Abstract
The main goal of this work was to obtain dense Al2O3–Y3Al5O12 ceramic composites by reactive sintering of three-dimensional samples, built by direct ink writing from a paste containing a mixture of Al2O3 and Y2O3 powders. To obtain a ceramic ink with proper rheological properties for extrusion-based printing, highly pure Al2O3 and Y2O3 powders in a percentage–weight ratio of 64:36 was mixed with 0.2 wt% MgO in a total solid loading of 42 vol% in aqueous media, adding carboxymethyl cellulose and polyethyleneimine solution as additives. The dried printed samples were sintered at final temperatures in the range of 1550 °C and 1650 °C; thus, relative densities of 83.7 ± 0.8%, 95.4 ± 0.4%, and 96.5 ± 0.5% were obtained for 1550 °C, 1600 °C, and 1650 °C, respectively. Rietveld refinement performed on the X-ray diffraction patterns indicated the presence of Al2O3 (42 to 47%) and Y3Al15O12 (58 to 61%) as crystalline phases, while micrographs showed the presence of equiaxial micrometric grains with average sizes of 1.8 ± 0.6 μm, for both phases and all sintering conditions. Samples sintered at 1600 °C and 1650 °C presented similar average Vickers hardness values of 14.2 ± 0.27 GPa and 14.5 ± 0.25 GPa, respectively. A slight increase in fracture toughness as sintering temperature increases was also stated, consistent with the densification.
Highlights
Alumina-based ceramics have been used for several decades in structural applications, due to their excellent dimensional integrity and stability at high temperatures, intrinsic corrosion resistance from their strong ionic chemical bonds, high hardness, and, high wear resistance [1,2,3]
In the case of Al2O3 and yttria-stabilized zirconia Y-TZP, zirconia-toughened alumina (ZTA) or alumina-reinforced zirconia ceramics (ATZ, aluminatoughened zirconia) could be attained depending on their proportions [7,8]. In another type of composites, constituent materials can chemically react at elevated temperatures in a process of phases transformation “in situ”, called “reactive sintering” [9,10], resulting in different crystalline phases after sintering, as, for example, in the binary ceramic system Al2O3–Y3O2, where crystalline phases, such as YAG (Y3Al15O12), YAP (YAlO3), or YAM (Y4Al12O9), can be formed
The objective of this work was to develop and characterize ceramic composites fabricated by direct ink writing, resultant from aqueous based inks comprising a mixture of Y2O3 and Al2O3 powders, using CMC and PEI as organic additives
Summary
Alumina-based ceramics have been used for several decades in structural applications, due to their excellent dimensional integrity and stability at high temperatures, intrinsic corrosion resistance from their strong ionic chemical bonds, high hardness, and, high wear resistance [1,2,3]. In the case of Al2O3 and yttria-stabilized zirconia Y-TZP (composites), zirconia-toughened alumina (ZTA) or alumina-reinforced zirconia ceramics (ATZ, aluminatoughened zirconia) could be attained depending on their proportions [7,8]. In another type of composites, constituent materials can chemically react at elevated temperatures in a process of phases transformation “in situ”, called “reactive sintering” [9,10], resulting in different crystalline phases after sintering, as, for example, in the binary ceramic system Al2O3–Y3O2, where crystalline phases, such as YAG (Y3Al15O12), YAP (YAlO3), or YAM (Y4Al12O9), can be formed. The new phases formed depend on the composition used as well as on the sintering temperature, inducing changes in the chemical and physical properties of the final material
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