DENSE ZIRCONIA-SIC PLATELET COMPOSITES MADE BY PRESSURELESS SINTERINGAND HOT-PRESSING

2.6 mol% Y-TZP composites with up to 30 vol% SiC platelet additions we re fabricated by hot pressing and pressureless sintering to densities above 93%. Borosilicate glass additions aided densification, reduced t he thermal mismatch stress between the matrix and the platelets, and r educed grain growth rates in the mildly reducing atmosphere employed S trength was reduced (up to 50% in hot-pressed material and 60% in pres sureless-sintered composites) by the addition of up to 20 vol%; platel ets as a result of increased flaw size and tensile thermal mismatch st resses in the matrix. With a matrix grain size of 0.71 mu m, platelets increased toughness (from 7.0 to 8.3 MPa rim for a 30 vol% addition) while the amount of transformation decreased from 33 to 22%, demonstra ting that mechanisms such as crack deflection were present. Conversely , where the composite was processed to give a matrix grain size which optimised transformation toughening (greater than or equal to 0.85 mu m), the addition of the platelets led to a reduction in toughness (fro m 14.0 to 8.8 MPa root m for a 30 vol% addition). The volume fraction tetragonal which transformed during fracture to monoclinic zirconia de creased with platelet addition, for all processing conditions. The com posite toughness was always lower than the maximum in the monolith ari sing from transformation toughening alone, due to a low fracture stres s in the composite and modulus load transfer both of which reduce the transformation zone size. (C) 1997 Elsevier Science Limited.