Compressive creep behavior of hot-pressed Si{sub 3}N{sub 4}-CRE{sub 2}O{sub 3}-Al{sub 2}O{sub 3} ceramics

In this work, yttrium-rare earth oxide solid solution, CRE{sub 2}O{sub 3}, produced at FAENQUIL-DEMAR at a cost of only 20% of pure commercial Y{sub 2}O{sub 3}, was used as sintering additive of hot-pressed Si{sub 3}N{sub 4} ceramics. The objective of this work was to characterize and to investigate...

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Published inMaterials research bulletin Vol. 39; no. 9
Main Authors Santos, C., Strecker, K., Barboza, M.R.J., Neto, F. Piorino, Silva, O.M.M., Silva, C.R.M. da
Format Journal Article
LanguageEnglish
Published United States 02.07.2004
Subjects
ACTIVATION ENERGY
ALUMINIUM OXIDES
CERAMICS
CREEP
DOPED MATERIALS
GRAIN BOUNDARIES
GRAIN GROWTH
HOT PRESSING
MATERIALS SCIENCE
RARE EARTHS
SCANNING ELECTRON MICROSCOPY
SILICON NITRIDES
SINTERING
SOLID SOLUTIONS
SOLUTION HEAT
STRESSES
VISCOUS FLOW
X-RAY DIFFRACTION
YTTRIUM
YTTRIUM OXIDES
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Summary:In this work, yttrium-rare earth oxide solid solution, CRE{sub 2}O{sub 3}, produced at FAENQUIL-DEMAR at a cost of only 20% of pure commercial Y{sub 2}O{sub 3}, was used as sintering additive of hot-pressed Si{sub 3}N{sub 4} ceramics. The objective of this work was to characterize and to investigate the creep behavior of these ceramics. The samples were sintered by hot-pressing at 1750 deg. C, for 30 min using a pressure of 20 MPa. Compressive creep tests were carried out in air, between 1250 and 1300 deg. C, for 60 h, under stresses of 200-300 MPa. The stress exponent under all conditions was determined to be about unity. The apparent activation energy obtained was around 460 kJ mol{sup -1}, corresponding to the heat of solution of the Si{sub 3}N{sub 4} in the glassy phase. Both the stress exponent n and apparent activation energy Q are within the range of values reported in other studies of the compressive creep of Y{sub 2}O{sub 3}-Al{sub 2}O{sub 3}-doped-Si{sub 3}N{sub 4} ceramics. X-ray diffraction (XRD) characterization shows a global reorientation of the {beta}-Si{sub 3}N{sub 4} grains and SEM observations detected no grain growth after the creep tests. These results indicate that grain-boundary sliding controlled by viscous flow is the dominant creep mechanism observed in the present study. The creep resistance presented of this samples indicates that this additive CRE{sub 2}O{sub 3} can be a cheap alternative in the fabrication of Si{sub 3}N{sub 4} ceramics, resulting in promising mechanical properties.
ISSN:0025-5408
1873-4227
DOI:10.1016/j.materresbull.2004.04.006