Diffusional creep and cavitation of alumina under tensile and hydrostatic stresses

Antai Xu, Purdue University

Abstract

Diffusional creep and cavitation in pure alumina prepared with different fabrication processes are compared under tension and subsequent hydrostatic compression. The deformation rates are separated into continuum creep and cavitational strain by measuring the longitudinal and transverse strain rates. When concurrent grain growth is accounted for, the continuum strain rate decreases in a manner consistent with Nabarro-Herring creep. The creep stress index of n = 1.3 and the activation energy of Q = 480 kJ/mole also indicate control of continuum deformation by aluminum lattice diffusion. The activation energy and stress dependence of the cavitation rate are consistent with a grain boundary diffusional growth mechanism. The cavitation/decavitation rates are in good agreement with the model proposed by Speight and Beere when the effects of grain growth on cavity accumulation on grain boundaries are considered. The loading mode is found to have no significant effect on the cavitation rate during tensile creep and the subsequent decavitation rate during hydrostatic compression. Exaggerated grain growth in high density specimens can lead to early cavity coalescence and failure. High voltage electron microscopy indicates that, for creep in pure alumina, cavities nucleate early at grain edges, the surfaces of these cavities are faceted with negligible curvature and various dihedral angles.

Degree

Ph.D.

Advisors

Solomon, Purdue University.

Subject Area

Materials science|Mechanical engineering|Nuclear physics

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