Precipitation in alumina-rich spinel: A transformation-toughened ceramic single crystal

Technical Report · Wed Jul 01 00:00:00 EDT 1987

OSTI ID:6017073

Jantzen, C M; Herman, H

The transformation of single crystal spinel supersaturated with alumina to stable ..cap alpha..-Al/sub 2/O/sub 3/ occurs sequentially. Four metastable phases were identified in six unique phase assemblages. The appearance of a more stable decomposition product caused the reversion (dissolution) of its immediate precursor. The two early transient precipitates, I/sub P/ and II/sub P/, were identified as solute rich GP zones aligned along the same crystallographic orientations as the sequentially formed intermediate transition phases, I/sub T/ and II/sub T/. The activation energies for precipitation and reversion were measured to be approx.80 kJ, comparable to activation energies for precipitate strengthening in other ceramic and metallic systems. The phase assemblages are represented in the context of a time-temperature-extent of transformation (TTT) diagram compiled from the work of four independent studies. The phase transformations delineated by the c-shaped rate curves on the TTT diagram are shown to correlate with measured changes in mechanical properties. 58 refs., 12 figs., 2 tabs.

• Research Organization: Savannah River Lab., Aiken, SC (USA); State Univ. of New York, Stony Brook (USA). Dept. of Materials Science
• DOE Contract Number: AC09-76SR00001
• OSTI ID: 6017073
• Report Number(s): DP-MS-87-33; CONF-810528-19; CONF-850536-14; ON: DE87012380
• Resource Relation: Conference: 83. American Ceramic Society symposium on nucleation and crystallization in glasses, Washington, DC, USA, 3 May 1981; 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
PHASE TRANSFORMATIONS
PRECIPITATION HARDENING
MAGNESIUM OXIDES
SPINELS
ACTIVATION ENERGY
BIBLIOGRAPHIES
CERAMICS
GRAIN ORIENTATION
HIGH TEMPERATURE
IMAGES
LATTICE PARAMETERS
MECHANICAL PROPERTIES
METASTABLE STATES
MONOCRYSTALS
QUENCHING
TEMPERATURE EFFECTS
TRANSMISSION ELECTRON MICROSCOPY
VERY HIGH TEMPERATURE
X-RAY DIFFRACTION
ALKALINE EARTH METAL COMPOUNDS
ALUMINIUM COMPOUNDS
CHALCOGENIDES
COHERENT SCATTERING
CRYSTAL STRUCTURE
CRYSTALS
DIFFRACTION
DOCUMENT TYPES
ELECTRON MICROSCOPY
ENERGY
ENERGY LEVELS
EXCITED STATES
HARDENING
MAGNESIUM COMPOUNDS
MICROSCOPY
MICROSTRUCTURE
MINERALS
ORIENTATION
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
SCATTERING
360202* - Ceramics
Cermets
& Refractories- Structure & Phase Studies