Secondary Slip Systems Research Articles

The deformation behavior of isoaxial bicrystals of Fe-3%Si

The slip occurring in bicrystals of a high purity Fe-3 %Si alloy subjected to small plastic strains by deformation in compression was investigated using etch pitting techniques. Four isoaxial types of bicrystals, each containing a planar boundary parallel with the compression axis, were studied. Each of the component crystals was oriented for 〈111〉 {011} type single slip. The deformation behavior is examined in terms of the compatibility requirements imposed at the grain boundary plane and the effect of elastic anisotropy on the mutual interaction between crystals. Elastic incompatibility at the grain boundary plane is found to give rise to local stresses which result in the operation of secondary slip systems not normally expected to be operative in the individual single crystal components.

APPLICATION OF X-RAY TOPOGRAPHY TO THE ANALYSIS OF THE DISLOCATION ARRANGEMENT IN DEFORMED COPPER SINGLE CRYSTALS

The paper deals with the application of Berg–Barrett X-ray topography to deformed copper single crystals. The imaged surfaces were sectioned from the deformed bulk crystals parallel to low-index planes.In stage I of the work-hardening curve, the braids of primary edge-dislocation dipoles, well known from electron transmission microscopy, have been observed over lengths of several tenths of a millimeter. Whereas in stage 1 the slip appears to be rather homogeneous and without strong interaction between primary and secondary slip systems, the transition region to stage 11 displays, as a characteristic feature, a systematic interaction of both types of slip systems, giving rise to layer-like dislocation structures about parallel to the primary slip plane. These layers, as in stage 11, are connected with a special type of lattice rotation. In stage II, dislocation walls or wall fragments perpendicular to the primary slip direction are observed. Generally, these walls are accompanied on either side by an extended region with an excess density of primary edge dislocation of one sign ("kink-walls"). As an example, the excess density at a flow stress τ ≈ 1–2 kg/mm2 is found to be of the order of 108/cm2.

Latent hardening in aluminum

The flow stresses and the initial work-hardening slopes in all 24 slip systems were measured by isoaxial compression tests on plates out out of aluminum single crystals which had previously been deformed in single slip to a standard stress in stage III. The flow stress results fell into two groups: all slip systems with the same slip plane as the primary were, within the scatter, indistinguishable from the primary slip system; all other systems fell, with no further distinction discernible, into a large group with a flow stress raised by 10 to 30%. In the latter group, the initial hardening slope was usually lower than in the primary system. In only one system, corresponding to obtuse cross-slip, was a negative initial hardening slope ever observed. The rate sensitivity of flow stresses and of hardening slopes was measured in 9 secondary systems and was indistinguishable from that of the primary system. The results on flow stresses may be interpreted by postulating that the moving dislocations surround rather than overcome the obstacles in their path, and that the obstacles generated during the previous single slip are arranged in a pattern which distinguishes the slip plane. Furthermore, this arrangement must be polarized, since some initial hardening slopes were found to depend on the sign of the strain. A qualitative connection between the initial work-hardening slopes in secondary slip systems and the orientation dependence of primary work-hardening is established. These conclusions from the experiments are in accord with those from a recently proposed theoretical treatment, the Statistical Theory of Work-Hardening.

Stresses on secondary systems due to piled-up groups of dislocations of arbitrary orientation

Abstract Stress-fields around piled-up groups of dislocations of arbitrary orientation have been calculated by replacing the discrete dislocations by a continuous distribution of infinitesimal dislocations. Previous calculations by Mitchell (1964) have been performed on edge and screw dislocation pile-ups. In the present paper the case of 60° dislocations has been considered in particular, since in face-centred cubic crystals the dislocations will lie parallel to the intersection of the primary and conjugate or critical slip planes. It is shown that the stress-fields on many secondary slip systems are large and are capable of producing secondary slip over distances of the order of the pile-up length. Considerable reduction of long-range stresses is possible by the formation of tangles of primary and secondary dislocations whose Burgers vectors add up to zero and by the formation of small angle tilt boundaries. It is necessary that the primary and secondary dislocation densities should be of the same order...

Secondary slip and internal stresses in single crystals

Abstract The density of secondary dislocations (other than ‘dipoles’) cannot increase by more than an order of magnitude during ‘single slip’. This is shown by a theoretical analysis of the minimum strain that should be caused by a large-scale generation of secondary dislocations, and of the stresses necessary for it; neither of these is in accord with recent macroscopic measurements. It is also shown that even if a sufficiently large number of dislocations were generated on secondary slip systems, internal stresses associated with primary dislocations in f.c.c. materials could not be effectively relieved by secondary slip other than cross-slip and possibly slip on both co-planar systems. Internal stresses of significant magnitude must therefore exist in deformed single crystals and must be mostly due to primary dislocations.

Plastic deformation of single crystal ice

Single crystal ice was deformed in tension at constant strain rates at temperatures between − 42°C and 0°C. For shear stresses below 100 psi and nominal strains less than 25 per cent (starting with asgrown crystals), basal slip was the primary mechanism of deformation. No preferred crystallographic slip direction or work hardening were observed. The rate of basal glide in the direction of maximum shear stress is given by γ ̇ = (2.25 ± 1.5) × 10 7γτ n(γ) exp(−14.3 ± 1.5 × 10 3 RT ) min −1 , where γ is the resolved shear strain, τ is the resolved shear stress (psi) and n equals 2.5 for low strains and decreases with strain, with an average value of about 2.0 for nominal strains less than 25 per cent. Annealing after deformation has no effect on subsequent deformation behavior of ice. Etch pit evidence indicates the existence and activity of secondary slip systems during deformation. It is proposed that the observed plastic deformation of ice results from glide of dislocations whose velocity is limited by a temperature activated process.

Unloading effects in crystals—I the unloading yield point effect

The orientation dependence of the “unloading yield effect” in copper single crystals was investigated. The maximum relative increase in flow stress due to unloading was observed to be orientation independent. An orientation dependence of the variation of the unloading yield with prestrain was observed. The role of secondary slip systems in establishing the unloading yield effect was investigated utilizing combined tensile-torsion deformation. A mechanism for the establishment of the unloading yield effect based on a forest dislocation interaction is proposed.

The Orientation Dependence of Work?Hardening in Crystals of Face-centred Cubic Metals

It is shown that the principal features of the observed orientation dependence of work-hardening can be accounted for in terms of the likelihood of formation. Of Lomer-Cottrell sessile dislocations in two directions in tb" primary slip plane. This is deduced from the known variation of resolved shear stress with orientation, for the possible secondary slip systems, and metallographic observations of slip and deformation bands.

X線回折顕微法によるアルミニウム結晶の束状すべりの解析

By the Berg-Barrett method, X-ray diffraction micrographs of the clustered slip region in elongated aluminium single crystals were taken. The micrographs taken showed four kinds of striations (S1, S2, S′, Sb) related with the active slips. Analysing these striations the following have been found: (1) The striations S′ are observed in both the primary and the secondary slip regions, the former corresponding to the small secondary slip region taking place in the primary slip region, and the latter the other way round. (2) In the secondary slip region there are no kink bands belonging to the secondary slip system but the strain due to deformation is concentrated near the boundary between the primary and the secondary slip regions, probably originated from the constraints due to the lattice deformation in both the regions. (3) The striations S1 are straight and inclined, in the present case, by several degrees of arc to the primary slip trace, in an extent larger than can be attributed to experimental error. (4) The primary slip region, compared with the secondary one, has a larger bending strain of long range (of the order of the width of a kink band).