Crack stability and strength variability in alumina ceramics with rising toughness-curve behavior

• Published in: Acta materialia Vol. 48; no. 2; pp. 565 - 578
• Main Authors: Kovar, Desiderio, Bennison, Stephen J, Readey, Michael J
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 24-01-2000; Elsevier Science
• Subjects: ALUMINIUM OXIDES; Ceramics; Condensed matter: structure, mechanical and thermal properties; CRACKS; Exact sciences and technology; Fatigue, brittleness, fracture, and cracks; FRACTURE MECHANICS; FRACTURE PROPERTIES; Fracture toughness; GRAIN SIZE; MATERIALS SCIENCE; Mechanical and acoustical properties of condensed matter; Mechanical properties; Mechanical properties of solids; Microstructure; MORPHOLOGY; Physics; R-curve; Mechanical properties; Ceramics; Microstructure; R-curve; Fracture toughness; Grain size; Fracture mechanics; Mechanical strength; Theoretical study; Property structure relationship; SEM; Alumina; Fractography; Tenacity
• ISSN: 1359-6454; 1873-2453
• DOI: 10.1016/S1359-6454(99)00350-X

Aluminas with four distinct microstructures have been fabricated to investigate the influence of grain size and grain morphology on strength variability. The four microstructures comprise two grain size scales and are characterized as either “equiaxed” with a narrow size distribution or “elongate” with a higher aspect ratio and a broader size distribution. Indentation-strength tests indicate that only the coarse-grain, elongate microstructure exhibits a strong rising toughness-curve (
T-curve or
R-curve). Furthermore,
in situ measurements demonstrate that the coarse-grain, elongate microstructure is the only one that displays significant
stable crack extension from annealed indentation flaws free of contact-induced residual stress. Strength tests on polished specimens indicate that the highest mean strength is achieved in the fine-grain, equiaxed material with little or no
T-curve. The lowest strength variability, however, is exhibited by the coarse-grain, elongate alumina and is rationalized in terms of the strong rising
T-curve and its associated influence on crack stability. The study suggests that maximum reliability is achieved when the
T-curve is sufficiently strong to stabilize the propagation of
natural flaws
en route to failure.