Papers by Author: U. Dahmen

Abstract: Diffusion of nanosized liquid Pb inclusions attached to dislocations in thin aluminum foils was investigated in a wide temperature range using in-situ transmission electron microscopy. Trajectories of motion of the inclusions along the dislocations were used to determine their diffusion coefficients. The temperature and size dependences of diffusion coefficients of the inclusions were obtained. They indicate that (i) studied inclusions hold {111} facets on their surface in the studied temperature range; (ii) the mobility of the inclusions is controlled by step nucleation at the {111} facets.

Abstract: Thermal motion of nanoscale liquid Pb inclusions attached to fixed dislocations in thin Al foils is investigated using in-situ TEM. In contrast with 3D random motion of free inclusions, the attached inclusions demonstrate oscillations in the close proximity of the dislocations. This is due to the elasticity of the dislocations. It is found that inclusions captured by one dislocation repulse at small separations, and attract at large ones and this is also caused by the dislocation elasticity. Such behaviour of trapped inclusions can be considered as a motion in a potential well or in coupled potential wells in the case of motion of several trapped inclusions on one dislocation. The potential of interaction of an inclusion with a dislocation and the potential of mutual interaction between inclusions are determined.

Abstract: We show that it is possible to use high rate co-evaporation of Al and Si onto room temperature substrates to achieve a novel two-phase nanoscale microstructure. These nanocomposites have a hardness as high as 4GPa (Al-23at.%Si), and display noticeable plasticity. Films with compositions of Al-12at.%Si and pure Al (used as baseline) were analyzed using transmission electron microscopy (TEM). The scale of the Al-12at.%Si microstructure is an order of magnitude finer compared to that of pure Al films. It consists of a dense distribution of spherical nanoscale Si particles separating irregularly-shaped small Al grains. These new structures may have a mechanical performance advantage over conventional single phase nanomaterials due to the role of the dispersed hard phase in promoting strain hardening.

Abstract: Diffusion of nano-sized liquid Pb inclusions in thin aluminum foils is investigated using in-situ transmission electron microscopy (TEM). Free diffusion of the inclusions in the bulk and diffusion constrained by dislocations trapping is studied. The motion of trapped Pb inclusions is spatially confined in close proximity to the dislocations. The diffusion coefficients of free motion of the inclusions are determined using Einstein's equation. The diffusion coefficients of trapped inclusions were obtained using an equation based on Smoluchowski's analysis of the Brownian motion of particle in a harmonic potential. The agreement of the diffusion coefficients of free and trapped inclusions indicates the same underlying microscopic mechanism, and no strong influence from dislocations. The microscopic mechanism controlling the mobility is discussed.