Microstructural tailoring of transformation toughened ceramics

Conference · Tue Jan 01 04:00:00 EST 1991

OSTI ID:6115493

Becher, P F; Alexander, K B; Bleier, A; Westmoreland, C G; Warwick, W H; Waters, S B

The tetragonal-to-monoclinic transformation temperature M{sub s} and the transformation toughening contribution {Delta}K{sup T} increase with increase in grain size of the tetragonal zirconia present in either polycrystalline tetragonal zirconia or zirconia-toughened alumina composites. However, the grain size dependence of both M{sub s} and {Delta}K{sup T} increases with decrease in zirconia content. Thus, the microstructures of such materials must be carefully tailored to optimize their performance. This has been achieved here by employing colloidal processing conditions which promote weak particle-particle interactions in the binary suspension to obtain uniform spatial distribution of both the zirconia and alumina phases and to maintain the initial narrow size distributions by minimizing agglomeration and differential settling. Sintering conditions were then utilized to obtain dense materials of selected grain sizes. However, the grain growth rates are influenced by the degree of interconnectivity of the phases. For example, decreasing the zirconia content results in reducing the zirconia grain rates. Theoretical analysis reveals that the main factor in the grain size dependency of the transformation behavior is the increasing contribution of internal residual tensile stresses, generated by thermal expansion anisotropy/mismatch, with increase in grain size. The observed increase in the dependence of M{sub s} on grain size for Al{sub 2}O{sub 3}-ZrO{sub 2} (12 mol % CeO{sub 2}) composites with increasing alumina content vs that for ZrO{sub 2} (12 mol % CeO{sub 2}) ceramics confirm the role of the internal residual stress contribution in promoting the transformations. The control of the M{sub s} temperature by regulating the zirconia grain size then allows the fracture toughness of each the composites to be optimized.

• Research Organization: Oak Ridge National Lab., TN (United States)
• Sponsoring Organization: DOE; USDOE, Washington, DC (United States)
• DOE Contract Number: AC05-84OR21400
• OSTI ID: 6115493
• Report Number(s): CONF-9110319-1; ON: DE92005433
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360201 -- Ceramics
Cermets
& Refractories-- Preparation & Fabrication
360202* -- Ceramics
Cermets
& Refractories-- Structure & Phase Studies
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
CHALCOGENIDES
CRYSTAL STRUCTURE
FRACTURE PROPERTIES
GRAIN SIZE
HARDNESS
MECHANICAL PROPERTIES
MICROSTRUCTURE
OXIDES
OXYGEN COMPOUNDS
PHASE TRANSFORMATIONS
SIZE
TRANSITION ELEMENT COMPOUNDS
ZIRCONIUM COMPOUNDS
ZIRCONIUM OXIDES