Deformation mechanisms of transition-metal disilicides with the hexagonal C40 structure

The deformation mechanisms of (0001)<1210> basal slip in single crystals of five different transition-metal disilicides with the hexagonal C40 structure has been investigated in the temperature range from room temperature to 1500 °C in compression. High resolution transmission electron microscopy of the core structure of 1/3<1210> dislocations is used to deduce the difference in deformation mechanisms. These five different disilicides are found to be classified into two groups depending on deformation mechanism, which is reflected in the difference in the onset temperature for plastic flow. The low-temperature group, which consists of VSi2, NbSi2 and TaSi2, exhibits the onset temperature for plastic flow around 0.3 T/Tm (Tm: melting temperature) and they deform by a conventional shear mechanism. On the other hand, the high temperature group, which consists of CrSi2 and Mo(Si,Al)2, exhibits the onset temperature around 0.6 T/Tm and they deform by a synchroshear mechanism. Factors affecting the deformation mechanism in these C40 disilicides are discussed in terms of directionality of atomic bonding and the relative stability of the C40 phase with respect to the C11b phase.