Slip body-centred cubic

Slip in hexagonal metal crystals occurs mainly parallel to the basal plane of the unit cell, normal to the c axis. The slip systems can be described as 000 1 (1 1 20), of which there are three. Body-centred cubic metals have slip described by 1 1 0 (I 1 1), giving 12 combinations in aU. Other slip systems also occur in metals, but those described operate at lowest energies. 

Fig. 6.15. 110 (111) slip systems in body-centred cubic metals Table 6.2. Slip systems in body-centred cubic metals... 

The body-centred cubic crystal is not close-packed. The slip systems with the closest packed directions and planes in this lattice are of the type 110 (111) (figure 6.15). With two slip directions per plane and six different slip planes, twelve slip systems result. As summarised in table 6.2, slip is also possible on other crystallographic planes that are only slightly more difficult to activate [55]. 

If we consider the Peierls force from section 6.2.9 as obstacle, it can also be overcome by thermal activation. This is especially relevant if the Peierls force is large i. e., when slip is along planes that are not close-packed, for example in body-centred cubic lattices. For this reason, the yield strength of body-centred cubic lattices is strongly dependent on the temperature, different from face-centred cubic metals (figure 6.29). The Peierls stress can reach values of up to several hundred megapascal. 

Fig. 6.14. Slip systems in face-centred cubic metals. The slip planes are the body diagonals the slip directions lie on the plane diagonals or on the edges of the octahedron in figure (c), respectively...

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