Diffusion in Nanocrystalline Metals and Alloys—A Status Report

Abstract

Diffusion is a key property determining the suitability of nanocrystalline materials for use in numerous applications, and it is crucial to the assessment of the extent to which the interfaces in nanocrystalline samples differ from conventional grain boundaries. The present article offers an overview of diffusion in nanocrystalline metals and alloys. Emphasis is placed on the interfacial characteristics that affect diffusion in nanocrystalline materials, such as structural relaxation, grain growth, porosity, and the specific type of interface. In addition, the influence of intergranular amorphous phases and intergranular melting on diffusion is addressed, and the atomistic simulation of GB structures and diffusion is briefly summarized. On the basis of the available diffusion data, the diffusion‐mediated processes of deformation and induced magnetic anisotropy are discussed.

Atomic Diffusion within Individual Gold Nanocrystal

“…The enhanced diffusion effects have been observed previously from nanocrystal ensembles 29 30 33 . In-situ TEM was applied to study copper diffusion in gold nanocrystal ensemble with average size of 10 nm at room temperature, and the diffusion coefficient was estimated to be at least 9 orders of magnitude higher than the bulk sample 33 .…”

Multifunctional porous catalyst produced by mechanical alloying

“…Also, the 2% oxide alloy forms significant porosity, thereby enhancing available surface area for reaction and break-up. The increased reactivity, then, is consistent with a defectmediated growth mechanism due to enhanced diffusivity in nanocrystalline materials [35] that is aided by in-situ pore formation. Therefore, this multifunctional alloy system allows one-step processing to be used to form and utilize a complex microstructure for efficient catalysis as shown schematically in Figure 4.…”

Absolute concentration of free volume-type defects in ultrafine-grained Fe prepared by high-pressure torsion

“…The latter gives rise to rapid diffusion, much faster than that in conventional grain boundaries, as has been observed in the as-received state prior to structural relaxation in a variety of nanophase metals (for review see Ref. 24), including those prepared by severe plastic deformation [25]. Owing to the direct relation between diffusion and free volumes, excess GB free volume as observed in the present study may be considered as the origin of that enhanced diffusivity.…”