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A New Model for Tensile Creep of Silicon Nitride
Author(s) -
Luecke William E.,
Wiederhorn Sheldon M.
Publication year - 1999
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.1151-2916.1999.tb02154.x
Subject(s) - creep , materials science , diffusion creep , cavitation , composite material , ultimate tensile strength , stress (linguistics) , volume fraction , deformation (meteorology) , phase (matter) , silicon nitride , hydrostatic pressure , hydrostatic stress , power law , thermodynamics , microstructure , grain boundary , chemistry , physics , mathematics , linguistics , philosophy , organic chemistry , statistics , layer (electronics) , finite element method
The tensile creep rate of most commercial grades of Si 3 N 4 increases strongly with stress. Although the usual power‐law functions can represent the creep data, the data often show curvature and systematic variations of slope with temperature and stress. In this article, we present a new approach to understanding the creep of ceramics, such as Si 3 N 4 , where a deformable second phase bonds a deformation‐resistant major phase. A review of experimental data suggests that the rate of formation and growth of cavities in the second phase controls creep in these materials. The critical step for deformation is the redistribution of the second phase away from the cavitation site to the surrounding volume. The effective viscosity of the second phase and the density of active cavities determine the creep rate. Assuming that the hydrostatic stresses in pockets of the second phase are normally distributed leads to a model that accurately describes the tensile creep rate of grades of Si 3 N 4 . In this model, the creep rate increases exponentially with the applied stress, is independent of Si 3 N 4 grain size, is inversely proportional to the effective viscosity of the deformable phase, and is proportional to the cube of the volume fraction of the deformable phase.