Electron microscopic studies of the laves phases TiCr₂ and TiCo₂

It is shown that the Laves phases TiCr₂ and TiCo₂ exhibit polytypism. Apart from the structure reported in the literature (MgZn₂) the alloy TiCr₂ also crystallizes in the 4H form. The alloy TiCo₂ exhibits the 6H form and also a 12‐layer sequence, next to the structures described in the literature (cubic and 4H). The transformation from one phase into another one presumably proceeds by a shear mechanism. The cubic phase of TiCo₂ contains a multitude of extrinsic stacking faults. The nature of the faults was determined using the {311} type reflections. In an appendix the method for determining the type of fault in f.c.c. crystals described in reference [4] is extended to {311} reflections.