Orientation relationship between the bec and σ phases in Cr-Co alloys

To obtain deeper understanding of the σ structure, the formation of the σ structure in the (bcc→bcc+σ) reaction at 873K and 1173K have been investigated by transmission electron microscopy. As for the orientation relationship between the bcc and σ structures, as a result, both the common first relation of [110]_bcc//[100]_σ and three second relations given by α=0°, 33°, and 64° were found for the 1173K annealing, where α is an angle between the [1l0] _bcc and [001]_σ directions. For the 873K annealing, on the other hand, there was only one second relation with α=0°. Based on the α=0° relation found for both annealing temperatures, the features of atomic shifts in the σ-structure formation from the bcc structure were also discussed.