ActaMaterialia52(2004)3507–3517www.actamat-journals.comAnewmethodtoevaluatethefracturetoughnessofthinfilmsZhenhaiXia,W.A.Curtin,B.W.Sheldon*DivisionofEngineering,BrownUniversity,BoxD,Providence,RI02912,USAReceived5February2003;receivedinrevisedform28July2003;accepted3April2004Availableonline10May2004AbstractAmethodbasedonmicroindentationisdevelopedtodeterminethefracturetoughnessKIcofathinfilmbondedtoabrittlesubstrate.Usinganeasilyfabricatedsamplehavingapartiallycoatedsubstrate,indentationontheuncoatedportionofthesubstrateisusedtogeneratearadialcrackthatpropagatesintoandawayfromthecoatedregion.Comparisonofthelengthsofthesurfacetracesoftheindentationcrackintoandawayfromthecoatedregionisusedtomeasurethetougheningimpartedbythecoating.Thistestmethodavoidsthecomplicatingeffectsofdelaminationthatoftenoccurwhenthecoatingisindenteddirectly.Toextractquantitativeresults,a3Dfiniteelementmodelofthesystemgeometryisgeneratedandacohesivezonemodelisusedtopredictthecomplexequilibriumcrackfront.Themodelpredictsthelengthofthecrackpenetrationintothecoatingvs.thelengthofthecrackgrowthawayfromthecoatingasafunctionoftheelasticandtoughnesspropertiesofthecoatingandthesubstrate,andtheresidualthermalstresses,whichplayanimportantcontributiontothedetailedcrackgrowth.Anapproximateanalyticmodelusingenergybalanceideasisdevelopedtopermiteasydeterminationofthecoatingtoughnessfromexperimentaldata,andthemodelagreeswellwithfullnumericalresultsoverawiderangeofcoatingandsubstratepropertyvalues.Theoverallmethodisappliedheretode-terminethetoughnessofathinCVDdiamondcoatingonathicksiliconsinglecrystalsubstrate,andacoatingtoughnessof1=2KIc¼8:4MPamisobtainedusingapreviouslymeasuredbiaxialtensilecoatingresidualstressof1GPa.Ó2004ActaMaterialiaInc.PublishedbyElsevierLtd.Allrightsreserved.Keywords:Thinfilms;Fracturetoughness;Indentation1.Introductiontion,whichiswellsuitedtoinsitutestingoffilmsandsmallvolumes,havebeendevisedtomeasureKIc.FracturetoughnessisanimportantpropertyforMicro-and