Elektronenmikroskopische untersuchung der versetzungsanordnung verformter kupfereinkristalle im belasteten zustand

Copper single crystals oriented for single glide were deformed in tension at 78°K and irradiated before load-removal with fast neutrons at 4°K or 20°K. It was shown in two preceding papers (Mughrabi 1971 a, b) that the dislocation arrangements of these crystals which were thus stabilized in the stress-applied state differ in stages I and II from the dislocation arrangements of similarly deformed crystals irradiated in the unloaded state. In this paper the dislocation densities in the stress-applied and stress-removed states, as determined by electron microscopy, are compared. It is found that in both cases in stage II the primary dislocation density ρp increases linearly with flow stress τ whereas the secondary dislocation density ρs increases quadratically with τ and that the dislocation densities are of comparable magnitude in the stress-applied and in the unloaded state. The density of free primary dislocations, however, is about twice as large in the stress-applied state (where a substantial number of primary dislocation groups are observed) as in the unloaded state. It is suggested that the linear increase of ρp with τ may be explained in part by taking into account that deformation occurs not only by the glide of newly generated dislocations but also by the glide of the existing dislocations. The densities of free primary dislocations can be used to estimate the reversible and irreversible contributions to reverse dislocation glide upon unloading and the corresponding clastic modulus defects in the stress-applied and in the unloaded states. The results are in qualitative agreement with other investigations.