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The Effect of Glass Composition on Creep Damage Development in Silicon Nitride Ceramics

Published

Author(s)

F Lofaj, Sheldon M. Wiederhorn, F Dorcakova, Michael J. Hoffmann

Abstract

Creep damage development during tensile creep in two different commercial silicon nitride ceramics, SN88 and SN 281, was measured using precise density measurement and anomalous ultra-small X-ray scattering (A-USAXS) techniques. The study revealed that cavitation at multigrain junctions is the main creep damage type and creep mechanism in SN88 which contains Yb/Y-based additives. However, it was fully suppressed in SN281 containing Lu-based additives. Suppression of cavitation resulted in the increase in creep resistance of almost 4 orders of magnitude and more than 200oC higher operational temperatures in comparison with SN88. The analysis of creep behavior of the studied ceramics suggested that the transformation from cavitation to non-cavitation creep mechanism may be related to the changes in viscosity of the residual glass at the grain boundaries due to the presence of Lu. Subsequent viscosity study on the model bulk lanthanide-containing oxide and oxynitride glasses showed that the replacement of Yb by Lu can increase the glass transition temperature, Tg, maximum by 25-36oC and viscosity increases only by a factor of x 25-100. This is obviously insufficient to explain changes in the creep resistance of SN281. However, the incorporation of nitrogen has independent and considerably stronger effect than lanthanides: adding 24 e/o N in the corresponding oxide increased Tg by 84-100oC and viscosity by a factor of 105. Thus, the suppression of cavitation and significant increase in creep resistance in SN281 can be related to the simultaneous effects of higher degree of cross-linking due to the presence of 3-coordinated N and better packing of glass structure containing Lu modifier with smaller ionic radius on residual glass viscosity. However, the assumption of the same behavior of bulk glasses and 1 nm thin intergranular films with the same composition remains to be justified.
Proceedings Title
International Conference on Fracture | 11th | | International Congress on Fracture
Conference Dates
March 20-25, 2005
Conference Location
Turin, 1, IT
Conference Title
International Congress on Fracture

Keywords

density, glass viscosity, oxynitride glasses, silicon nitride

Citation

Lofaj, F. , Wiederhorn, S. , Dorcakova, F. and Hoffmann, M. (2021), The Effect of Glass Composition on Creep Damage Development in Silicon Nitride Ceramics, International Conference on Fracture | 11th | | International Congress on Fracture, Turin, 1, IT (Accessed April 18, 2024)
Created October 12, 2021