A dislocation link length model for strain hardening in stage II of polycrystalline metals of high stacking fault energy

Abstract

A theoretical strain hardening model is developed. The model takes the distribution of dislocation link lengths into account. During plastic deformation this distribution is assumed to change by three different subprocesses. (1) Under the action of a continuously increasing applied stress, dislocation links are released and start gliding. (2) The released links expand into loops by glide and thereby produce strain. New dislocation links are formed when the loops are eventually arrested in the network. (3) Stress-induced annihilation of screw dislocations occurs in the network. To verify the model experiments on polycrystalline nickel were performed. It is shown that the model is able to simulate the experimentally determined stress-strain curve, the increase in the dislocation density and the behaviour of the distribution of dislocation link lengths. The following important results were obtained. (1) The value predicted by the model for the diameter of an expanded dislocation loop is in agreement with the experimentally measured distance between dense dislocation tangles. (2) The model predicts that dynamic recovery processes are very active.