CENTRIFUGAL CASTING FOR TH E PRODU C TI ON OF RELIABLE, HIGH STRENGTH CE RAMICS to be published in Proc. 8th CTMTEC. Florence (Italy), 29.6.-4. 7.1994 Willem HUISMAN, Thomas GRAULE and Ludwig J. GAUCKLER, Nonmetallic Material s, Swiss Federal Institute of Technology (ETH), Sonneggstr. 5, 8092 Zurich, Switzerland Alumina and zirconia toughened alumina (ZTA) ceramic parts were produced via centrifugal casting. Deagglomerated slurries with up to 57 vol% solids content were cast to compacts of up to 8 cm height. High green and high sintered densities %TD) were reached at low sintering temperatures. Differential sedimentation during centrifugation was negligible for slurries with high solids loadings, even in the ZTA system. Homogeneous distributions of zirconia in alumina matrices were produced (ZTA} by the addition of an organic surfactant leading to homogeneous and fine microstructures. For a-alumina 4-point-bending tests showed an average strength of 540 MPa with a Weibull modulus of 24. 1. INTRODUCTION Despite the many advantages (hardness, wear and corrosion resistance) which many ceramics provide, the principle disadvantage to a- wider range of applications is their lack of reliablity. Although high strength can be displayed the principally brittle mode of fracture sometimes results in sudden and complete failure of a component. According to Griffith's equation, the strength of ceramic components can be increased by either minimizing the flaw size, or by augmenting the fracture toughness, Kie· By decreasing the critical flaw size the size distribution will get narrower as well and thus an increase in reliability can be expected. For non toughened ceramics like alumina this is the only way to enhanced reliability un less toughening phases like zirconia, whiskers, fibers or platelets are added. Higher fracture toughness values can be obtained by utilizing the martensitic phase transformation of tetragonal to monoclinic Zr02. From the group of zirconia toughened ceramics (ZTC}, TZP (tetragonal zirconia polycrystal s) and ZTA (zirconia toughened alumina) are the most well known. TZP exhibits both, small grain size (< 1 μm), as well as, transformation toughening with K1 c's up to 11 MPa..Jm. The increased fracture toughness of the binary ZTA system strongly depends on the size and distribution of the zirconia particles in the alumina mat rix, which are critically influenced by processing. Advances in Science and Technology, 3C, Ceramics: Charting the Future, P. Vincenzini (Ed.), Techna Srl., Florence, Italy, (1995), 1593-1600