Alumina-basednanocompositesconsolidated bysparkplasmasintering Guo-DongZhan,JoshuaKuntz,JulinWan,JavierGaray,AmiyaK.Mukherjee * Department of Chemical Engineering and Materials Science, University of California, One Shields Avenue, Davis, CA 95616, USA Received27August2001;receivedinrevisedform26November2001;accepted27May2002 Abstract Sparkplasmasinteringisanewprocessbywhichceramicsandcompositescanbeconsolidatedveryrapidlytofull density.Inthepresentstudy,piezoelectricNd 2 Ti 2 O 7 secondphasetougheningnanocrystallinealuminacompositeswith highertoughnessweresuccessfullydevelopedatrelativelylowtemperaturesthroughthistechnique. Ó 2002ActaMaterialiaInc.PublishedbyElsevierScienceLtd.Allrightsreserved. Keywords: Alumina-basednanocomposites;Sparkplasmasintering;Piezoelectricphasetoughening;Hardnessandtoughness 1. Introduction It is believed that nanocrystalline ceramics ex- hibitadramaticchangeintheirpropertiesoverthe conventionalceramicmaterialsduetothepresence of extremely fine crystallite size, typically of the orderof100nmorless.Todate,asignificantlevel of research effort has been directed toward syn- thesizingnanocrystallineceramics[1–6].However, nanocrystallineceramicsdonotappeartopossess fracture toughness apparently any higher than conventionalmicrocrystallineceramics.Duetothe difficulty in material processing, especially in alu- mina nanoceramics, there has been very limited information about the toughness of nanocrystal- line ceramics. Therefore, it is very likely that, in spiteofthesignificantadvantageinotherproper- ties, toughness might become the bottleneck that controlstheapplicationofnanocrystallineceram- icsforstructuralcomponentsinservice. Domain switching as a toughening mechanism has been recognized in ferroelectric–ferroelastic materials where either an applied compressive stressorelectricalfieldledtodomainswitching[7]. Moreover, piezoelectric ceramics are capable of converting mechanical energy to electric energy andviceversa.Basedonthedomainswitchingor/ and piezoelectric effect in ferroelectrics or piezo- electric ceramics, a new toughening mechanism wasappliedandproveninnanocrystallinealumina nanocomposites.Inthepresentstudy,neodymium titanate(Nd 2 Ti 2 O 7 )wasselectedasapiezoelectric toughening second phase for high temperature application because it exhibited piezoelectric and electro-opticpropertiesandhadaCurietempera- ture in excess of 1500 °C [8]. The addition of a piezoelectric phase (Nd 2 Ti 2 O 7 ) to the alumina matrixisexpectedtoincreasetougheningbycon- verting stress–strain energy to electrical energy ScriptaMaterialia47(2002)737–741 www.actamat-journals.com * Correspondingauthor.Fax:+1-530-752-9554. E-mail address: akmukherjee@ucdavis.edu (A.K. Mukher- jee). 1359-6462/02/$-seefrontmatter Ó 2002ActaMaterialiaInc.PublishedbyElsevierScienceLtd.Allrightsreserved. PII:S1359-6462(02)00191-4