Abstract
ZrO2-Naβ″-Al2O3 composites were prepared by a conventional method using two different powder routes and different milling liquids. The retained tetragonal-phase ZrO2 was 85 to 90% for composites with 2.4 to 15 vol% ZrO2. The fracture toughness (Klc) and strength increased with increasing ZrO2 content. At 20 vol % ZrO2,Klc and bend strength were 4.35 M Pa m1/2 and 390 MPa, respectively. Stress-induced transformation toughening is the predominant toughening mechanism. Dispersion toughening also contributes to the increase ofKlc. Surface strengthening was found to be an effective strengthening method for low ZrO2 levels. The critical tetragonal ZrO2 grain size was found to increase from 0.86 to 1.02gmm as the ZrO2 content increased from 2.5 to 15 vol %. A detailed study of the ionic conductivity of the 15 vol % ZrO2 dispersed sample was conducted by an a.c. technique between −124° C and ∼ 300° C. The bulk and total conductivities were calculated via complex-plane analysis. The total (grain and grain-boundary) ionic specific resistivity was ∼ 9 Ω cm at 300° C. The activation enthalpies of the bulk and total conductivity processes were 0.30 and 0.32 eV, respectively.
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