Formation Of Interstitial Atoms Research Articles

Particularities of the interstitial atoms and vacancies clusters formation in a thin cadmium telluride foil during in situ electron irradiation in a TEM

The formation of interstitial atoms and vacancies, as well as their clusters in the form of dislocation loops and voids in CdTe is simulated. The sizes and features of the growth of dislocation loops and voids were determined depending on the irradiation time, taking into account the decrease in the number of nodes of the semiconductor crystal lattice with the irradiation time, since in experiments we studied a thin CdTe foil in a transmission electron microscope (TEM). The calculated and experimental data are compared.

Effect of addition of micron-sized lanthanum oxide particles on morphologies, microstructures and properties of the wire laser additively manufactured Ti–6Al–4V alloy

The bead geometry, microstructure and mechanical properties of wire laser additively manufactured (WLAM) Ti–6Al–4V samples reinforced by different contents of micron-sized lanthanum oxide (La2O3) particles were explored. The images attained through high-speed charge coupled device (HCCD) and metallographs showed that the addition of La2O3 changed the morphologies of the weld bead of Ti–6Al–4V alloy to lead to the significant reduction of the width of the deposited weld bead and remarkable growth of the weld penetration. The observation result attained through the scanning electron microscope (SEM) revealed that relative to the condition without the addition of micron-sized La2O3 particles, nano-sized La2O3 particles were uniformly distributed in the matrix after adding micron-sized La2O3 particles; β grains and α phases were both greatly refined. Compared with the primitive La2O3 powders, the morphology of La2O3 in the matrix approximately presented a spherical shape. It indicated that La2O3 particles in the molten pool partly or completely decomposed during WLAM. The dispersedly distributed nano-sized La2O3 particles induced fine grain strengthening and dispersion strengthening. Therefore, the tensile strength and Vickers hardness of the deposit of the Ti–6Al–4V alloy rose with increasing addition amount of La2O3. However, the decomposition of La2O3 particles resulted in the formation of interstitial atoms (such as interstitial O atoms), thus leading to the decrease of the elongation of deposits. Without the addition of La2O3 particles, the deposit of the Ti–6Al–4V alloy fractured in the large-size lamellar α during the tensile test, in which the fracture showed micro-morphology of ductile fracture. After the addition of La2O3 particles, the deposit of Ti–6Al–4V alloy fractured at the grain boundary α phase during the tensile test and both cleavage and ductile morphologies were found at the fracture.

FEATURES OF HELIUM COMPLEXES BEHAVIOUR NEAR THE FREE SURFACE IN TUNGSTEN

The formation of interstitial atoms by lattice tungsten atoms displacement by clusters of implanted helium, which is accompanied with the appearance of helium-vacancy complexes, was found. The stimulating effect of the free surface on the development of the processes of displacement and dissociation of complexes has been revealed. It is shown that this influence is caused by the action of image forces. The depth of the image forces was determined, which was about 2.5 nm.

Influence of electrostatic field treatment on microstructures and mechanical properties of GH4169 superalloy

An external electrostatic field treatment (EFT) was applied to GH4169 alloy with standard heating treatment. The internal friction and room temperature (RT) tensile test were conducted for both the electrostatic field treated and standard heating treated alloys in order to investigate the variations of microstructure and mechanical properties of the alloy with the EFT. The experimental results demonstrated that the EFT remarkably enhanced the formation of interstitial atoms and vacancies. During the tensile deformation at RT under the strain rate of 10−2 or 10−4 s−1, the dislocation slip could be evidently hindered by the large numbers of interstitial atoms in the matrix, contributing to a great increase in the yield and tensile strengths of the electrostatic field treated alloy. By EFT, the dislocation configuration of deformed alloy was primarily the single slip instead of the cross-slip in the standard heating treated alloy, resulting in the increasing of grain deformation capacity by more vacancies.

Formation of interstitial atoms in surface layers of helium-implanted tungsten

Using a method of field ion microscopy, the atomic structure of surface and near-surface layers of a perfect dislocation-free tungsten irradiated by helium ions with energies below the threshold of displacement was studied. We have found the output of tungsten atoms from the bulk as a result of their displacement from regular lattice positions occupied by implanted helium atoms and the formation of interstitial tungsten atoms. It is shown that high concentrations of helium and the presence of image forces have a considerable effect on the development of these processes. Depleted zones consisting of helium-vacancy complexes are revealed within the irradiated near-surface layer.

Comments on the paper of V. L. Gapontsev and V. M. Koloskov “Nonequilibrium vacancy-stimulated diffusion (induced diffusion) as the main mechanism of activated alloy formation”

The authors of the considered paper in their study are focusing on systems of metal phases that can be called substitution phases. Presumably, in this case a variation of the mixture composition in the course of reaction is of less significance, since here in diffusion we observe point defects of the same sort (vacancies). It would be interesting to investigate the diffusion of interstitial atoms for some real objects. Due to the low values of diffusion activation energy for interstitial atoms, we could expect an improved sensitivity of the methods to composition variation (a higher diffusion coefficient). In any case it appears necessary to discuss the role of interstitial atoms in the preservation of the vacancy concentration with respect to annihilation processes. It follows from the theory proposed by V. Indenbom and A. Orlov that plastic deformation under low temperatures and significant loads, which are typical for high-energy mills, leads to the formation of interstitial atoms. The considered paper gives several examples of the practical use of mechanochemical synthesis. It would be important for the description of particular examples to include all parameters of synthesis, as well as selection, calculation of quantities, and methods of introduction of material, in particular, for so-called nonequilibrium vacancies. Below are certain considerations regarding the state of an activated alloy.

Mechanism of low-temperature ion-bombardment-activated surface self-diffusion

Elementary events of low-temperature surface erosion induced by the bombardment with accelerated helium atoms and ions were studied at the atomic level. It is established that the regular arrangement of surface atoms is disturbed due to the release of energy of formation of interstitial atoms emerging at the surface and to the expenditure of part of this energy on the formation of surface defects in excited states. The adatom excitation energy allowing the short-range diffusion processes was determined experimentally.

Effect of hydrogen on formation of interstitial atoms in iron

Effect of hydrogen on formation of interstitial atoms in iron