Dependence of tetragonal-ZrO2 grain size on the bending strength of Y-TZP ceramics

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Abstract
09-049 Leonardo Queiroz Bueno Campos SANTOS, C.(UERJ); Alves, M.F.(Universidade do Estado do Rio de Janeiro); Ferreira, I.S.(UERJ-FAT); Campos, L.Q.(UERJ-FAT); Moreira, L.P.(Universidade Federal Fluminense); Simba, B.G.(UNESP-FEG); da Silva, P.C.(Universidade Federal Fluminense); Yttrium-stabilized zirconia, Y-TZP, is a polycrystalline ceramic that exhibits excellent fracture resistance as a consequence of a peculiar phase transformation toughening mechanism. Here, metastable tetragonal-ZrO2 grains undergo the propagation of a crack undergoing transformation of phase, becoming monoclinic, producing a volumetric expansion of 3-4vol%, which hinders the continuity of intergranular crack propagation. According to the importance of tetragonal grains in this mechanism, it is important to determine the effect of grain size, on bending strength of this material. In this work, nanoparticled Y-TZP powder was compacted at 200MPa and sintered at different temperatures (1400 ° C-1600 ° C) to obtain different average grain sizes. Relative density was determined by the Archimedes method, indicating that 1470° C-2h was the lowest temperature where full density was obtained. The crystalline phases were identified by X-ray diffraction, microstructures analyzed by SEM, and microstructural aspects were obtained using ImageJ software. The groups of samples (n> 20) with full densification were characterized by their resistance to biaxial flexion, with consequent Weibull statistics. Only tetragonal ZrO2 grains were observed in the X-ray diffraction analysis. The average grain size was found varying from 0.35 ± 0.10 ?m to 1.80 ± 0.15 ?m. The results of biaxial flexural strength indicate that the Y-TZP groups with smaller grain size exhibit flexural strength of 1210 ± 85MPa while the groups with larger grain size exhibit flexural strength of 910 ± 90MPa, representing a considerable reduction of about of 25%.
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