Dj. Tilly et al., SOLIDIFICATION PATHS AND CARBIDE MORPHOLOGIES IN MELT-PROCESSED MOSI2-SIC IN-SITU COMPOSITES, Metallurgical and materials transactions. A, Physical metallurgy andmaterials science, 28(9), 1997, pp. 1889-1900
The present investigation was undertaken to elucidate the micro struct
ural evolution of MoSi2-SiC in situ composites produced by melt proces
sing. 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 solid
ification. Results show that the quasibinary MoSi2-SiC eutectic occurs
at similar to 2 at. pct C and 2283 K, rather than 8 at. pet C and 217
3 K, as previously reported. The ensuing L + MoSi2 + SiC monovariant l
ine runs almost parallel to the SiMoSi2 binary and terminates at a ter
nary L <-> Si + MoSi2 + SiC eutectic calculated at 1.5Mo 0.84C (at. pc
t) and similar to 1670 K. The maximum amount of SiC that may be produc
ed by solidification along the quasibinary isopleth is similar to 37 v
ol pct, of which similar to 35 vol pct grows as primary. Analysis of s
olidification microstructures shows SiC grows with the cubic beta poly
type structure (B3), while MoSi2 grows with the tetragonal C11(b) stru
cture. Primary SiC may grow as equiaxed particles, platelets, and hopp
er crystals. Coupled growth with MoSi2 leads to SiC in the shape Of th
in ribbons, sheets, and needles. The facets of the SiC crystals were i
dentified to be-of the {111} and {002} type, in agreement with the per
iodic bond chain analysis. The predominant platelike morphology was sh
own to develop due to a re-entrant twin mechanism,similar to that obse
rved in Si and Ge.