Abstract
The substance 3 mol% yttria stabilized zirconia (3Y-TZP) has become a commodity for the manufacture of components in biomedical and engineering applications. Materials made from stabilizer-coated rather than co-precipitated starting powders are known for their superior toughness and low temperature ageing resistance. The reason for this phenomenon is however still not fully understood. In this study, 3Y-TZP materials hot pressed at 1300–1450 °C for 1 h were characterized. It was found that at a sintering temperature of 1375 °C, a transition from fine grain to coarse grain microstructure associated with a shift from tough and ageing resistant to brittle and prone to ageing was observed. The detailed analysis of the phase composition by X-ray diffraction revealed that TZPs consists of up to five crystallographically different phases of zirconia simultaneously whose contents dynamically change with sintering temperature. At low sintering temperature, the predominant phases are a tetragonal phase with low yttria content and large domain size and high tetragonality together with a cubic phase of high yttria content. At high temperature, a tetragonal phase of higher yttria content and lower tetragonality is formed together with a cubic phase of lower yttria content.
Highlights
The detailed analysis of the phase composition by X-ray diffraction revealed that TZPs consists of up to five crystallographically different phases of zirconia simultaneously whose contents dynamically change with sintering temperature
The excellent mechanical properties of partially stabilized zirconia materials is based on an effect called “transformation toughening” which describes the stress induced martensitic transformation of metastable tetragonal phase associated with volume expansion and shear
X-ray diffraction (XRD) measurements have shown that the transition in mechanical properties, microstructure and ageing characteristics of 3Y-TZP manufactured from stabilizer coated powder can be traced back to a change in the phase composition of the materials with increasing time and temperature
Summary
The excellent mechanical properties of partially stabilized zirconia materials is based on an effect called “transformation toughening” which describes the stress induced martensitic transformation of metastable tetragonal phase associated with volume expansion and shear. Tetragonal zirconia forced into a sevenfold coordination by stabilization with yttria returns into the unfavorable eight-fold coordination (presenting a size mismatch at ambient temperature) and transforms spontaneously to monoclinic; an effect which can cause severe difficulties in biomedical applications by spallation or even complete disintegration of implants in vivo [10,11]. The current study aims at elucidation of what happens in detail at which temperature and in which sequence For this purpose materials were made by hot pressing at relatively low sintering temperatures and short dwell to obtain materials that are fully dense ( different elastic constraint cannot effect phase composition) and to be able to monitor the stabilizer distribution in the early stage by XRD. A complete characterization of mechanical properties, microstructure and low temperature degradation behavior is included in order to be able to correlate the phase changes to macroscopically measurable and technically relevant properties based on a uniform set of data
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