An in-situ transmission electron microscopy study was conducted at room temperature in order to understand an underlying mechanism on room temperature ductility of TiAl alloys. Also, melecular dynamics simulation was conducted to calculate the stacking fault energy of TiAl alloys and to show which deformation mode is dominant. From in-situ straining transmission electron microscopy experiments, it was revealed that the crack path and deformation mode is different between the TiAl alloys with/without room temperature ductility. The crack in TiAl alloys having room temperature ductility interacted with lamellae by forming bridging ligaments between the two α2 lamellae and the γ lamellae. In contrast, the cracks in TiAl alloys without room temperature ductility propagated along grain (colony) boundaries showing brittle intergranular fracture. From the quantitative in-situ TEM experiements, it was found that the γ lamellar of TiAl alloys having room temperature ductility was deformed by slip (Fig. 1). However, the γ lamellar of TiAl alloys without room temperature ductility was deformed by deformation twin (Fig. 2). The difference in deformation mode was explained by stacking fault energy of the TiAl alloys which was calculated by molecular dynamics. The TiAl alloy with low stacking fault energy was deformed by deformation twin (Fig. 2) whereas the TiAl alloy with high stacking fault energy was deformed by dislocation slip (Fig. 1). Furthermore, the role of lamellar orientation of tensile direction on deformation behavior was examined using Schmid factor of each orientation.

Finally, we proposed the important microstructural factors to have room temperature ductility of TiAl alloys.

Figures:

Fig. 1. Dark field image of alloy having room temperature ductility taken during in-situ TEM experiment. White arrows are indicating dislocations.

Fig. 2. Dark field image of alloy having no room temperature ductility taken during in-situ TEM experiment. White arrows are indicating deformation twins.

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EMC Abstracts - https://emc-proceedings.com/abstract/understanding-the-enhanced-ductility-of-tial-alloys-using-a-hybrid-study-of-in-situ-tem-experiment-and-molecular-dynamics/