Processing of alumina-zirconia composites by surface modification route with enhanced hardness and wear resistance

Zirconiatoughenedalumina(ZTA)materialsarefrequentlyusedinmechanicalengineeringandbiomedicalapplicationsduetotheirenhanced toughness,strengthandwearresistance comparedtomonolithicalumina.Inthis study, asubmicronsizealuminapowderwasmodified via wet chemical route: thealuminaparticlessurface wascoatedwithzirconiumchloride,toyield10vol%zirconiabysubsequentthermaltreatment.Fromthispowder, severalZTAmaterialswereproducedbyslipcasting,sinteredatdifferenttemperaturesfrom1475to1575 1C. Inallmaterials,afullcharacterizationof their mechanicalproperties,microstructureand phasecompositionwascarriedout,togetherwithwear testscarriedoutinalinear-reciprocating modeusing a Y-TZPballcounterpartunder environmental conditions. The resultsshowlowwearatsinteringtemperaturesbelow1525 1C andhighwearathighersinteringtemperatures,whichcanbewell correlated tothehardness,microstructureandphaseevolution.Themicrostructureofthematerialsisinitiallyextremelyhomogeneousand fine grained. Thegrainsizeincreasesmoderatelybothforthezirconiaandaluminacomponentswiththesinteringtemperaturesconsidered.Thegrain shape ofaluminagraduallychangesfromisometrictoelongated.Upto1525 1C, thesizeofzirconiagrainsstaysbelow400nm.Thezirconia transformability wasevaluatedanditwasobservedthatthezirconiadispersionremainsvastlyuntransformableuptothatsinteringtemperature.In this condition,thealuminamatrixisundercompressivehydrostaticstressandfractureresistanceismoderate.Athighersinteringtemperatures, grain growthinduceshigherzirconiatransformabilityandfractureresistancebutattheexpenseofhardnessandwearresistance.Thesimultaneous evolution oftabularmorphologyinmatrixgrainsalsocontributestotoughnessbutfacilitatesgrainbreakoutanddisruptionofthesurfaceduring final machiningandundertribologicalload.