Abstract
The sintering conditions employed in this work are innovative, due to the use of an alternative technology to process ZrO2-REO (rare earth oxide mixture), so called high temperature - high pressure (HPHT). A pressure of 5GPa was used, temperatures of 1100, 1200, and 1300 o C, for times of 2 and 5 minutes. The best results were obtained for samples sintered at 5GPa/1300 o C/5min., where a micro-hardness of 4.8GPa, fracture toughness of 5.3MPa.m ?, density of 97.9%, and 88% in volume of a tetragonal phase retained at room temperature were achieved.
Highlights
The most promising applications of zirconia is as structural ceramicс and as solid electrolytes [1].Pure ZrO2 presents 3 polymorphs at atmospheric pressure: monoclinic – m – from room temperature to 1170oC, tetragonal – t – from 1170 to 2370oC, and cubic – c – from 2370 to 2680oC [2]
Yttria-stabilized zirconia is known to be hard and tough at room temperature, that enables the use of this material, in a tetragonal phase, as an advanced ceramic [3], and prominently in applications as cutting tools
According to fig.1 and tab.II, it is seen that all samples were high pressures and high temperatures (HPHT) sintered into the tetragonal phase stability region
Summary
The most promising applications of zirconia is as structural ceramicс (combustion engine parts, turbine blades, cutting tools, prosthetics, etc) and as solid electrolytes (oxygen and gas sensors, fuel cells, oxygen pump, etc) [1].Pure ZrO2 presents 3 polymorphs at atmospheric pressure: monoclinic – m – from room temperature to 1170oC, tetragonal – t – from 1170 to 2370oC, and cubic – c – from 2370 to 2680oC [2]. Yttria-stabilized zirconia is known to be hard and tough at room temperature, that enables the use of this material, in a tetragonal phase, as an advanced ceramic [3], and prominently in applications as cutting tools. Feder et al [4] and Piconi and Maccauro [5] affirmed that the t-m transformation is of a martensitic nature, which is accompanied by a volumetric expansion (∆V) of 4%. When such a transformation takes place, a tension field is generated at the cracks’ surrounds, due to ∆V, which in turn leads to a fracture toughness (KIc) increase in ZrO2
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