Design, microstructure, and high-temperature behavior of silicon nitride sintered with rate-earth oxides

Technical Report · Thu Aug 01 00:00:00 EDT 1991

DOI:https://doi.org/10.2172/5206386· OSTI ID:5206386

Ciniculk, M K ^[1]

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1. California Univ., Berkeley, CA (United States). Dept. of Materials Science and Mineral Engineering

The processing-microstructure-property relations of silicon nitride ceramics sintered with rare-earth oxide additives have been investigated with the aim of improving their high-temperature behavior. The additions of the oxides of Y, Sm, Gd, Dy, Er, or Yb were compositionally controlled to tailor the intergranular phase. The resulting microstructure consisted of {beta}-Si{sub 3}N{sub 4} grains and a crystalline secondary phase of RE{sub 2}Si{sub 2}O{sub 7}, with a thin residual amorphous phase present at grain boundaries. The lanthanide oxides were found to be as effective as Y{sub 2}O{sub 3} in densifying Si{sub 3}N{sub 4}, resulting in identical microstructures. The crystallization behavior of all six disilicates was similar, characterized by a limited nucleation and rapid growth mechanism resulting in large single crystals. Complete crystallization of the intergranular phase was obtained with the exception of a residual amorphous, observed at interfaces and believed to be rich in impurities, the cause of incomplete devitrification. The low resistance to oxidation of these materials was attributed to the minimization of amorphous phases via devitrification to disilicates, compatible with SiO{sub 2}, the oxidation product of Si{sub 3}N{sub 4}. The strength retention of these materials at 1300{degrees}C was found to be between 80% and 91% of room-temperature strength, due to crystallization of the secondary phase and a residual but refractory amorphous grain-boundary phase. The creep behavior was found to be strongly dependent on residual amorphous phase viscosity as well as on the oxidation behavior, as evidenced by the nonsteady-state creep rates of all materials. 122 refs., 51 figs., 12 tabs.

• Research Organization: Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: USDOE; USDOE, Washington, DC (United States)
• DOE Contract Number: AC03-76SF00098
• OSTI ID: 5206386
• Report Number(s): LBL-31223; ON: DE92000815; CNN: DMR 83-1317239
• Resource Relation: Other Information: Thesis (Ph.D.)
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
SILICON NITRIDES
MECHANICAL PROPERTIES
MICROSTRUCTURE
CREEP
CRYSTALLIZATION
DEFORMATION
FRACTURE PROPERTIES
GRAIN BOUNDARIES
MORPHOLOGY
OXIDATION
OXIDES
RARE EARTH COMPOUNDS
SINTERING
TRANSMISSION ELECTRON MICROSCOPY
CHALCOGENIDES
CHEMICAL REACTIONS
CRYSTAL STRUCTURE
ELECTRON MICROSCOPY
FABRICATION
MICROSCOPY
NITRIDES
NITROGEN COMPOUNDS
OXYGEN COMPOUNDS
PHASE TRANSFORMATIONS
PNICTIDES
SILICON COMPOUNDS
360203* - Ceramics
Cermets
& Refractories- Mechanical Properties
360202 - Ceramics
Cermets
& Refractories- Structure & Phase Studies
360201 - Ceramics
Cermets
& Refractories- Preparation & Fabrication