The permanent changes
in shape and dimensions of metals can be carried out by plastic deformation mechanisms.
Crystal structure and lattice parameters remain unaltered during plastic
deformation. Plastic deformation increases the number of imperfections in
metals. The two main processes involved in plastic deformation are slip and
twinning. In slip, atoms move over a number of interatomic distances relative
to their initial positions. The displacement step magnitude is equal to full
interatomic distance. The orientation of displaced region and undeformed region
remains the same. Movement by an atom is a fraction of interatomic distance in
twinning process. The orientation of twinned region and untwined regions are
not same. Slip mechanism is preferred during high temperature and lower strain
rate cases. At lower temperature, high strain rate cases, twinning is employed.
