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High angular resolution electron backscatter diffraction (HR-EBSD) wascoupled with focused ion beam (FIB) slicing to characterize the shape of theplastic zone in terms of geometrically necessary dislocations (GNDs) in Wsingle crystal in 3 dimensions. Cantilevers of similar size with a notch werefabricated by FIB and were deformed inside a scanning electron microscope atdifferent temperatures (21$^{\circ}$C, 100$^{\circ}$C and 200$^{\circ}$C) justabove the micro-scale brittle-to-ductile transition (BDT). J-integral testingwas performed to analyse crack growth and determine the fracture toughness. Atall three temperatures the plastic zone was found to be larger close to thefree surface than inside the specimen, similar to macro-scale tension tests.However, at higher temperature, the 3D shape of the plastic zone changes frombeing localized in front of the crack tip to a butterfly-like distribution,shielding more efficiently the crack tip and inhibiting crack propagation. Acomparison was made between two identically deformed samples, which wereFIB-sliced from two different directions, to evaluate the reliability of theGND density estimation by HR-EBSD. The analysis of the distribution of the Nyetensor components was used to differentiate between the types of GNDs nucleatedin the sample. The role of different types of dislocations in the plastic zoneis discussed and we confirm earlier findings that the micro-scale BDT of W ismainly controlled by the nucleation of screw dislocations in front of the cracktip.

3D HR-EBSD characterization of the plastic zone around crack tips in tungsten single crystals at the micron scale