Formation of dislocation patterns under irradiation (original) (raw)
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Point-defect-driven dislocation patterning during deformation under irradiation
Applied Physics A Solids and Surfaces, 1993
Dislocation patterning driven by interactions of dislocations with deformation-induced point defects is considered. The effect of concurrent irradiation-induced production of point defects is also included. The uniform time-dependent solution of the set of equations describing the evolution of the system is "probed" by small periodic perturbations. A linear stability condition obtained in this way as well as the preferred wavelength of the emerging pattern depend on the values of the parameters reflecting biases in the production and annihilation of vacancies and interstitial atoms. It is proposed that by studying the effect of different types of radiation and different irradiation intensities on the occurrence and the wavelength of the dislocation pattern information about the deformationinduced point defect production bias may be obtained.
Spatial instabilities and dislocation-loop ordering in irradiated materials
Physical Review B, 1989
The formation of inhomogeneous distributions of vacancy loops in irradiated materials is discussed in the framework of a dynamical model based on the rate theory of radiation damage. Dislocation structures are associated with dynamical instabilities due to the competition between defect motion and interactions. The dependence of the critical wavelength of the microstructures on material variables, such as the displacement-damage rate, network-dislocation density, or temperature, is obtained. The postbifprcation analysis is performed in the weakly nonlinear regime, where the selection and stability properties of three-dimensional structures are investigated.
Spatial ordering of nano-dislocation loops in ion-irradiated materials
Journal of Nuclear Materials, 2014
Defect microstructures formed in ion-irradiated metals, for example iron or tungsten, often exhibit patterns of spatially ordered nano-scale dislocation loops. We show that such ordered dislocation loop structures may form spontaneously as a result of Brownian motion of loops, biased by the angular-dependent elastic interaction between the loops. Patterns of spatially ordered loops form once the local density of loops produced by ion irradiation exceeds a critical threshold value.
Dislocation - Point Defect Interactions
In book: Mechanical SpectroscopyEdition: Materials Science Forum, vol. 366-368Chapter: 3.3Publisher: Trans Tech Publications, Switzerland, 2001
The dislocation-point defects (DPDs) interactions which can be understood on the basis of the dislocation string model are discussed. These DPS take place when the kink pair formation on the dislocations, associated with the dislocation-lattice interaction, becomes very easy, at temperatures higher than the temperature of the Bordoni peak in fcc metals, and higher than the temperatures of the γ peak for the screw dislocations of the a peak for the edge dislocations in bcc metals.
On the Nucleation of Dislocations at a Crystal Surface
physica status solidi (b), 1993
An exact expression for the elastic energy associated with a semicircular shear dislocation loop emanating from a free surface is derived (within continuum dislocation theory) and compared with an earlier approximation. The energy required to activate a semicircular dislocation loop into its unstable "saddle-point'' configuration is then recalculated , based on the modified expression for the self-energy. It is found that the shear stress necessary to emit the loop, as a function of temperature, is almost 50% less than earlier estimates. The principal drawback to this type of calculation is also discussed, namely, that the critical radius of an incipient dislocation loop is on the order of one atomic spacing, which is too small for a continuum theory to be valid. Ein exakter Ausdruck fur die elastische Energie eines halbkreisformigen Scherversetzungsringes, der von einer freien Oberflache ausgeht, wird im Rahmen der Kontinuumsversetzungstheorie berechnet und mit fruheren Naherungen verglichen. Die Aktivierungsenergie, um einen halbkreisformigen Versetzungsring in die instabile Sattelpunktskonfiguration zu bringen, wird aufgrund des modifizierten Ausdrucks fur die Selbstenergie neu berechnet. Man findet, daB die zur Emittierung eines Ringes notwendige Schubspannung als Funktion der Temperatur etwa 50% niedriger ist als fruher angenommen. Die prinzipielle Schwachstelle dieser Berechnungsweise wird auch diskutiert, nlmlich, daR der kritische Radius eines anfanglichen Versetzungsringes in der GroRenordnung eines Atomabstandes liegt, was zu klein ist fur eine hier noch gultige Kontinuumstheorie.
