Anomalous behavior of an $\alpha\to\gamma$ phase transition in iron: results of in situ neutron diffraction experiment

Neutron diffraction studies of a $\alpha\to\gamma$ structural phase transition ($T_c\approx911\,^\circ$C) in iron samples at different initial states have been performed. The anomalous disappearance of a diffraction pattern is observed in iron in the region of the $\alpha\to\gamma$ phase transition. At repeated heating processes of an as cast sample, this effect becomes less pronounced and it is absent at the heating of iron powder. The observed effects have been assumingly attributed to the formation of small paracrystalline clusters with a large dispersion of the cell parameters in the process of phase transition. The kinetics of formation of clusters is slowed in as cast samples, which leads to the temporal disappearance of the diffraction pattern. These results make it possible to reconsider the atomic processes in the $\alpha\to\gamma$ phase transition in iron.