Dislocation-boundary interactions are studied in TiAl and Al by means of in situ straining experiments in transmission electron microscopes (TEM). The results in TiAl allow us to measure the strength of domain boundaries against the motion of ordinary dislocations and twins. The results in Al are used to analyze the interaction between dislocations and cell walls. Parameters involved in the Hall-Petch law are then deduced from these observations.
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