Slip Geometry and Plastic Anisotropy of Body-Centered Cubic Metals

Abstract

The plastic anisotropy of bcc metals comprises the absence of well-defined slip planes, an orientation dependence of the uniaxial flow stress which seems to be in disagreement with Schmid's law of resolved shear stress, and an asymmetry between tension and compression. Recent theoretical and experimental work has shown that these phenomena are closely correlated to elementary slip on {211} planes in an intermediate temperature range. After a discussion of crystallographic peculiarities of h111i {211} slip, a kinematic model for microscopic cross-slip on triplets of slip planes is proposed which, in combination with the well-established model of thermally activated kink-pair formation, allows quantitative calculations of the plastic anisotropy.

Unraveling the temperature dependence of the yield strength in single-crystal tungsten using atomistically-informed crystal plasticity calculations

“…For their part, non-Schmid effects were detected in tests done in the 1930's by Taylor in the wake of his seminal works on plastic flow and strain hardening (Taylor, 1928(Taylor, , 1934a. Subsequent observations and measurements (Šesták & Zárubová, 1965;Sherwood et al, 1967;Zwiesele & Diehl, 1979;Christian, 1983;Pichl, 2002;Escaig, 1968Escaig, , 1974, and a rigorous theoretical formulation of the problem (Duesbery & Vitek, 1998;Ito & Vitek, 2001;Woodward & Rao, 2001;Gröger & Vitek, 2005;Chaussidon et al, 2006;Gröger et al, 2008a,b;Soare, 2014) have established non-Schmid behavior as a principal tenet of bcc plasticity that must be accounted for in order to understand bcc plastic flow. In terms of phenomenology, the two essential aspects to bear in mind are (i) that the resolved shear stress is not independent of the sign of the stress in glide planes of the x111y zone (the so-called twinning/anti-twinning asymmetry), and (ii) that non-glide components of the stress tensor -i.e.…”

Force-matched embedded-atom method potential for niobium

“…[64][65][66][67][68][69][70][71] The cores of ͑1 / 2͒͗111͘ screw dislocations in bcc metals spread into several planes of the ͗111͘ zone. However, no dissociation of dislocations into well-defined partial dislocations has been observed, and no metastable stacking faults that could participate in such dissociation have been identified.…”

“…The results clearly demonstrate the dependence of the CRSS on the sense of shearing and illustrates the wellknown breakdown of the Schmid law in bcc metals. [64][65][66][67][68][69][70][71] This law assumes that components of the stress tensor other than shear in the slip plane in the slip direction play no role in the deformation process and that the critical stress is independent of the sense of shearing. When ͑112͒ is the slip plane, the Schmid-law dependence of the CRSS on has the form 1 / cos͑ + 30°͒, drawn as a dashed curve in Fig.…”

Ab initiobased empirical potential used to study the mechanical properties of molybdenum

“…The motion of dislocations is generally accepted to be responsible for the complex deformation behavior of this transition metal. [1][2][3][4][5][6][7][8] In recent years progress has been made on the description of the properties of screw dislocations using density-functional theory (DFT), tight-binding calculations, and empirical potentials. [9][10][11][12][13][14][15][16][17][18][19] However, DFT and tight-binding techniques are limited to small system sizes which is problematic due to the long-range strain field of dislocations, and current empirical potentials lack the required accuracy for the description of the dislocation structure.…”