INSITU STRAINING OF FE-AL IN A TRANSMISSION ELECTRON-MICROSCOPE

In situ straining experiments have been performed in a transmission electron microscope in an attempt to understand the differences in fracture behaviour that occur as a function of composition in Fe-Al. These experiments could not find differences in the dislocation behaviour in thin foils, suggesting that bulk brittle intergranular fracture of stoichiometric FeAl does not involve dislocation motion. In all compositions, dislocation generation was profuse at the foil edges and at grain boundaries. The grain boundaries presented little barrier to slip. Slip was planar, occurring in broad bands and often on multiple systems within an individual grain. Dipoles and loops were left as debris behind gliding dislocations, even though there was no evidence of dislocation interactions, suggesting that the loops formed through a double cross-slip mechanism.