Ultrasonic influence on evolution of disordered dislocation structures

Abstract

Evolution of disordered dislocation structures under ultrasonic influence is studied in a model two-dimensional grain within the discrete-dislocation approach. Non-equilibrium grain boundary state is mimicked by a mesodefect located at the corners of the grain, stress field of which is described by that of a wedge junction disclination quadrupole. Significant rearrangement related to gliding of lattice dislocations towards the grain boundaries is found, which results in a noticeable reduction of internal stress fields and cancel of disclination quadrupole. The process of dislocation structure evolution passes through two stages: rapid and slow. The main dislocation rearrangement occurs during the first stage. Reduction of internal stress fields is associated with the number of dislocations entered into the grain boundaries. The change of misorientation angle due to lattice dislocations absorbed by the grain boundaries is evaluated. Amplitude of ultrasonic treatment significantly influences the relaxation of dislocation structure. Preliminary elastic relaxation of dislocation structure does not affect substantially the results of the following ultrasonic treatment. Substantial grain size dependence of relaxation of disordered dislocation systems is found. Simulation results are consistent with experimental data.

Microstructural Evolutions under Ultrasonic Treatment in 304 and 316 Austenitic Stainless Steels: Impact of Stacking Fault Energy

“…The increase in the average misorientation after UST can be ascribed to the destruction of metastable LAGBs and the contribution by ultrasonic waves to the annihilation and absorption of the generated dislocations to the more stable boundaries. Dislocation emission from LAGBs and its incorporation to the grain boundaries under the effect of ultrasonic vibrations, which has been reported by numerical simulations, [31,49,50] is in good agreement with the results of the current analysis. This process needs a high dislocation activity in the structure.…”

“…The effect of grain size on the number of dislocations absorbed by grain boundaries has been probed through numerical simulation. [49,50] It has been shown that the decrease in grain size leads to a lowering of the number of absorbed dislocations. The current experimental results similarly show that dislocation absorption to the grain boundaries is less significant in fine grains, as specified by the dashed ovals in Figure 7b,d.…”

A method for the construction of initial structures for molecular dynamics simulations of nanocrystals with nonequilibrium grain boundaries containing extrinsic dislocations

“…A significant part of the GB mesodefect caused by EGBDs is represented by triple junction disclinations, which arise due to a mismatch of GB misorientation changes induced by normal components of the EGBDs [11,14]. A qualitatively similar field of shear stresses is typical for a quadrupole of disclinations (see, for example, [28]).…”

The Characterization of Fatigue Damage of 316L Stainless Steel Parts Formed by Selective Laser Melting with Harmonic Generation Technique

“…Classical nonlinear acoustics theory shows that second harmonics are mainly induced by the harmonicity of the crystal lattice of materials. The theoretical research of Hikata et al [35][36][37][38] showed that the amplitude of the second harmonics caused by dislocation is directly proportional to the fourth power of dislocation density. Therefore, in the first stage of fatigue loading, the normalized ultrasonic Materials 2022, 15, 718 9 of 13 nonlinear coefficients tended to increase slowly, because the planar dislocation density in the microstructure of the test specimen increased with the increase in fatigue cycles.…”