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Atomistic simulations of (a/2) < 111 > screw dislocations in bcc Mo using a modified generalized pseudopotential theory potential

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Atomistic simulations using a modified generalized pseudopotential theory potential and Green's function boundary conditions were employed to determine the Peierls stress of rigid straight (a/2)<111> screw dislocations for the application of shear stresses on {110}- and {112}-type planes in bcc Mo. It is found that the Peierls stress of(a/2)<111> screw dislocations for the application of shear stress on the {110}planes is (0.0175-0.020). Large twinning-antitwinning asymmetry is found for the application of pure shear stress on the {112} planes with the Peierls stress along the twinning direction being (0.0125-0.020) and along the antitwinning direction to be (0.050-0.0562). The Peierls stress of screw dislocations for the application of tensile and compressive stresses along {001}, {110}, {111} and {201} directions were also determined. A large tension compression asymmetry is observed for the {001}, {110} and {111} directions. This is a manifestation of the twinning-antitwinning asymmetry observed in the pureshear stress calculations.Atension-compression asymmetryis also observed for the {201} direction, indicating that non-glide stress effects are also important in determining the Peierls stress. To facilitate an understanding of (a/2)<111> screw dislocation motion by the kink pair mechanism, the core structure and energetics of six possible kinks and two antiphase defects on (a/2)<111> screw dislocations werealso determined.Itis foundthatthe kinkpair formation energy at infinite separation distance varies between 1.46 and 2.10eV, which is in reasonable accord with the experimental value of 1.27eV.
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Document Type: Research Article

Publication date: 2001-05-01

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