Elementary plastic mechanisms of bcc materials

PhD thesis started in 2014, Benjamin DOUAT

Context. Studied for over 50 years, the elementary plastic mechanisms of body cubic centered materials are still currently the subject of debate, particularly regarding the involved slip planes of screw dislocations. Microscopic observations of slip traces are often uncertain, which is explained by cross slip from one slip plane to another.  many atomistic simulations were conducted to understand the basic mechanisms, but without experimental comparison at the atomic scale.

Results. Niobium single crystals {111} were deformed at different temperatures. Surface is observed by STM to a first stress level (Fig. 1a), then an increment of the stress generating the emergence or glide of dislocations (Fig. 1b).Slip planes and Burgers vectors of dislocations was identify at atomic scale (Fig. 1c). These observations were comparing with other studies, in particular atomistic simulation, to identify the basic mechanisms of plasticity.

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Figure 1: Slip traces at the atomic scale at the surface of Nb(111) single crystals deformed at T= 200K at 5.5% plastic strain (τ=68 MPa). Two of the three traces exhibit an ending point that characterizes the position of the dislocation going through the bulk just beneath the surface.















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