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Influence of ZrO 2 Grain Size and Content on the Transformation Response in the Al 2 O 3 ─ZrO 2 (12 mol% CeO 2 ) System
Author(s) -
Becher Paul F.,
Alexander Kathleen B.,
Bleier Alan,
Waters Shirley B.,
Warwick Wilbur H.
Publication year - 1993
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.1151-2916.1993.tb03656.x
Subject(s) - grain size , materials science , cubic zirconia , tetragonal crystal system , monoclinic crystal system , grain growth , thermal expansion , toughness , composite material , mineralogy , crystallography , crystal structure , ceramic , chemistry
Based on experimental and modeling studies, the rate of increase in the martensite start temperature M s for the tetragonal‐to‐monoclinic transformation with increase in zirconia grain size is found to rise with decrease in ZrO 2 content in the zirconia‐toughened alumina ZTA system. The observed grain size dependence of M s can be related to the thermal expansion mismatch tensile (internal) stresses which increase with decrease in zirconia content. The result is that finer zirconia grain sizes are required to retain the tetragonal phase as less zirconia is incorporated into the alumina, in agreement with the experimental observations. At the same time, both the predicted and observed applied stress required to induce the transformation are reduced with increase in the ZrO 2 grain size. In addition, the transformation‐toughening contribution at temperature T increases with increase in the M s temperature brought about by the increase in the ZrO 2 grain size, when T > M s . In alumina containing 20 vol% ZrO 2 (12 mol% CeO 2 ), a toughness of ∼10 MPa. √m can be achieved for a ZrO 2 grain size of ∼2 μm ( M s ∼ 225 K). However, at a grain size of ∼2 μm, the alumina–40 vol% ZrO 2 (12 mol% CeO 2 ) has a toughness of only 8.5 MPa. √m ( M s ∼ 150 K) but reaches 12.3 MPa. ∼m ( M s ∼ 260 K) at a grain size of ∼3 μm. These findings show that composition (and matrix properties) play critical roles in determining the ZrO 2 grain size to optimize the transformation toughening in ZrO 2 ‐toughened ceramics.