Stacking fault model of [epsilon]-martensite and its DIFFaX implementation

Plastic deformation of highly alloyed austenitic transformation-induced plasticity (TRIP) steels with low stacking fault energy leads typically to the formation of [epsilon]-martensite within the original austenite. The [epsilon]-martensite is often described as a phase having a hexagonal close-packed crystal structure. In this contribution, an alternative structure model is presented that describes [epsilon]-martensite embedded in the austenitic matrix via clustering of stacking faults in austenite. The applicability of the model was tested on experimental X-ray diffraction data measured on a CrMnNi TRIP steel after 15% compression. The model of clustered stacking faults was implemented in the DIFFaX routine; the faulted austenite and [epsilon]-martensite were represented by different stacking fault arrangements. The probabilities of the respective stacking fault arrangements were obtained from fitting the simulated X-ray diffraction patterns to the experimental data. The reliability of the model was proven by scanning and transmission electron microscopy. For visualization of the clusters of stacking faults, the scanning electron microscopy employed electron channelling contrast imaging and electron backscatter diffraction.