The loss of coherency of precipitates and the generation of dislocations

Abstract

The theory of Brown, Woolhouse and Valdrè (1968) is extended to include the possibility of the nucleation of interface dislocations by prismatic punching and the condensation of point defects. It is shown that neither process can occur spontaneously (i.e. without the introduction of dislocations by another process such as deformation or irradiation) unless the misfit exceeds a critical value, estimated to be 0·05. Furthermore, unless the radius of the precipitate exceeds certain critical values, the processes will not occur because the energy of the system is not thereby lowered. A comparison of the theory with experiment enables limits to be placed on the stress necessary to cause the generation of dislocations in a perfect lattice, and at an incoherent interface. In the former case the generation stress is higher than hitherto supposed; but in the latter case it appears that an incoherent interface behaves as an ideal source of dislocations, in the sense that when the energy of the system can be lowered by their generation, they will be formed.