Multiscale modeling of plastic deformation of molybdenum and tungsten. III. Effects of temperature and plastic strain rate

Abstract

In this paper we develop a link between the atomic-level modeling of the glide of 1/2〈111〉 screw dislocations at 0 K and the thermally activated motion of these dislocations via nucleation of pairs of kinks. For this purpose, we introduce the concept of a hypothetical Peierls barrier, which reproduces all the aspects of the dislocation glide at 0 K resulting from the complex response to non-glide stresses and expressed in a compact form by the yield criteria advanced in Part II. To achieve this the barrier is dependent not only on the crystal symmetry and interatomic bonding but also on the applied stress tensor. Standard models are then employed to evaluate the activation enthalpy of kink-pairs formation, which is now also a function of the full applied stress tensor. The transition states theory links then this mechanism with the temperature and strain rate dependence of the yield stress.

Microstructure and mechanical properties at different length scales and strain rates of nanocrystalline tantalum produced by high-pressure torsion

“…Therefore, core contraction is needed for a screw dislocation to move in a bcc metal, and this requires a large shear stress. What is more, the yielding of bcc single-crystal metals does not obey Schmid's law, again because of the core structure of screw dislocations, which entails a strong dependence on the stress state [78][79][80]. As a consequence, the Peierls-Nabarro stress for screw dislocations in bcc metals is usually high, and the mobility of the screws is much smaller than that of edge dislocations [81].…”

Analysis of Deformation Kinetics in Seven Body-Centered-Cubic Pure Metals Using a Two-Obstacle Model

“…[45] In light of the uncertainty in actual carbon concentration, the fact that other impurity elements likely contribute tor i ; and inherent scatter in estimation of the fitting parameters, the increase in obstacle strength with carbon concentration observed in Figure 13 supports the dual-obstacle methodology. [43] and in Nb with comparison with a kink mechanism model. [5] The Stein et al data [7] are unique in that the measurements are on single-crystal specimens and the investigators employed special purification techniques to achieve extremely low carbon contents.…”

“…In a comprehensive series of recent articles, [42,43] Gro¨ger and Vitek report on atomistic studies of glide of screw dislocations in Mo and W. The activation enthalpy for formation of kink pairs is determined as a function of stress, and an estimate of temperature dependence of the yield stress follows from the application of transition state theory. The calculated dependence of the activation **As will be shown in Figure 9, the activation volumes between the seven bcc metals analyzed here vary by approximately a factor of 4, which puts into perspective this 35 pct variation in Nb.…”

Peierls barriers of a-type edge and screw dislocations moving on basal and prismatic planes in magnesium

“…The most prominent models developed to date are those by Seeger [13], Dorn and Rajnak [14], Celli et al [15], Koizumi et al [16] and Suzuki et al [17]. The adjustable parameters in these models have to be determined by higher-level calculations, typically by a number of molecular statics simulations of isolated dislocations under stress [18]. One such example is the model of thermally activated cross-slip in Mg alloys developed by Yasi et al [19,20].…”