Question

Why do dislocations always glide on crystallographic planes? What planes do they glide on in f.c.c. crystals?

(Please type answer or write clearly in print so I can understand)

Answer 1

Solution: The process of movement of dislocations on a certain slip plane along the slip direction is called Dislocation Glide. It is primary mechanism for plastic deformation in crystals. Dislocations usually glide on various slip planes in response to the applied external stresses.Dislocations are always prefer to move on close packed planes. Because these are the planes with widest inter-planar spacing in crystals. When the external stress is applied to it and it forms as shear stress in an appropriate direction on the dislocation for glide to occur. Dislocation glide allows plastic deformation to occur at a much lower stress than would be required to move a whole plane of atoms past another. Dislocation glide mostly occurs on crystallographic planes due to those planes are the closed packed planes. There fore dislocations can move easily.

The slip plane and slip direction for FCC crystals is {111} plane with movement direction along <110>. And {111} plane is the most close packed plane in FCC whereas <110> is the close packed direction. Therefore, dislocations prefer to glide on {111} plane along <110> direction in FCC crystals.