Strength and deformation mechanism of C40-based single crystal and polycrystalline silicides

Plastic behavior and anomalous strengthening in various C40-type silicide single crystals are reviewed. The anomalous strengthening occurs in binary and ternary C40-type silicides at high temperatures. MoSi2 and WSi2 crystallize in the C11b structure. Additional Mo and W atoms in NbSi2-based silicides may preferentially gather at the superlattice intrinsic stacking fault between two 1/6〈12̄10〉 superpartials and form a strong dragging atmosphere. The anomalous strengthening is due to the dragging atmosphere around moving 1/3〈12̄10〉 superlattice dislocations. Formation of the atmosphere can improve high temperature strength of NbSi2-based silicides with the C40 structure: the anomalous peak temperature is shifted from 1400 to 1600°C, and the peak stress height rises with increasing concentration of Mo and W addition. Attempts to improve the ductility and high-temperature strength of C40-based polycrystalline silicides are also made by controlling the microstructure and species of constituent phase and volume fraction of each phase. Lamellar structure in pseudo binary MoSi2/NbSi2 is produced during the phase transformation from the C40 to C11b phase after the peritectic reaction. The lamellar structure effectively maintains the good thermal stability and improve the high-temperature strength.