Dj. Tilly et al., INTERFACES IN MOSI2-SIC IN-SITU COMPOSITES SYNTHESIZED BY MELT PROCESSING, Metallurgical and materials transactions. A, Physical metallurgy andmaterials science, 28(9), 1997, pp. 1901-1911
Interfaces between the primary beta-SiC and the surrounding MoSi2 matr
ix in melt-synthesized in situ composites have been investigated, with
emphasis on the chemistry and crystallographic relationships develope
d during solidification. Primary SiC growth occurs with {002} and {111
} facets, both of which are found to template the subsequent nucleatio
n and epitaxial growth of the MoSi2 matrix. Eight independent orientat
ion relationships (ORs) were identified, involving the following combi
nations of planes: {002}(SiC) parallel to (001)(MoSi2) (3 rotational v
ariants), or {101}(MoSi2) {111}Sic parallel to (001)(MoSi2), or {100)(
MoSi2) (2 rotational variants), or {110)(MoSi2) The interfacial relati
onships were rationalized using coincident site lattice arguments as w
ell as energetic simulations based on the Grey-Bohr algorithm. The lat
ter analysis suggests that the:multiplicity of relationships arises fr
om local effects associated with the size and shape of the adsorbate l
ayers preceding the formation of the MoSi2 nuclei. An amorphous carbon
layer, 2- to 5-nm thick, was detected at all interfaces and some of t
he matrix grain boundaries. This interphase is believed to evolve by s
olid-state precipitation of C during postsolidification cooling and is
, in principle, metastable. The C interphase enables easy debonding an
d thus may have important implications for the mechanical performance
of materials involving SiC/MoSi2 constituents.