Superplastic ceramics (with emphasis on iron carbide). Final report, 1 May 88-30 Apr 91

Technical Report · Wed Jul 31 04:00:00 EDT 1991

OSTI ID:5474935

Sherby, O D; Wolfenstine, J; Kim, W J

Ultrafine grained iron carbide material was developed by an atomized powder process, utilizing hipping, pressing and extrusion procedures. The material was made superplastic and behaved like other superplastic ceramics. This observation lead to the following conclusions. Superplastic ceramics and metallic alloys exhibit different trends in tensile ductility in the range where the strain-rate-sensitivity exponent, m, is high. The tensile ductility of superplastic metallic alloys (e.g. fine-grained zinc, aluminum, nickel and titanium alloys) is primarily a function of the strain-rate-sensitivity exponent. In contrast, the tensile ductility of superplastic ceramic materials (e.g. zirconia, alumina, zirconia alumina composites and iron carbide) is not only a function of the strain rate sensitivity exponent, but also a function of the parameter where the steady state strain rate and Qc is the activation energy for superplastic flow. Superplastic ceramic materials exhibit a large decrease in tensile elongation with an increase. This trend in tensile elongation is explained based on a 'fracture-mechanics' model. The model predicts that tensile ductility increases with a decrease in flow stress, a decrease in grain size and an increase. The difference in the tensile ductility behavior of superplastic ceramics and metallic alloys can be related to their different failure mechanisms. Superplastic ceramics deform without necking and fail by intergranular cracks that propagate perpendicular to the applied tensile axis. In contrast, superplastic metallic alloys commonly fail by intergranular and transgranular (shearing) mechanisms with associated void formation in the neck region.

• Research Organization: Stanford Univ., CA (United States). Dept. of Materials Science and Engineering
• OSTI ID: 5474935
• Report Number(s): AD-A-246251/3/XAB; CNN: DAAL03-88-K-0056
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360203* -- Ceramics
Cermets
& Refractories-- Mechanical Properties
ACTIVATION ENERGY
ALLOYS
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
ATOMIZATION
CARBIDES
CARBON COMPOUNDS
CERAMICS
CHALCOGENIDES
COMPARATIVE EVALUATIONS
COMPOSITE MATERIALS
CRYSTAL STRUCTURE
DUCTILITY
ELEMENTS
ELONGATION
ENERGY
EVALUATION
EXTRUSION
FABRICATION
GRAIN SIZE
IRON
IRON CARBIDES
IRON COMPOUNDS
MATERIALS
MATERIALS WORKING
MECHANICAL PROPERTIES
METALS
MICROSTRUCTURE
NICKEL
OXIDES
OXYGEN COMPOUNDS
PLASTICITY
POWDERS
SENSITIVITY
SIZE
STRAIN RATE
STRESSES
TENSILE PROPERTIES
TITANIUM ALLOYS
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS
VOIDS
ZIRCONIUM COMPOUNDS
ZIRCONIUM OXIDES