Stacking fault aggregation during cooling composing FCC-HCP martensitic transformation revealed by in-situ electron channeling contrast imaging in an Fe-high Mn alloy.

To understand the mechanism of FCC-HCP martensitic transformation, we applied electron channeling contrast imaging under cooling to -51°C and subsequent heating to 150°C. The stacking faults were randomly extended and aggregated during cooling. The stacking fault aggregates were indexed as HCP. Furthermore, the shrink of stacking faults due to reverse motion of Shockley partials was observed during heating, but some SFs remained even after heating to the finishing temperature for reverse transformation (Af: 104°C). This fact implies that the chemical driving force of the FCC/HCP phases does not contribute to the motion of a single SF but works for group motion of stacking faults.