Microstructural and mechanisms of cyclic deformation of aluminum single crystals

Graduation date: 1996Aluminum single crystals were cyclically deformed in single-slip at small strain amplitudes\ud at 77 K to presaturation. The observed mechanical behavior is consistent with other\ud recent work. The dislocation substructure was analyzed in detail. The structure can be\ud described as consisting of dense bundles or veins of dislocation dipoles, separated by\ud lower dislocation density regions where debris is evident. This debris was determined to\ud be principally relatively short dipole segments. Screw dislocations with the same Burgers\ud vector span the channels. Dislocations were essentially all of the same Burgers vector.\ud In-situ cyclic deformation experiments were successfully performed by the X-Y technique\ud where thin foils are stressed in alternating perpendicular directions. Screw dislocations\ud span the channel and easily move and reverse direction with shear reversal. Our\ud experiments indicate that loops frequently expand from the dipole bundles into the\ud channels and the edge component is absorbed by nearby bundles leaving screw segments\ud behind. Dipole "flipping" was not observed and these edges are relatively difficult to\ud mobilize. There is no obvious evidence for internal backstresses that assist plastic\ud deformation on reversal of the applied shear