Silicides

The formation of silicides is reviewed with the focus on the disilicides, 5–3 silicides and monosilicides, as the three principal useful groups. For the refractory metal-based disilicides, the relationship between the crystal structures C11_b, C40, C49, and C54 is examined in terms of stacking sequences and contrasted in relation to the structures of aluminides. The role of interstitial elements and the in situ composite approaches are emphasized for the complex 5–3 silicides and the monosilicides as being the most adjacent phases to refractory metal-solid solutions. For most silicides with a noncubic crystal structure, the effect of associated anisotropy of the coefficient of thermal expansion (CTE) on the mechanical integrity through processing and application of the material is brought forth as a potentially critical issue. Molybdenum disilicide has received much attention for use as a high-temperature structural material. Recent efforts to produce MoSi₂-base composites are reviewed.