Heterogeneous dislocation loop nucleation and free surface effects on plastic deformation: an in situ transmission electron microscopy study

A common feature of dislocation patterns in b.c.c. metals is the large amount of "debris" in the form of many elongated or circular loops. The origin of this debris is recognized as the non-conservative motion of jogs on screw dislocations. Evidence of heterogeneous dislocation loop nucleation prior to creation of the lattice dislocation network is presented. Investigations of the later stages of deformation revealed dynamic behavior of intermediate and large jog creation of loops. It was also found that reaction of a lattice dislocation with a loop can drag the loop to the free surface. All observed phenomena imply higher dislocation activity near the surface, which plays an important role in cyclic deformation.