Migration Of Solute Atoms Research Articles

Atomic Pathways of Solute Segregation in the Vicinity of Nanoscale Defects.

Using GeSn semiconductor as a model system, this work unravels the atomic-level details of the behavior of solutes in the vicinity of a dislocation prior to surface segregation in strained, metastable thin layers. The dislocations appear in the 3D atom probe tomography maps as columnar regions, 3.5-4.0 nm wide, with solute concentrations 3-4 times higher than the sounding matrix. During the initial stage of phase separation, the migration of solute atoms toward the dislocation is associated with a gradual increase in Sn concentration and in density of atomic clusters, which reach 175-190 per 103 nm3 with 12-15 atoms/cluster close to dislocations. The latter provide, at advanced stages, fast diffusive channels for Sn mass-transport to the surface, thus bringing the matrix around the dislocation to the equilibrium concentration. In parallel, an increase in solute concentration (∼0.05 at. %/nm) and in the number of atomic clusters (12-16 clusters/33 nm) is observed along the dislocation core.

A study on the early-stage decomposition in the Al–Mg–Si–Cu alloy AA6111 by electrical resistivity and three-dimensional atom probe

Electrical resistivity measurements and three-dimensional atom probe (3DAP) analysis were employed to investigate early-stage decomposition of the Al alloy AA6111 in the temperature range 60–180°C where electrical resistivity initially increased with ageing time. 3DAP measurements provided information on the shape, number density and solute content of the precipitates, as well as the solute concentration of the matrix, for the ageing conditions corresponding to the resistivity maxima. Using the 3DAP results, the precipitate size distributions for these ageing conditions were determined in terms of the measured number of solute atoms per precipitate. The number density and the Cu content of the precipitates decreased with increasing temperature, whereas the Mg/Si ratio increased. The size distribution of precipitates at the higher ageing temperatures showed the addition of larger size precipitates to the precipitate population. A modification to Matthiessen's law was employed to describe the anomalous resistivity increase by considering the effect of solutes and precipitates on the resistivity evolution. Using the 3DAP results in analysing the resistivity anomaly, it was found that the decrease in the resistivity maxima with increasing temperature was associated with the decrease in the number density of precipitates and not the scattering power of precipitates. The 3DAP results were further used to provide information on the mechanisms of early-stage decomposition and the temperature dependence of the nucleation rate. From this, the nucleation rate appeared to be controlled by the migration of solute atoms, which was assisted by quenched-in vacancies.

The Migration of Solute Atoms in the Stress Field of a Slowly Moving Crack

The stress-driven diffusion of solute atoms to a slowly moving brittle crack is studied under the condition of pure drift. The first-order drift-diffusion equation for a slowly moving crack at uniform velocity is solved yielding the flow lines and the impurity segregation rate in terms of the crack growth rate. The flow line patterns reveal important insights with respect to the solute migration kinetics near a steadily advancing subcritical crack at stage I and stage II crack growth.

The segregation of copper and silicon in Al-Si-Cu alloy during electromagnetic centrifugal solidification

The present paper investigates the segregation of copper and silicon in an Al–lwt%Cu–lwt%Si alloy solidified under the co-action of centrifugal and electromagnetic forces. The reasons for the solute segregation and the effect of electromagnetic force on segregation are discussed. Tubular samples cut from the solidified alloy are analyzed, the results showing that the segregation of copper and silicon occurs along the normal direction of the samples and that the electromagnetic field has a remarkable influence on the segregation of both copper and silicon. As the exciting current increases, the segregation of copper decreases, while the segregation of silicon first increases and then decreases. The migration of solute atoms in the melt depends not only on the density difference between the solute and aluminum atoms, but also on the strength of the electromagnetic force. The magnetic force changes the rotation velocity of the melt, reduces the migration velocity of copper and causes the reduction of copper segregation. Because of the difference of the electrical conductivity between the solute and the aluminum melt, the reductions of velocity are not equal.

Theory of Nonlinear Anelastic Internal Friction Peaks. I. The Migration of Solute Atoms in Dislocation Core

Based on the kink model, the diffusion mode of the solute atoms situated at the kink and at the extremities of the kink was analyzed. The probability density or the distribution function of a solute atom at the position (x, y) on a kink chain was formulated. This distribution function changes atom at the position (x, y) on a kink chain was formulated. This distribution function changes when the kink chain moves under an applied stress. The change of the total energy of the kink chain was calculated and thus the transverse and the longitudinal forces acted upon the solute atom. The equations of the longitudinal and transverse core diffusion of the solute atom were formulated accordingly.

Study of the Superconducting Transition Temperature in Dilute Thallium Solid Solutions

The superconducting transition temperature, T/sub c/, has been measured for dilute solid solutions of indium, bismuth, and lead in thallium. The transition temperature is found to increase in all cases thus exhibiting a behavior opposite to that observed by Serin, Lynton, and co-workers in their studies of solid solutions of tin, indium, and aluminum. Some loss in residual impurity scattering which occurs upon annealing suggests the migration of solute atoms to grain boundaries in the dilute alloys. (auth)