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Space‐Charge‐Controlled Diffusional Creep: Volume Diffusion Case †
Author(s) -
Jamnik Janez,
Raj Rishi
Publication year - 1996
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1996.tb07898.x
Subject(s) - valency , creep , diffusion , materials science , thermal diffusivity , space charge , thermodynamics , ionic bonding , debye length , diffusion creep , grain size , condensed matter physics , chemical physics , grain boundary , composite material , chemistry , physics , ion , electron , microstructure , philosophy , linguistics , organic chemistry , quantum mechanics
The diffusive flux of atoms required in Nabarro‐Herring creep can, under certain conditions, become limited by diffusion across the space charge layer that is associated with interfaces in ionic or partly ionic materials. We derive a new equation for volume diffusional creep in such materials. Physically speaking, the creep rate is enhanced when the defect, which controls the self‐diffusivity, is accumulated, and retarded when this defect is depleted, in the space charge region. For the enhanced case the factor by which the strain rate is increased quickly reaches a limit given by 1 + 4L D /d , where L D is the Debye length, and d is the grain size. In the other case the retardation factor continues to increase exponentially with the space charge potential: furthermore, the retardation is most severe when the valency of the accumulating defect, which constitutes the space charge region, is small, while the valency of the depleted defect, which controls diffusion, is large. In retardation the grain size dependence of the creep rate changes from d ‐2 to d ‐1 .