自由體積對(duì)塊體非晶斷裂韌性的影響

Zhen-DongZhua,EvanMab,JianXua,*

Intermetallics46(2014)164e172ElevatingthefracturetoughnessofCu49Hf42Al9bulkmetallicglass:Effectsofcoolingrateandfrozen-inexcessvolume

目錄03ResultsandDiscussion02

Experimental01AbstractandIntroduction04ConclusionsAbstractandIntroduction

Herewedemonstratethatbyincreasingthecoolingrateduringthecastingofliquid

Cu49Hf42Al9intoBMG,usingamixedargonandheliumatmosphere,thenotchtoughnessoftheresultant

BMGcanbe

tripled

relativetothatobtainedatslowercoolingrates.Themuchelevatedtoughnessis

attributedtoaten-foldincreaseinthesizeoftheplasticzoneatcracktip,duetotheproliferationof

shearbandingfacilitatedbyenhancedpropensityforsheartransformations.Thelatterpropensityis

explainedbythereducedshearmodulusandmicrohardness,aswellasincreasedenthalpyrecovery,all

ofwhicharerootedinstructuraldisorderasreflectedbythelowereddensityand

increasedfrozen-in

excessvolume.Suchastructure-propertycorrelationissystematicallydemonstratedbymonitoringall

thesepropertiesoverarangeofdiametersoftheas-castBMGrodsthatcorrespondtocooling

ratelevels

from40K/sto103K/s.AbstractandIntroduction

Movingforwardfromthesepreviousstudies,inthispaperwefocusourattentionon

aquantitativeassessmentofthe

possible

changeof

fracturetoughnessinducedbythe

variationofcooling

rate.

Thenotchtoughness

characterizedinthisstudyshowedalargeincreaseforthecoolingraterangeemployed.

Inadditiontofracturetoughness,wewill

alsoexaminetheeffectofcoolingrateonseveralproperties

includingthedensity,microhardness,enthalpyrecovery,andelasticconstants,whichareallexpectedtodependon,andthusto

beindicatorsof,theBMGinternalstructure.Suchasystematic

characterizationprovidesuswithacomprehensivepictureofthechangesintheBMGstructureandmechanicalresponses,and

shedslightontheoriginresponsiblefortheBMGtoughening

observed.

Experimental1.在Ar氣保護(hù)氣氛下，使用同模鑄造法制備2-10mm不同直徑theCu49Hf42Al9BMGrods2.數(shù)據(jù)的測(cè)定1)密度的測(cè)量是通過阿基米德法測(cè)的2)維氏硬度的測(cè)量是用MVR-HS硬度計(jì)在加壓300N。保溫時(shí)間20S測(cè)得。顯微硬度值是20個(gè)個(gè)體測(cè)量的平均值。并且才三個(gè)不同的點(diǎn)進(jìn)行測(cè)量。3)放熱焓變由DSC-Diamond;PerkinElmer,Shelton,CT在氧化鋁箱、流動(dòng)Ar氣保護(hù)、加熱速率0.33K/s測(cè)得4)Elasticproperties彈性特征由RUS（共振超聲分光鏡檢測(cè)）測(cè)得back

Experimental

5)缺口韌性的測(cè)量是通過不同冷卻速率下形成BMG板材測(cè)得

6)材料的斷裂韌性是通過測(cè)量單邊切口梁(SENB)測(cè)定。3PB(三點(diǎn)彎曲測(cè)試)是用Instron5848micromechanicaltester在線性位移(0.1mm/min)測(cè)得7）通過前面所的實(shí)驗(yàn)數(shù)據(jù)在ASTMstandardE399標(biāo)準(zhǔn)之下，得出缺口韌性的值。8）式樣斷裂面形貌在SEM下觀察。

ResultsandDiscussion3.1.Cooling-ratedependenceofthefrozen-inexcessvolumeand

hardnessFig.1.(a)ChangesofdensityandVickersmicrohardnessand(b)relative

changeof

frozen-inexcessvolume,asafunctionofthediameterofas-castCu49Hf42Al9BMGrods.ResultsandDiscussion3.2.Correlationoffrozen-inexcessvolumewithenthalpyrecoveryResultsandDiscussionFig.3.Correlationbetweenrelativechangeofexcessvolumeandenthalpyrecovery(DH)associatedwithstructurerelaxationofCu49Hf42Al9BMGfabricatedwithdifferentglass-formingcoolingrates.Thedashlineisfromlinearfitting3.2.Correlationoffrozen-inexcessvolumewithenthalpyrecoveryResultsandDiscussion3.3.Correlationoffrozen-inexcessvolumewithelasticconstantsFig.4.Changeof(a)shearmodulus(G)andbulkmodulus(B)and(b)Young’smodulus

(E)andPoisson’sratio(n)withroddiameterofas-castCu49Hf42Al9BMG.材料性能對(duì)冷卻速率的敏感性歸納為：Hv>(GorE)>泊松比>密度ResultsandDiscussion3.3.Correlationoffrozen-inexcessvolumewithelasticconstantsResultsandDiscussion3.4.Effectofglass-formingcoolingrateonnotchtoughness（缺口韌性）ResultsandDiscussion總結(jié)冷卻速度↑

↑維氏硬度↓密度↓B↑泊松比↑

↑粘度↓斷裂韌性↑

↑能量釋放率↑缺口韌性↑源于ConclusionsIncreasingthecoolingrateduringBMGfabrication,suchas

castingunderargonatmospheremixedwithhelium,hasa

remarkableeffecttosignificantlyimprovethetoughnessofBMGTheenhancedBMG

toughnessisassociatedw