Evaluation of Hardness and Fracture Toughness of TZP Ceramics Stabilized with Yttria Concentrates

Abstract

The influence of yttria purity level on hardness and fracture toughness of TZP ceramics was investigated. Terbium, dysprosium, holmium, erbium and ytterbium were the heavy rare earths evaluated as impurities. Samples were prepared employing zirconia powders doped with 3 mol% of high purity yttria or concentrates containing 85 and 95 wt% of this oxide. Two procedures were used to obtain the concentrates: solvent extraction and mixture of purified heavy rare earth oxides. These powders were synthesized by the coprecipitation route, pressed by uniaxial compaction (100 MPa) and sintered at 1500 °C for 1 hour. Gas adsorption (BET), laser diffraction and scanning electron microscopy were the techniques used for powder characterization. The sintered pellets were characterized by X-ray diffraction and scanning electron microscopy. Apparent density values were determined by the Archimedes method. Hardness and fracture toughness were evaluated by Vickers indentation technique. It was verified that the presence of heavy rare earth oxides in yttria concentrates has no significant effect on mechanical properties of zirconia ceramics. These samples have uniform microstructure, composed by tetragonal grains smaller than 0.5 μm. Hardness and fracture toughness are around 13 GPa and 6 MPa.m 1/2 , respectively.