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Comparison of Mechanical Properties of Conventionally and Non-Conventionally Sintered Cold Isostatically Pressed Al2O3 Ceramics

The objective of this study was to investigate and compare the morphology and mechanical properties of cold isostatically pressed (CIP) alumina (Al2O3) samples sintered by conventional (electrical) and non-conventional (hybrid microwave) techniques. Scanning electron microscopy (SEM) was used to examine the morphology of the Al2O3 ceramics sintered by both sintering techniques. Following mechanical properties of CIP alumina ceramics were analysed: (i) Vickers hardness, (ii) Vickers indentation fracture toughness (VIF), (iii) the indentation size effect (ISE) using Vickers method, and (iv) the brittleness index. The ISE is analysed using (i) the Meyer’s law, (ii) the proportional specimen resistance (PSR) model, and (iii) the modified proportional specimen resistance (MPSR) model. It was found that alumina samples sintered in the electric kiln obtained higher density and lower porosity compared to the samples sintered in the hybrid- microwave kiln. The obtained values of the Meyer’s index n are less than 2 for alumina ceramics sintered by both sintering methods, which indicates that the hardness is dependent on the test load. High correlation coefficients confirm that all applied mathematical models are suitable. However, true Vickers hardness obtained by the PSR model was found to be nearer to the measured Vickers hardness of alumina samples regardless of the sintering method applied. Furthermore, it was found that the fracture toughness was higher for alumina ceramics sintered in the hybrid microwave kiln (MK-Al2O3) than the one sintered in the electric kiln (EK-Al2O3). In contrary, the brittleness index was found to be higher for alumina ceramics sintered in the electric kiln (EK-Al2O3) than in the hybrid microwave kiln (MK-Al2O3). Both Vickers hardness and brittleness index values might be correlated to the microstructure of the sintered samples, e.g. finer for non-conventionally sintered alumina.

alumina ceramics ; sintering ; mechanical properties

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