Solidification paths and carbide morphologies in melt-processed MoSi{sub 2}-SiC in situ composites
- Univ. of California, Santa Barbara, CA (United States)
The present investigation was undertaken to elucidate the microstructural evolution of MoSi{sub 2}-SiC in situ composites produced by melt processing. An assessment of the existing liquidus projection was performed by a combination of thermodynamic modeling, analysis of solidification microstructures, and measurements of the thermal history during solidification. Results show that the quasibinary MoSi{sub 2}-SiC eutectic occurs at {approximately}2 at. pct C and 2,283 K, rather than 8 at. pct C and 2,173 K, as previously reported. The ensuing L + MoSi{sub 2} + SiC monovariant line runs almost parallel to the Si-MoSi{sub 2} binary and terminates at a ternary L {leftrightarrow} Si + MoSi{sub 2} + SiC eutectic calculated at 1.5 Mo-0.84 C (at. pct) and {approximately} 1,670 K. The maximum amount of SiC that may be produced by solidification along the quasibinary isopleth is {approximately}37 vol pct, of which {approximately} 35 vol pct grows as primary. Analysis of solidification microstructures shows SiC grows with the cubic {beta} polytype structure (B3), while MoSi{sub 2} grows with the tetragonal C11{sub b} structure. Primary SiC may grow as equiaxed particles, platelets, and hopper crystals. Coupled growth with MoSi{sub 2} leads to SiC in the shape of thin ribbons, sheets, and needles. The facets of the SiC crystal were identified to be of the {l_brace}111{r_brace} and {l_brace}002{r_brace} type, in agreement with the periodic bond chain analysis. The predominant platelike morphology was shown to develop due to a re-entrant twin mechanisms similar to that observed in Si and Ge.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 544063
- Journal Information:
- Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science, Journal Name: Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science Journal Issue: 9 Vol. 28; ISSN 1073-5623; ISSN MMTAEB
- Country of Publication:
- United States
- Language:
- English
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