StateKeyLaboratoryofMetastableMaterialsScienceandTechnology,YanshanUniversity,Qinhuangdao066004,China,SchoolofMaterialsScience&Engineering,HenanPolytechnicUniversity,Jiaozuo454000,China,3NSFEngineeringResearchCenterforRevolutionizingMetallicBiomaterials,1601EastMarketStreet,Greensboro,NC27411,USA.

Correspondenceandrequestsformaterialsshouldbeaddressedto

Q.M.P.

(pengqiuming@gmail.

com)

Long-periodstackingordered(LPSO)phasesplayanessentialroleinthedevelopmentofmagnesiumalloysbecausetheyhaveadirecteffectonmechanicalandcorrosionpropertiesofthealloys.TheLPSOstructuresaremostlydividedto18Rand14H.However,todatetherearenoconsistentopinionsabouttheirdegradationpropertiesalthoughbothofthemcanimprovemechanicalproperties.HereinwehavesuccessfullyobtainedtwoLPSOphasesseparatelyinthesameMg-Dy-ZnsystemandcomparativelyinvestigatedtheeffectofdifferentLPSOphasesondegradationbehaviorin0.9wt.%NaClsolution.Ourresultsdemonstratethatafinemetastable14H-LPSOphaseingraininteriorismoreeffectivetoimprovecorrosionresistanceduetothepresenceofahomogeneousoxidationfilmandrapidfilmremediationability.TheoutstandingcorrosionresistantMg-Dy-Znbasedalloyswithametastable14H-LPSOphase,coupledwithlowtoxicityofalloyingelements,arehighlydesirableinthedesignofnovelMg-basedbiomaterials,openingupanewavenueintheareaofbio-Mg.

M

agnesium(Mg)alloyshaveattractedagreatdealofattentionasorthopedicbiodegradableimplantmaterialsduetotheirpropermechanicalpropertiescomparabletonaturalboneandgoodbiocompat-ibility1.Incomparisonwithceramicsorpolymericmaterials,metallicMgmaterialsaremoresuitablefor

load-bearingapplicationsduetotheircombinationofhighmechanicalstrengthandfracturetoughness2.Moresignificantly,thedegradationproductisasoluble,non-toxicoxidesorhydroxideswhichcantemporarilyenhanceosteoblastactivityanddecreaseosteoclastnumberduringboneremodelling3.TheseintriguingcharacteristicshavemadeitpossibleforMgalloystobedevelopedintodegradablebio-Mgimplants.However,themainbottleneckofdegradablebio-Mgstentsliesinitsfastcorrosionratewhichleadstoweakmechanicalintegrity.Therefore,duringthehealingprocesstheycannotprovideenoughmechanicalsupport,resultinginbloodvesselrestenosis4.Consequently,thedevelopmentofnewbio-Mg-basedmaterialbecomesacriticalissue.

Recently,Mgalloyswithlong-periodstackingordered(LPSO)phaseshavebeenfoundinternaryMg-Zn-RE(RE5Y,Gd,Tb,Dy,Hoetc.)alloys5–7.ThemajortypesofLPSOstructuresinvolvethe18Rand14Hmodels.TherelationshipbetweenLPSOphasesandmechanicalpropertieshasbeenwellconfirmed.Suzukietal.8reportedthatasmallamountofZncanincreasethenumberofstackingfaultsinMg-Ybasedalloysbyintroducing18R-LPSOphase,whereinthemovementofdislocationscanbeprohibited,resultingintheimprovementoftensilestrength.Yamadaetal.9pointedoutthattheadditionofZnisattributedtotheformationof18R-LPSOphaseinMg-2.1Gd-0.6Y-0.2Zr(at.%)alloy,inwhichboththestrengthandplasticityareenhancedsignificantlyatlowtemperatures.Theseimprovedmechanicalpropertiesarewellelucidatedintermsoftheincrementofcriticalresolvedshearstressofbasalornon-basalslips10,theinterfacebetweenLPSOphaseandMgmatrix11andtheformationofkinkbands9,12–14.

Comparedtomechanicalproperties,theeffectofLPSOphasesoncorrosionpropertiesisunclear.Ingeneral,theLPSOphaseactsasaheterogeneousspot,andthenthepitting/galvaniccorrosionmightbeincreased15.However,Zhangetal.16recentlyreportedthattheas-extrudedMg-Gd-Zn-Zralloyexhibitalowanduniformcorrosionrateof0.17mm/yinHank’ssolutionowingtothepresenceof14H-LPSOphase.Zhaoetal.17verifiedthatthecorrosionpropertiesofMg-Zn-Yalloycontaining18R-LPSOphaseinsimulatedbodyfluidarebetterthanconventionalengineeringMgalloyssuchastheAZ31,WE43,ZK60andZX60alloys.Unfortunately,bothstudiesdidnotprovidedetailedmechanismswithrespecttotheselowdegradationrates.