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1、JournalJ.Am.Ceram.Soc.,81[11]2821±30(1998)MicrostructuralDesignofSiliconNitridewithImprovedFractureToughness:I,EffectsofGrainShapeandSizePaulF.Becher,*EllenY.Sun,*KevinP.Plucknett,*,²KathleenB.Alexander,*,#Chun-HwayHsueh,*Hua-TayLin,*ShirleyB.Waters,andC.GaryWestmorelandOakRidgeNationalLaboratory,Oa
2、kRidge,Tennessee37831-6068Eul-SonKangAgencyforDefenseDevelopment,Taejon,RepublicofKoreaKiyoshiHirao*andManuelE.Brito*NationalIndustrialResearchInstitute,Nagoya,JapanTheuseofself-reinforcementbylargerelongatedgrainsinnormaltotheprismfaces.6,7Suchgraingrowthoccursinthesiliconnitrideceramicsrequiresjud
3、iciouscontrolofthepresenceofaglassphasederivedfromthenativesurfaceoxidemicrostructuretoachievehighsteady-statetoughnessandonthesiliconnitridepowdersandadditivesusedtoenhancethehighfracturestrength.Withadistinctbimodaldistributiondensificationofthesiliconnitrideceramics.Theadditivesaf-ofgraindiameter
4、s,suchasthatachievedbytheadditionoffecttheglassviscositybyalteringtheglasscomposition.8,92%rodlikeseeds,thefractureresistancerapidlyriseswithWhengrowthoftheb-grainsiscontrolledbydiffusionthroughcrackextensiontosteady-statevaluesofupto10MPa?m1/2theglassphase,changesinglasscompositionmodifythedif-andi
5、saccompaniedbyfracturestrengthsinexcessof1fusionratesofsiliconandnitrogenand,thus,therateofgrainGPa.Whenthegenerationofelongatedreinforcinggrainsgrowth.7Inthecaseofinterface-controlledgrowthofthelargerisnotregulated,abroadgraindiameterdistributionistypi-b-grains,itisnotclearthatthechangesincompositi
6、onwithincallygenerated.Whilesometougheningisachieved,boththesameglasssystemwouldhavesignificanteffectsongrowththeplateau(steady-state)toughnessandtheR-curvere-rates.Ontheotherhand,substitutionofvariousrare-earthionssponsesuffer,andthefracturestrengthundergoesasub-canhaveasignificanteffectonthegrowth
7、ratesofb-grains.10stantialreduction.UnreinforcedequiaxedsiliconnitrideIntheearlierstudy,10itwassuggestedthatthegrowth-limitingexhibitstheleastR-curveresponsewithasteady-statestepshiftedfrominterfaceco
