Recovery of Tetragonal Phase from Previously Transformed Y-TZP

Abstract

ZrO 2 (Y 2 O 3 )-based ceramics are widely used as biomaterials due to high fracture toughness, resulting from the tetragonal-monoclinic phase transformation in which the ceramic is submitted during crack propagation. In this context, studies involving the possibility of optimization of the tetragonal phase are important for the properties improvement of this ceramic. This study investigated the recovery of tetragonal phase from a previously transformed ZrO 2 (3 mol% Y 2 O 3 ) ceramic. Zirconia samples were sintered at 1450 °C, at 1530 °C -2 h and at 1600 °C -4 h, in order to obtain materials with distinct microstructural features. The sintered samples were characterized by relative density, X-ray diffraction and scanning electron microscopy. Samples sintered at 1450 °C, 1530 °C -2 h and 1600 °C -4 h, presented relative densities of 94.2, 99.6 and 99.7% with grains size averages of 0.28, 0.49 and 1.31 μm, respectively. All samples were submitted to milling to induce the tetragonal→monoclinic phase transformation presenting 5, 50 and 65 vol% of monoclinic phase. Subsequently, heat treatments between 400 °C and 1200 °C were conducted to retransform monoclinic in tetragonal phase. It has been found that the smaller the grain size after sintering, the lower the necessary annealing temperatures for fully recovering of tetragonal phase. Annealing temperatures of 950, 1100 and 1200 °C were sufficient to recover almost fully the tetragonal phase.

Experimental analysis and finite element modeling of the piston-on-three balls testing of Y-TZP ceramic

“…As the specimens were sintered in a biphasic region (ZrO 2 -tetragonal+ZrO 2 -cubic) and both structures are remarkably difficult to be distinguished, all the refinements were conducted employing the methodology proposed in [15] The sintered specimens were ground and thoroughly polished using a sequence 9g6g1 µm diamond suspensions after sintering. After polishing, all specimens (discs) were heat-treated at 1250 °C/30 min to recover the tetragonal-ZrO 2 phase previously transformed to monoclinic ZrO 2 during polishing step [16]. The specimens were cleaned with acetone and then in isopropyl alcohol in an ultrasonic bath for 10 min.…”

Caracterização Das Propriedades Mecânicas De Zircônias Policristalinas Tetragonais Estabilizadas Com Ítria

“…Porém, a transformação de fase tetragonal para monoclínica (t-ZrO2 -> m-ZrO2) envolve uma considerável expansão volumétrica (~4%) que é fortemente anisotrópica, com mudanças abruptas nos parâmetros de rede, provocando grandes variações na estrutura cristalina. (Cain, 1990), (Samis, 1995), (Rendtorff, 2009), (Umeri, 2010), (Gallino, Valentin, & Pacchioni, 2011), (Simba, et al, 2016) Uma liga de zircônia com vários tipos de solutos como MgO, CaO, Y2O3 ou CeO2, dependendo do seu tratamento térmico e da sua composição, pode apresentar a estabilidade de polimorfismo afetada, resultando em materiais multifásicos. A ocorrência de uma fase ou fases com simetria ortorrômbica em ligas ZrO2 e ZrO puras foi relatada em algumas ocasiões.…”