Processing of transition metal silicides for high-temperature applications

Book · Sun Dec 31 04:00:00 EST 1995

OSTI ID:233987

Deevi, S C; Sikka, V K ^[1]

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1. Oak Ridge National Lab., TN (United States)

The authors review and discuss recent developments in the processing and mechanical properties of MoSi{sub 2} and its composites. High-temperature creep rates of MoSi{sub 2} and its composites are compared to those of several intermetallics and discussed in relation to grain-size effects. Thermophysical properties of MoSi{sub 2} and Si{sub 3}N{sub 4} are compared, and the need for functionally graded composites of MoSi{sub 2}-Si{sub 3}N{sub 4} is discussed. This is followed by a discussion of combustion synthesis, reaction synthesis and densification, in-situ composite development, and reactive hot extrusion of metal-silicon mixtures. In combustion synthesis, a heterogeneous reaction occurs between liquid Si and Mo powder to form MoSi{sub 2}. This technique can be applied to obtain composites and alloys of MoSi{sub 2} and various other transition-metal silicides. In-situ synthesis of a composite of MoSi{sub 2}-Al{sub 2}O{sub 3} was carried out by reacting a thermite mixture consisting of MoO{sub 3}, Al, and Si powders. X-ray characterization of the products obtained at various temperatures reveals that the mechanism consists of a reduction of MoO{sub 3} by Al to MoO{sub 2}, followed by a simultaneous oxidation of Al to Al{sub 2}O{sub 3} and a synthesis reaction between reduced Mo and Si to form MoSi{sub 2}. The rate-determining step is found to be reduction of MoO{sub 2} by Al and oxidation of Al to Al{sub 2}O{sub 3}. The thermite reaction was moderated by adding Mo and Si to the mixture of MoO{sub 3}, Al, and Si, such that the ratio of MoSi{sub 2} to the thermite was in the range of 60:40 to 90:10. Reactive extrusion of metal-silicon mixtures of 3Ni-Si and Co-2Si results in a dense product with at least two phases.

• DOE Contract Number: AC05-84OR21400
• OSTI ID: 233987
• Report Number(s): CONF-950908--; ISBN 0-87170-539-7
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM OXIDES
CARBON
CHEMICAL REACTIONS
COMPOSITE MATERIALS
CREEP
EXPERIMENTAL DATA
FABRICATION
GRAIN SIZE
HARDNESS
HOT PRESSING
IN-SITU PROCESSING
INTERMETALLIC COMPOUNDS
MECHANICAL PROPERTIES
MICROSTRUCTURE
MOLYBDENUM SILICIDES
OPTICAL MICROSCOPY
OXIDATION
SILICON CARBIDES
SILICON NITRIDES
SINTERING
SYNTHESIS
ULTIMATE STRENGTH
X-RAY DIFFRACTION
YIELD STRENGTH