Deformation twinning at low temperatures in a Hf–V–Nb cubic laves phase

Deformation twinning in the C15 cubic laves phase of the Hf–V–Nb alloy system is analyzed at temperatures between 77 K and room temperature by conventional and high-resolution TEM. In order to reduce the stacking fault energy (SFE), alloy compositions are chosen such that the cubic laves phase composition is close to a region of C14 phase stability. A high density of stacking defects of intrinsic character in the as-homogenized alloy confirms that the SFE has been reduced. Twinning is observed at all temperatures placing a low upper limit on any thermally activated deformation process. Twin clusters are observed which are narrow and have a similar distribution to the stacking defects in the undeformed alloy. The structure of twins and stacking defects is solved via HREM combined with image calculations. Finally, the mechanism of twinning is discussed and the use of alloying to control the SFE or to refine the microstructure in order to increase the low temperature ductility in these intermetallic compounds with complex cubic crystal structures is proposed.