International Journal of Computer Applications, 2014
Using a personnel computer, we have simulated the diffusion and agglomeration of point defects in thin foil under high energy electron irradiation. The physical model has been developed by using the Monte Carlo technique. Four types of reactions are assumed to take place: di-interstitial creation by agglomeration of two free interstitials, vacancy-interstitial annihilation, interstitial trapping by dislocation loops and interstitial annihilation on the sample surfaces. In the simulation only interstitials are mobile and extended defects are assumed to be interstitial type. We have calculated the concentration of point defects, extended defects and the size of the latter. We compared them to the results of the Chemical Reaction Rate Theory (CRRT). It has been found that the dislocation loops are distributed in the center of material leaving areas denuded close to the surface and the loops radius is also strongly dependent on the location of the defect in thin foil with respect to the results of experimental and CRRT. To explain the origin of these phenomena we have exploited the spatial distribution of vacancies close to free surfaces and around dislocation loops. These types of informations are totally missing in the CRRT and experimental.
Journal of Nuclear Materials, 2002
During irradiation, mobile defects, defect clusters and impurity atoms segregate on dislocations. When an external stress is applied, plastic flow is initiated when dislocations are unlocked from segregated defects. Sustained plasticity is achieved by continuation of dislocation motion, overcoming local forces due to dispersed defects and impurities. The phenomena of flow localization, post-yield hardening or softening and jerky flow are controlled by dislocation-defect interactions. We review here computational methods for investigations of the dynamics of dislocation-defect interactions. The influence of dislocations on the motion of glissile self-interstitial atoms (SIAs) and their clusters is explored by a combination of kinetic Monte Carlo and dislocation dynamics. We show that dislocation decoration by SIAs is a result of their 1-D motion and rotation as they approach dislocation cores. The interaction between dislocations and immobilized SIA clusters indicates that the unlocking mechanism is dictated by shape instabilities. Finally, computer simulations for the interaction between freed dislocations and stacking fault tetrahedra in irradiated Cu, and between dislocations and microvoids in irradiated iron are presented, and the results show good agreement with experimental observations.
Overview on dislocation-point defect interaction: the brownian picture of dislocation motion
Materials Science and Engineering A, 2004
The interactions between dislocations (D) and point defects (PD) are one of the most important causes of mechanical damping in metals. In the past 40 years, many experimental results have been obtained and published, from which it appears that two fundamental behaviors can be observed when dislocations interact with motionless point defects: thermally activated behaviors and athermal behaviors. In this paper, it is shown that these two observed behaviors can be consistently explained by a "brownian picture" of the motion of dislocations interacting with PD distributed at different distances from the dislocation glide plane.
Geometrically necessary dislocation fingerprints of dislocation loop absorption at grain boundaries
Physical Review Materials
We present a numerical methodology to compute the Nye-tensor fingerprints of dislocation loop absorption at grain boundaries (GBs) for comparison with TEM observations of irradiated polycrystals. Our approach links atomistic simulations of self-interstitial atom (SIA) prismatic loops gliding toward and interacting with GBs in body-centered cubic iron with experimentally extracted geometrically necessary dislocation (GND) maps to facilitate the interpretation of damage processes. The Nye-tensor analysis is strongly mesh-size dependent-corresponding to resolution-dependent TEM observations. The method computes GND fingerprints from discretized dislocation line segments extracted from molecular dynamics simulations of dislocation loops being absorbed at a GB. Specifically, we perform MD simulation of prismatic loops of two diameters and monitor the three stages of the absorption process: loop glide, the partial, and full absorption of the loops at a [1 0 0] symmetric tilt GB. These methods provide a framework for future investigations of the nature of defect absorption by grain boundaries under irradiation conditions.