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Effect of Interface Properties on Microcracking of Iron Titanate

Published

Author(s)

A Saigal, Stephen A. Langer, W Carter, M H. Zimmerman, K T. Faber, Lin-Sien H. Lum

Abstract

It has been shown both experimentally and theoretically that mechanical properties are strongly dependent on the grain size in single-phase polycrystalline ceramics with large thermal expansion anisotropy [1,2]. This dependence is related to the residual stresses generated from thermal mismatch strains that are created during cooling from the fabrication temperature to room temperature. The mismatch strains are a result of neighboring grains having different crystallographic orientations. These strains can lead to spontaneous cracking. Several equations describing the dependence of grain size on the tendency towards spontaneous cracking have been developed and can be summarized by the following equation:Ic = kγgb/E(δαδT)2 (1) where Ic is the critical facet size above which spontaneous microcracking occurs, k is a model dependent constant. Γgb is the grain boundary surface energy, E is the Young's modulus, δα is the maximumthermal expansion anisotropy and δT is the difference between the stress-free temperature and the temperature of interest (typically room temperature) (3). Maximum thermal expansion anisotropy occurs between grains sharing facets, when the facet-normals are crystallographically oriented such that one is parallel to the direction of maximum thermal expansion and the other is parallel to the direction of minimum thermal expansion. In order to control the spontaneous microcracking and the mechanical properties of these types of materials one would need to control both the grain size and the thermal expansion mismatch. Control of grain size can be achieved during fabrication. One way to control the effective thermal expansion mismatch of the material, and hence, the propensity for spontaneous cracking, is through crystallographic texturing. Texturing can be achieved using conventional processing techniques for ceramics such as slip casting and extrusion, or polarizing ferroelectric or ferromagnetic materials, or magnetically-assisted grain alignment during sample fabrication. The last approach relies on the anisotropy in magnetic susceptibility of paramagnetic ceramics.
Citation
Scripta Metallurgica Et Materialia
Volume
38
Issue
No. 9

Keywords

finite element analysis, iron titanate, microcracking, pseudobrookites, simulations, texture, thermal expansion anisotropy

Citation

Saigal, A. , Langer, S. , Carter, W. , Zimmerman, M. , Faber, K. and Lum, L. (1998), Effect of Interface Properties on Microcracking of Iron Titanate, Scripta Metallurgica Et Materialia (Accessed February 27, 2024)
Created December 31, 1997, Updated October 12, 2021