حامد صمدی

The combinedeffectsofSiCandcarbonadditivesonthedensification, structureandcharacteristicsofpressurelesssinteredZrB2–SiC ceramic composites werestudied.TheZrB2–SiC (1–10 wt%)compositepowdersweremixedby1–2 wt%carbon.Thepreparedpowdermixtureswere then cold-consolidatedandsinteredinargonenvironmentinthetemperaturerangeof1800–2100 1C for2h.Theconstitutedphasesand microstructural evolutionswerestudiedusingx-raydiffractionandscanningelectronmicroscopeequippedwithanenergydispersivex-ray detector. Theobtainedresultsconcludedthatthedensification wasincreasedbyextendingthesinteringtimeandalsobypriorholdingof specimens at1650 1C. ThiscausedbyreductionofsuchoxideimpuritiesofZrO2, B2O3 and SiO2 on particlesurfacesviatheformationofnew phases inthesystem.However,thiswastotallyinducedtheenhancementofsinteringphenomenon.ThepresenceofSiCwithaveragegrainsize smaller thanthatforZrB2 revealed toaidthedensification byenhancinggreenspecimendensity.Furthermore,incrementofthecarboncontent through erosionofmillingmediainhibitedthematrixgraingrowth.BothofSiCandcarbonadditivesseemedtoenhancethereductionofoxides formation. TheadditionofSiCandcarbonwasfoundtobeadvantageousfordensification upto99.5%ofthetheoreticaldensity.Accordingto the examinations,itwasdemonstratedthatthespecimenstrengthwasvariedwithadditionsofSiCandcarbon.Indentationtoughnessofthe samples wasexaminedandresultsexemplified toughnessincrementwithSiC.However,carbonhadadetrimentaleffectonfracturetoughness. The microhardnessvalueswereincreasedwithincreasingSiCandcarboncontentduetothereductionofporosityvolumepercentagein specimens.