Microstructure and tensile creep mechanisms of an in situ reinforced silicon nitride
- Allied Signal, Inc., Morristown, NJ (United States). Corporate Research and Technology
The creep behavior of an acicular-grained Si{sub 3}N{sub 4} in the temperature range of 1260--1400 C under 50--350 MPa tensile stress was investigated. The viscous flow of an amorphous grain boundary phase and uninhibited grain boundary sliding resulted in a fast initial creep regime characterized by a stress exponent = 1.8 and an activation energy = 509 kJ mol{sup {minus}1}, which increased to 3.2 and 1,054 kJ mol{sup {minus}1}, respectively, in the secondary creep regime. Between these two regimes the creep rate dropped rapidly due to grain interlocking and loading of the acicular grains parallel to the tensile axis. An enhanced dislocation activity in the parallel grains and cavitation in the grain pockets were observed, but their roles in the creep deformation appear minor. It is proposed that the mechanism controlling the secondary creep regime is the nucleation and growth of surface steps on the atomically smooth (100) grain boundary plane through the solution/precipitation process.
- OSTI ID:
- 445352
- Journal Information:
- Acta Materialia, Vol. 45, Issue 1; Other Information: PBD: Jan 1997
- Country of Publication:
- United States
- Language:
- English
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