Synthesis and Mechanical Properties of Zirconia–Yttria Matrices/Alumina Short Fibre Composites

Abstract

Yttria tetragonal zirconia polycrystals (YTZP)/alumina short fibre (Al2O3-SF) composites were prepared by wet ball milling. Three different commercial powders of YTZP containing 2, 2.5 and 3 mol% of yttria (denoted as TZ2Y, TZ2.5Y and TZ3YA, respectively) were used as matrices, reinforced with 20 wt% Al2O3-SF. The effect of sintering conditions on the mechanical properties of the composites was studied. XRD and SEM techniques were used for the characterization of the prepared composites. The fracture toughness and hardness were determined by the Vickers indentation technique. The bend strength was measured using a four-point bending test machine. The results showed that both strength and toughness increase with yttria content. The TZ3YA/20 wt% Al2O3-SF composite showed bend strengths up to 760 MPa and fracture toughness of 9.2 MPa√m upon pressureless sintering at 1600 °C. Higher values of the bend strength, up to 855 MPa, were obtained for the post-sintered hipped composites at 1500 °C. The high bend strength and fracture toughness, KIC, result from strong fibre matrix interface. The toughening mechanisms were found to comprise transformation toughening, domain switching and crack deflection toughening. The addition of Al2O3-SF to the matrices of low yttria content was invaluable due to its high monoclinic content upon sintering.