Processing and characterization of transformation-toughened ceramics with strength retention to elevated temperatures: Final report

Technical Report · Fri Jul 01 00:00:00 EDT 1988

OSTI ID:7061915

Cutler, R A; Hansen, J J; Prouse, D W; Bright, J D; Virkar, A V; Shetty, D K

Al/sub 2/O/sub 3/-ZrO/sub 2/ three layered composites were fabricated in such a way that the outer layers of the bar-shaped specimens consisted of Al/sub 2/O/sub 3/ and unstabilized ZrO/sub 2/, and the inner layer consisted of Al/sub 2/O/sub 3/ and partially-stabilized ZrO/sub 2/. Upon cooling from the sintering temperature, part of the ZrO/sub 2/ in the outer layers transformed from tetragonal (t) to monoclinic (m), while the inside layer ZrO/sub 2/ remained tetragonal. The transformation created compressive stresses in the outer layers and tensile stresses in the bulk. The depth of the outer layers (and therefore the magnitude of the residual stresses) was controlled during green forming. Residual stresses at room temperature varied depending on the outer layer thickness. The increased strengths of the three layer specimens were obtained in the as-fired unground condition, demonstrating that the stresses introduced are the result of transformation-induced stresses during cooling, and did not from transformation produced by grinding. Specimens with residual surface compressive stresses were 200 MPa stronger at 750/degree/C than monolithic specimens, demonstrating the viability of this approach for improving elevated temperature mechanical properties. Strain gauge, x-ray diffraction, and indentation/strength measurements were used to verify the existence of the macroscopic residual stresses. Slip casting and tape casting were investigated as alternative green forming routes to powder pressing. The substitution of HfO/sub 2/ for ZrO/sub 2/ in order to increase the transformation temperature was investigated. 28 refs., 25 figs., 7 tabs.

• Research Organization: Oak Ridge National Lab., TN (USA); Ceramatec, Inc., Salt Lake City, UT (USA)
• DOE Contract Number: AC05-84OR21400
• OSTI ID: 7061915
• Report Number(s): ORNL/Sub-85-22028/1; ON: DE89001312
• Resource Relation: Other Information: Portions of this document are illegible in microfiche products
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM OXIDES
MECHANICAL PROPERTIES
ZIRCONIUM OXIDES
EQUATIONS
FABRICATION
FRACTURE PROPERTIES
HAFNIUM OXIDES
LAYERS
MICROSTRUCTURE
PHASE TRANSFORMATIONS
PHYSICAL PROPERTIES
PROGRESS REPORT
RESIDUAL STRESSES
SINTERING
STRAIN GAGES
X-RAY DIFFRACTION
ALUMINIUM COMPOUNDS
CHALCOGENIDES
COHERENT SCATTERING
CRYSTAL STRUCTURE
DIFFRACTION
DOCUMENT TYPES
HAFNIUM COMPOUNDS
MEASURING INSTRUMENTS
OXIDES
OXYGEN COMPOUNDS
REFRACTORY METAL COMPOUNDS
SCATTERING
STRESSES
TRANSITION ELEMENT COMPOUNDS
ZIRCONIUM COMPOUNDS
360203* - Ceramics
Cermets
& Refractories- Mechanical Properties
360202 - Ceramics
Cermets
& Refractories- Structure & Phase Studies