Transmission Electron Microscopic Observations of Dislocations Resulting from Allotropic Transformation of Pure Iron

Abstract

The phenomena resulting from the allotropic transformation of thin foils as well as thick specimens (7/100 mm thickness) of pure iron were examined by transmission electron microscopy. The cloudy structure in the specimens quenched from a temperature higher than the α→γ transformation point was observed in both cases. The cloudy structure is seen in α phase and consists of lattice defects such as dislocations distributed so densely that they can be unresolved with the present electron microscopy. The lattice defects can be annihilated and displaced by the subsequent annealing at a temperature below the transformation point. At the same time, irregularly arranged dislocations, dislocation networks, sub-boundaries consisting of dislocations can be observed. When a thin foil is cooled slowly from a temperature higher than the transformation point, the cloudy structure and dislocations can not be observed. The thick specimen cooled down slowly has irregularly arranged dislocations and sub-boundaries consisting of dislocations.