The Thermodynamics of Thermally‐Activated Dislocation Glide

Abstract

A general thermodynamic treatment of thermafly-activated glide is given and the following features discueeed: the meaning of force-distance c w e a for dislocation-obshle interaction, the effect of temperature-variations of internal stress on the activation enthalpy, temperature-dependence of flow stress at constant strain-rate and its relation with the stress-dependence of activation volume; differences in behaviour between rigid obstacles (precipitate particles, "Seeger zones") and deformable obshlee (forest dislocations). Application of the theory to "foreat" hardening, precipitation hardening and irradiation hardening outlined.Thermisch aktiviertee Gleiten wird in allgemeiner Form thermodpmiaoh behandelt, und dabei werden folgende Gr6Ben diskutiert : Die Bedeutung der Kraft-Abetands-Kurven fiir Wechselwirkungen zwischen Versetzungen und Hinderniseen, der EinfluB der Temperaturabhiingigkeit der inneren Spannungen auf die Aktivieruugsenthalpie und ihr Zuaammenhang mit der Spannmgnabhiingigkeit dee Aktivierungsvolumene, die Unterschietle im Verhslten von stamen Hindernissen (abgeechiedene Teilchen, , ,Seeger-Zonen") und verformbaren Hindernissen (Waldversetzungen). Die Anwendungen der Theorie auf die ,,Wald"-Hiirtung, Abscheidungs-HMung und Strahlungs-Hisrtnng werden skizziert.

On the Application of Transition State Theory to Atomic-Scale Wear

“…This behavior was explained using the formalism of transition state theory. Articles by Gibbs [34], Hirth and Nix [35], and others describe a detailed model whereby the macroscopic behavior was characterized as the aggregate of a very large number dislocations, each of which has its motion pinned at various points by obstacles (such as crystal defects). In the initial state, the local dislocation segments are in mechanical equilibrium due to the opposing forces of the external applied stress and the local resistance to motion, which is increased by the obstacle, as shown in Fig.…”

“…Therefore, using thermodynamics and rearranging Eq. 3, the rigorous definitions of activation volume DV act and activation enthalpy can be determined as follows [34,37]:…”

An evaluation of rate-controlling obstacles for low-temperature deformation of zirconium

“…If the results would fit a single curve, then that would be a strong indication for only a single rate-controlling mechanism. The total activation enthalpy can be written [24,25] as:…”

Relationships of fracture toughness and dislocation mobility in intermetallics

“…From the theory of thermally activated dislocation motion, the plastic strain rate for material being deformed at the crack tip is [30] [15] [16] where ⌬F is the energy of the intrinsic barrier to dislocation motion, which for most metals is taken to be the P-N barrier energy; is the applied shear stress; v* is the activation volume; k is Boltzmann's constant; and T is absolute temperature. The pre-exponential factor is [30] [17] where N ϭ number of points per unit volume where activation is occurring, A* ϭ area swept out by the activated dislocation, b ϭ Burgers vector, and vЈ ϭ the attempt frequency for dislocation activation, which is proportional to the Debye frequency.…”