VICKERS AND KNOOP INDENTATION BEHAVIOR OF CUBIC AND PARTIALLY-STABILIZED ZIRCONIA CRYSTALS

Hardness and fracture toughness of cubic zirconia crystals (CZC) doped with yttria and partially stabilized zirconia crystals (PSZC) doped w ith yttria, terbia and ceria were studied at indentation loads of 0.1- 300 N. MOR and K-1c of these materials were measured under bending con ditions. A maximum hardness value of H-K = 21.2 GPa was obtained for C ZC at a 0.1 N indentation load when a longer diagonal of the Knoop ind enter being directed along [110]. Starting from a 2 N load, PSZC exhib ited lateral cracks and phase transition zones. Radial cracks in Vicke rs indentation tests of Y-Tb-PSZC and Y-Ce-PSZC appeared above 40 N an d 50 N respectively. Such cracks in Knoop indentation tests were obser ved above 300 N. Orientation anisotropy of lateral cracks was noticed in all crystals, radial ones were revealed only in CZC. After grinding off the specimen surfaces, lateral cracks were found to be present un der the impressions. The calculations of fracture toughness K-1c(v) us ing the equation proposed by the authors gave a value corresponding to those materials determined on bending.