X-ray topographic studies of dislocations in iron-silicon alloy single crystals

Thin plates cut from melt-grown single crystals of iron + 3.5% silicon were examined by an X-ray transmission topographic method and the spatial arrangement of individual dislocations and of dislocation arrays was investigated. The directions (including the sense in some cases) of dislocation Burgers vectors were identified. It was confirmed that Burgers vectors lie along $\langle$ 111$\rangle$. Reactions such as $\frac{1}{2}[\overline{1}$11] + $\frac{1}{2}$[11$\overline{1}$] = [010] were not observed among the individually resolved dislocations. The minimum separation of dislocations for easy individual resolution was 3 $\mu$m with CoK$\alpha$ radiation and 5 $\mu m$ with AgK$\alpha$. It was demonstrated that a one-to-one correspondence exists between dislocation outcrops and the etch pits produced by the dislocation-etching technique of Sestak (1959). The experiments showed that transmission X-ray topography when applied to metals of moderately heavy atomic weight can give a clear picture of the dislocation configuration in specimens sufficiently thick to be fully representative of the bulk material.