Deformation and microstructural changes in SiC whisker-reinforced Si sub 3 N sub 4 composites

Journal Article · Sun Dec 01 00:00:00 EST 1991 · Journal of Materials Research; (United States)

DOI:https://doi.org/10.1557/JMR.1991.2735· OSTI ID:5525551

Koester, D A ^[1]; More, K L ^[2]; Davis, R F ^[1]

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1. Department of Materials Science and Engineering, North Carolina State University, Box 7907, Raleigh, North Carolina 27695-7907 (United States)
2. High Temperature Materials Laboratory, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6064 (United States)

Constant stress compressive creep studies have been conducted on hot-pressed Si{sub 3}N{sub 4} containing 30 vol. % SiC whiskers and an initial vitreous phase composed of Al{sub 2}O{sub 3}, Y{sub 2}O{sub 3}, and SiO{sub 2}. The conditions of temperature and stress were 1470--1670 K and 50--350 MPa, respectively; the atmosphere was purified N{sub 2} at 1 atm. Significant changes in the stress exponent and activation energy indicate a change in the controlling creep mechanism at {approx}225 MPa and 1570 K. Prolonged annealing in the unstressed condition reduced creep rates but had little effect on the stress exponent values. Transmission and scanning electron microscopy revealed that the break in the stress exponent curves was caused by the removal of the amorphous material at the grain boundary and resulting contacts between Si{sub 3}N{sub 4} grains. The break in the activation energy curves is believed to be similarly related. Analysis of all the data indicates that the composite creeps via grain boundary sliding accommodated by viscous flow at low stresses and temperatures and by diffusion at high stresses and temperatures. The contributions of these two mechanisms varied measurably as a function of stress and temperature. No cavitation was observed. The presence of the SiC whiskers had no observable effect on deformation.

• DOE Contract Number: AC05-84OR21400
• OSTI ID: 5525551
• Journal Information: Journal of Materials Research; (United States), Vol. 6:12; ISSN 0884-2914
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
COMPOSITE MATERIALS
CREEP
MICROSTRUCTURE
SILICON CARBIDES
SILICON NITRIDES
ACTIVATION ENERGY
ANNEALING
DEFORMATION
ELECTRON MICROSCOPY
HOT PRESSING
STRESSES
TEMPERATURE DEPENDENCE
TEMPERATURE RANGE 1000-4000 K
VERY HIGH PRESSURE
WHISKERS
CARBIDES
CARBON COMPOUNDS
CRYSTAL STRUCTURE
CRYSTALS
ENERGY
FABRICATION
HEAT TREATMENTS
MATERIALS
MATERIALS WORKING
MECHANICAL PROPERTIES
MICROSCOPY
MONOCRYSTALS
NITRIDES
NITROGEN COMPOUNDS
PNICTIDES
PRESSING
SILICON COMPOUNDS
TEMPERATURE RANGE
360603* - Materials- Properties
360602 - Other Materials- Structure & Phase Studies