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Dense single-phase ...
Dense single-phase β-sialon ceramics by glass-encapsulated hot isostatic pressing
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- Ekström, Thommy (author)
- AB Sandvik Hard Materials, Stockholm
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- Käll, Per-Olov (author)
- University of Stockholm
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- Nygren, Mats (author)
- University of Stockholm
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- Olsson, Per-Olof (author)
- University of Stockholm
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(creator_code:org_t)
- 1989
- 1989
- English.
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In: Journal of Materials Science. - 0022-2461. ; 24:5, s. 1853-1861
- Related links:
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https://urn.kb.se/re...
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https://doi.org/10.1...
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Abstract
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- Single phase-sialon ceramics, Si6–z Al z O z N8–z , have been prepared from carefully balanced powder mixtures, also taking account of any excess oxygen in the starting materials. Sintering powder compacts in a nitrogen atmosphere (0.1 MPa) at 1800° C or higher transforms the starting mixture into a-sialon solid solution atz-values up to about 4.3, but the sintered material has an open porosity. Addition of 1 wt% Y2O3 to the starting mix improved the sintering behaviour somewhat and the density of the sintered compacts reached 95% of the theoretical value. By glass-encapsulated hot isostatic pressing at 1825° C, however, sintered materials of virtually theoretical density could be obtained, with or without the 1 wt% Y2O3 addition. These latter samples have been studied by X-ray diffraction and electron microscopy, and their hardness and indentation fracture toughness have been measured. It was found that the maximum extension of the-sialon phase composition at 1825° C and 200 MPa pressure is slightly below 4,z 3.85 and about 4.1 at atmospheric pressure, and that the hexagonal unit cell parameters are linear functions of thez-value. The single-phase-sialon ceramics had no residual glassy grain-boundary phase. The grain shape was equi-axed and the grain size increased from about 1m at lowz-values to 5m at highz-values. At lowz-values the hardness at a 98 N load was 1700 and the fracture toughness 3, whereas an increase inz above 1 caused both the hardness and fracture toughness to decrease significantly. Addition of 1 wt % Y2O3 to the starting mix prior to the HIP-sintering gave rise to a small amount of amorphous intergranular phase, changes in grain size and shape, a clear increase in fracture toughness and a moderate decrease in hardness.
Keyword
- NATURAL SCIENCES
- NATURVETENSKAP
Publication and Content Type
- ref (subject category)
- art (subject category)
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