Fracture toughness of Al/sub 2/O/sub 3/-ZrO/sub 2/ composites

Conference · Thu Jan 01 00:00:00 EST 1981

OSTI ID:6346173

Becher, P F; Tennery, V J

K/sub IC/ of Al/sub 2/O/sub 3/-ZrO/sub 2/ two-phase ceramic composites was determined for different ZrO/sub 2//Al/sub 2/O/sub 3/ ratios and selected Y/sub 2/O/sub 3/ stabilizer concentrations in the ZrO/sub 2/. The double cantilver beam (DCB) specimen geometry was used. In composites containing 20 vol % ZrO/sub 2/, K/sub IC/ increases (4.6 to 8.5 MPa m/sup 1/2/) with decrease in Y/sub 2/O/sub 3/ content from 3 to 1 mol %. On the other hand, composites containing 30 vol % ZrO/sub 2/, decreasing Y/sub 2/O/sub 3/ additions from 3 to 2 mol % leads to a maximum in K/sub IC/ value of about 6.2 MPa m/sup 1/2/ which occurred in a composition containing 2 mol % Y/sub 2/O/sub 3/. In this same composite, this maximum shifts to a value of about 8 MPa m/sup 1/2/ at about 2 to 3 mol % Y/sub 2/O/sub 3/ at -195/sup 0/C. These observations are consistent with a transformation toughening model wherein an increase in toughness occurs with decrease in Y/sub 2/O/sub 3/ content due to a decrease in the chemical free energy required for the transformation of tetragonal ZrO/sub 2/ to the monoclinic form. The K/sub IC/ also exhibits a maximum with the concentration of ZrO/sub 2/ particles and this maximum in K/sub IC/ increases in value and shifts to higher ZrO/sub 2/ contents wih Y/sub 2/O/sub 3/ stabilizer concentrations of 2 mol %. The increase in K/sub IC/ with ZrO/sub 2/ content results from the resultant increase in the number of ZrO/sub 2/ particles which transform to the monoclinic phase during crack propagation. Microstructural analyses indicate the preexisting extended microcracks are produced along the alumina grain boundaries when larger ZrO/sub 2/ particles at the boundaries transform to the monoclinic phase during cooling subsequent to densification. Such extended microcracking results in a reduction of toughening when linking of microcracks occurs. Microcracks also form at the intersection of ZrO/sub 2/ transformation twins within the particles and the ZrO/sub 2/ particle interface with other ZrO/sub 2/ grains or Al/sub 2/O/sub 3/ grains.

• Research Organization: Oak Ridge National Lab., TN (USA)
• DOE Contract Number: W-7405-ENG-26
• OSTI ID: 6346173
• Report Number(s): CONF-810746-1; ON: DE81028575
• Resource Relation: Conference: International symposium on the fracture mechanics of ceramics, University Park, PA, USA, 15 Jul 1981
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM OXIDES
FRACTURE PROPERTIES
YTTRIUM OXIDES
ZIRCONIUM OXIDES
CHEMICAL COMPOSITION
COMPOSITE MATERIALS
CRACK PROPAGATION
MICROSTRUCTURE
MIXTURES
PHASE TRANSFORMATIONS
ALUMINIUM COMPOUNDS
CHALCOGENIDES
CRYSTAL STRUCTURE
DISPERSIONS
MATERIALS
MECHANICAL PROPERTIES
OXIDES
OXYGEN COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
YTTRIUM COMPOUNDS
ZIRCONIUM COMPOUNDS
360203* - Ceramics
Cermets
& Refractories- Mechanical Properties