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

Plastic behavior and anomalous strengthening in various C40-type silicide s ingle crystals are reviewed. The anomalous strengthening occurs in binary a nd ternary C40-type silicides at high temperatures. MoSi2 and WSi2 crystall ize in the C11(b) structure. Additional Mo and W atoms in NbSi2-based silic ides may preferentially gather at the superlattice intrinsic stacking fault between two 1/6[1 (2) over bar 10] superpartials and form a strong draggin g atmosphere. The anomalous strengthening is due to the dragging atmosphere around moving 1/3[1 (2) over bar 10] superlattice dislocations. Formation of the atmosphere can improve high temperature strength of NbSi2-based sili cides with the C40 structure: the anomalous peak temperature is shifted fro m 1400 to 1600 degrees C, and the peak stress height rises with increasing concentration of Mo and W addition. Attempts to improve the ductility and h igh-temperature strength of C40-based polycrystalline silicides are also ma de by controlling the microstructure and species of constituent phase and v olume fraction of each phase. Lamellar structure in pseudo binary MoSi2/NbS i2 is produced during the phase transformation from the C40 to C11(b) phase after the peritectic reaction. The lamellar structure effectively maintain s the good thermal stability and improve the high-temperature strength. (C) 1999 Elsevier Science S.A. All rights reserved.