PSI - Issue 43

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Václav Paidar / Procedia Structural Integrity 43 (2023) 3–8 Author name / Structural Integrity Procedia 00 (2022) 000 – 000

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Table 4. Burgers vectors for partials b3R and b2L (Fig. 3 and 4) metal Ti Mg Zn b3Ru screw 2.57 2.85 2.65 b3Rd screw 2.96 3.27 2.97 b3R edge 0.71 0.77 0.65 b2Lu screw 3.30 3.82 3.04 b2Ld screw 2.24 2.30 2.58 b2L edge 0.62 0.62 0.63

The dislocation widths on both pyramidal planes are summarized in Tables 5 and 6.

Table 5. Widths of dislocations in nm on Pyr.II. metal Ti Mg Zn c/a 1.586 1.623 1.861 width 1.73 1.56 4.42

Table 6. Widths of dislocations in nm on Pyr.I. metal Ti Mg Zn

width 2L width 3R width 3L

3.67 0.78 0.02

1.41 1.15 0.18

1.43 2.89 1.05

Finally, the energies of dissociated dislocations are compared in Table 7. Due to large edge components of the partials b3Lu and b3Ld in the dissociation with Sf3 on Pyr. I (E I 3L), the dislocation energies are higher and the dislocation widths are smaller. The interaction forces between the edge components with the opposite signs are attractive contrary to the repulsive forces between the screw components having the identical direction. For all three elements the energies on the Pyr. II (E II) with the dissociations only into screw partials (Fig. 2) are smaller than for the dissociations on the plane Pyr. I (E I 2L, E I 3R, E I 3L). When we assume that the wider dislocations are more mobile, it can be concluded that in Ti the c+a dislocations prefer to glide on Pyr. I contrary to Zn where the c+a dislocations prefer to glide on Pyr. II. This finding is in agreement with experiments. The cross-slip between two pyramidal planes is more likely in Ti and is almost excluded in Zn. For Mg the tendency to glide on both pyramidal planes is more or less similar.

Table 7. Energies of dissociated dislocations in J/nm metal Ti Mg Zn E II 7.53 3.50 7.14 E I 2L 8.27 3.86 7.59 E I 3R 8.23 3.78 7.59 E I 3L 13.80 6.05 11.17

4. Discusion The mechanisms of plastic deformation in hexagonal metals are discussed, for example, in (Britton, Dunne et al. 2015). In our paper only the role of c+a dislocations in three representative metals (Ti, Mg, Zn) is investigated and the other attributes of materials plasticity, in particular twining, are not considered. A large attention is paid in literature to magnesium that is applied as a light metal in many fields (Wu, Ahmad et al. 2018). Previously, zinc appeared in more papers than in recent years (Rosenbaum 1961). It was confirmed that at room temperature slip occurs in zinc on pyramidal plane II in agreement with our finding. Due to applications in industry and medicine, titanium is still intensely studied (Veiga, Davim et al. 2012). In this paper, a comparison of the metals with different c/a rations (see Table 5) and different melting temperatures (Ti 1948 K, Mg 923 K, Zn 693 K) is presented.