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ZrO 2 /ZrO 2 Layered Composites for Crack Bifurcation
Author(s) -
SánchezHerencia Antonio J.,
Pascual C.,
He Ju,
Lange Fred F.
Publication year - 1999
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.1151-2916.1999.tb01949.x
Subject(s) - materials science , composite material , volume fraction , scanning electron microscope , layer (electronics) , flexural strength , thin film , tetragonal crystal system , monoclinic crystal system , delamination (geology) , crystallography , crystal structure , chemistry , paleontology , biology , subduction , tectonics , nanotechnology
Laminates containing a thin layer (5 to 200 µm thick) sandwiched between two thick layers (2 mm thick) were fabricated by sequential slip casting in order to study crack bifurcation. The thin layer was formed with a mixture of a pure ZrO 2 powder (MZ) and a Zr(Y)O 2 powder containing 3 mol% Y 2 O 3 (TZ). The thick layers were formed with TZ powder containing 0.05 volume fraction of Al 2 O 3 powder to distinguish the interfaces between the different layers in the scanning electron microscope. Dilatometry data for monolithic specimens formed with the mixed MZ and TZ powders (0.30 to 1.00 volume fraction MZ) showed that the monoclinic‐to‐tetragonal transformation temperature and strain varied with the MZ content, suggesting the yttria in the TZ powder diffused into the MZ powder during processing at 1500°C/2 h. These data also showed that large compressive stresses developed in the thin layer due to the transformation. Conditions (thin layer composition and thickness) for observing edge cracks produced along the center line of the thin layer and for observing crack bifurcation during flexural failure were determined. Delamination occurred during cooling for layers fabricated with greaterthan equal to0.40 volume fraction of the MZ powder when the thin layers were 200 µm thick. Edge cracking, which occurred during cooling, and crack bifurcation, which occurred during flexural loading, occurred for thin layer compositions containing greaterthan equal to0.40 volume fraction MZ powder, when the thickness of the thin layer was between similar/congruent50 and 150 µm. Crack bifurcation was not observed in thinner layers. With decreasing layer thickness, thin layers fabricated with >0.60 volume fraction of the MZ powder contained multiple microcracks, parallel to the center line, on the surface, instead of a single edge crack. The flexural strength of all specimens depended on the strength of the thicker Zr(Y)O 2 layers, regardless of whether bifurcation occurred.