Cyclic plasticity of soft oriented NiAl single crystals at 600 K

Abstract

Cylindrical specimens of stoichiometric NiAl single crystals with axial orientations near [ 2 ¯ 2 3 ] in the stereographic unit triangle were cyclically loaded at 600 K, imposing low plastic strain amplitudes. A main aim was to study the slip phenomena, involving type and persistence of strain localisation, as well as the dislocation patterns occurring after cycling at ɛ pa = 2.5 × 10 −4. Single slip is dominant in the [0 0 1]( 1 ¯ 1 0 ) system on a macroscopic level. Broad cumulative slip bands appear after a sufficiently large number of cycles. Within these bands the strain is considerably concentrated in individual zones of localised slip, although the average strain carried by all of these slip zones is rather small. During a quarter cycle, the slip is highly localised in a small number of thin slip bands. Atomic force microscope (AFM) measurements show that there exists a broad spectrum of local strain amplitudes (LSAs) reaching up to 100%. The mean strain of the LSAs is more than a factor of 150 larger than the average strain of the cumulative zones of localised slip. The cumulative slip bands are not cyclically persistent. The dislocation patterns in a zone of localised slip (ZLS) characteristically differ from those formed in the surrounding matrix. Multiple slip has to be taken into account on a micrometer-scale in order to understand the ZLS dislocation substructure.