Degree Type

Dissertation

Date of Award

1983

Degree Name

Doctor of Philosophy

Department

Materials Science and Engineering

Abstract

The single-crystalline elastic constants of yttria-stabilized zirconia (YSZ) have been determined over the temperature range 20-700(DEGREES)C by the pulse-echo-overlap technique. Different crystals of YSZ containing 8.1, 11.1, 12.1, 15.5, and 17.9 mol % Y(,2)O(,3) were examined in the present investigation;The compositional dependencies of the three independent constants at room temperature show that, upon increasing Y(,2)O(,3) content, C(,11) decreases, whereas C(,12) and C(,44) increase. This behavior is best understood from the nature of the interatomic forces of interaction in the fluorite structure of YSZ, wherein the most important contributions are the Coulomb forces and the Born-Mayer repulsive forces of the first nearest neighbors;The high Debye temperatures of the YSZ crystals are characteristic of the strong interatomic interactions. In a harmonic approximation, with neglect of any change in force constants, the Debye temperatures of YSZ crystals should be inversely proportional to the square root of the vibrating masses in the lattice. Such proportionality was found valid for the five YSZ crystals of this investigation;All conventional constants show normal negative temperature dependencies except those of the 8.1 mol % Y(,2)O(,3) alloy, which show nonreproducible behaviors at elevated temperatures;Shear anisotropy in YSZ is pronounced and it decreases with increasing Y(,2)O(,3) content but increases with temperature. Extrapolation of longitudinal and shear constants along different crystallographic directions at room temperature indicates elastic isotropy near 40 mol % Y(,2)O(,3) where a number of investigations have established the presence of an ordered phase (Zr(,3)Y(,4)O(,12)) with a rhombohedral symmetry.

DOI

https://doi.org/10.31274/rtd-180813-8583

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Hamdi M. Kandil

Language

en

Proquest ID

AAI8407086

File Format

application/pdf

File Size

82 pages

Included in

Metallurgy Commons

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