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Strengthening of Oxide Ceramics by Transformation‐Induced Stress
Author(s) -
VIRKAR ANIL V.,
HUANG JOW LAY,
CUTLER RAYMOND A.
Publication year - 1987
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.1151-2916.1987.tb04952.x
Subject(s) - materials science , composite material , cubic zirconia , sintering , scanning electron microscope , tetragonal crystal system , ceramic , ultimate tensile strength , compressive strength , layer (electronics) , stress (linguistics) , flexural strength , oxide , metallurgy , phase (matter) , linguistics , chemistry , philosophy , organic chemistry
Alumina‐zirconia composites were fabricated by isostatic pressing and sintering of powder mixtures in such a way that bar‐shaped specimens consisted of three layers. The outer layers contained A1 2 O 3 and unstabilized ZrO 2 while the central layer contained A1 2 O 3 and partially stabilized ZrO 2 (with 2 mol% Y 2 O 3 ). When cooled from the sintering temperature, some of the zirconia in the outer layers transformed to the monoclinic form while zirconia in the central layer was retained in the tetragonal form. The transformation of zirconia in the outer layers led to the establishment of surface compressive stresses and balancing tensile stresses in the bulk. The existence of surface compressive stresses was verified by a strain gauge technique and bending strength measurements on samples with varying thickness of the outer layers. The layered composites exhibited greater strength in comparison with monolithic Al 2 O 3 ‐ZrO 2 specimens. Further, variation of strength in bending with outer layer thickness (for a fixed total thickness) indicated that failure occurred from internal flaws. Scanning electron microscopy of fracture surfaces revealed that strength‐limiting flaws were voids located in the central layer near the interface separating the central and the outer layers.