Plastic deformation of magnetically isotropic Cr single crystals compressed at 77 K

Ab initio modeling of slip activity in body-centered cubic chromium

“…One can only expect that a lower proportion of 100 dislocations would be obtained than with a single extinction condition, but that the relative density will still be relevant, like in Fe. These 100 dislocations are actually observed as junctions between intersecting 1/2 111 dislocations [5]. At low temperature, 77 K in the work of Holzer et al [5], all 100 and 1/2 111 dislocations are lying along their screw orientation.…”

“…experimental data Observations of dislocations with a 100 Burgers vector have been reported in various experimental studies: in polycrystalline samples at room temperature by Hale and Henderson Brown [4] using a twobeam extinction criterion in transmission electron microscopy, by Reid and Gilbert [3] through a crossslip event incompatible with a 1/2 111 dislocation, and by both McLaren [2] and Garrod and Wain [31] in an annealed sample as part of hexagonal dislocation networks formed by intersecting 1/2 111 dislocations. Holzer et al [5] also report the presence of 100 dislocations in a compressed single-crystal at 77 K oriented at the center of the stereographic triangle, formed by the intersection of two 1/2 111 screw dislocations.…”

“…100 dislocations in bcc metals are the junction product resulting from the interaction of two 1/2 111 dislocations, a reaction driven by elasticity [10]. Such a junction has been observed recently by transmission electron microscopy in Cr by Holzer et al [5] on compressed single crystals at a temperature of 77 K. However, these authors did not report any activity of the 100 {110} slip system for the different orientations of the compression axis they investigated. On the other hand, ab initio calculations have shown that these 100 screw dislocations have a Peierls energy barrier and a Peierls stress which are comparable to 1/2 111 screw dislocations [7].…”

“…11) where slip systems having all three 100 Burgers vectors have the same Schmid factor. For instance, in the case of the [5 9 11] single crystal tested in compression by Holzer et al [5], strong 100 {110} slip activity is expected. The predicted yield stress for the slip systems having the 6 highest Schmid factors are presented in Tab.…”

“…Among all body-centered cubic (bcc) metals, chromium (Cr) is the only one with an antiferromagnetic (AF) order below its Néel temperature of 311 K [1]. At low temperature, as in other bcc metals, screw dislocations control the plastic deformation due to their high lattice friction [2][3][4][5]. These dislocations glide in the {110} planes [2,3,6] and have a Burgers vector equal to the smallest periodicity vectors of the bcc crystal lattice, 1/2 111 .…”