Grain Boundary Radiotracer Diffusion of Ni in Ultra-Fine Grained Cu and Cu - 1wt.% Pb Alloy Produced by Equal Channel Angular Pressing

2008 ◽  
Vol 584-586 ◽  
pp. 380-386 ◽  
Author(s):  
Jens Ribbe ◽  
Guido Schmitz ◽  
Y. Amouyal ◽  
Yuri Estrin ◽  
Sergiy V. Divinski
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Equal Channel Angular Pressing ◽  
Boundary Diffusion ◽  
Ion Beam ◽  
Short Circuit ◽  
Grain Boundary Diffusion ◽  
Coarse Grained ◽  
Angular Pressing ◽  
Diffusion Paths

The radiotracer technique was applied for measuring grain boundary diffusion of Ni in ultrafine grained (UFG) copper materials with different nominal purities and in a Cu—1wt.%Pb alloy. The UFG specimens were prepared by equal channel angular pressing at room temperature. The stability of the microstructure was studied by focused ion beam imaging. Grain boundary diffusion of the 63Ni radioisotope was investigated in the temperature interval from 293 to 490K under the formal Harrison type C kinetic conditions. Two distinct short-circuit diffusion paths were observed. The first (relatively slow) path in the UFG materials corresponds unambiguously to relaxed high-angle grain boundaries with diffusivities which are quite similar to those in the respective coarse-grained reference materials. The second path is characterized by significantly higher diffusivities. The experimental data are discussed to elucidate the contribution of nonequilibrium grain boundaries in the deformed materials. Alternative contributions of other shortcircuit diffusion paths cannot be ruled out, particularly for the Cu-Pd alloy.

Effect of Equal Channel and Dynamic Channel Angular Pressing of Ni and Further Heat Treatment on its Structure and Grain Boundary Diffusion

2018 ◽  
Vol 383 ◽  
pp. 96-102 ◽  
Author(s):  
Vladimir V. Popov ◽  
Gerrit Reglitz ◽  
Evgeniy V. Shorohov ◽  
E.N. Popova ◽  
Alexey V. Stolbovsky ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Boundary Diffusion ◽  
Grain Boundary Diffusion ◽  
Coarse Grained ◽  
Internal Stresses ◽  
Angular Pressing ◽  
Dynamic Channel Angular Pressing ◽  
Dynamic Channel ◽  
Non Equilibrium

Formation of microstructure in Ni under equal-channel angular pressing (ECAP) and dynamic channel-angular pressing (DCAP), its thermal stability and diffusion properties of grain boundaries are investigated. Grain boundary diffusion in the ultrafine-grained Ni is found to be significantly faster than in the coarse-grained Ni, which indicates a 'non-equilibrium' (deformation-modified) state of grain boundaries in the former. The effect of non-equilibrium state of grain boundaries on the level of internal stresses is analyzed.

Grain Boundary Diffusion in Recrystallizing Nanocrystalline Materials

2009 ◽  
Vol 289-292 ◽  
pp. 641-648 ◽  
Author(s):  
Leonid Klinger ◽  
Y. Amouyal ◽  
Sergiy V. Divinski ◽  
Eugen Rabkin
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Equal Channel Angular Pressing ◽  
Diffusion Coefficients ◽  
Nanocrystalline Materials ◽  
Boundary Diffusion ◽  
Grain Boundary Diffusion ◽  
Ultrafine Grain ◽  
Angular Pressing

A model that considers diffusion in nanocrystalline materials undergoing recrystallization was developed. Application of this model enabled us deriving 63Ni radiotracer diffusion coefficients along the grain boundaries in ultrafine grain copper produced by equal channel angular pressing from the experimentally measured radiotracer penetration profiles.

Grain Boundary Diffusion of Hydrogen in Nano-Structured Pd/Ag Alloy Membranes

2008 ◽  
Author(s):  
Logan S. McLeod ◽  
Levent F. Degertekin ◽  
Andrei G. Fedorov
Keyword(s):  
Grain Boundary ◽  
Diffusion Process ◽  
Grain Boundaries ◽  
Boundary Diffusion ◽  
Grain Boundary Diffusion ◽  
Coarse Grained ◽  
Appreciable Amount ◽  
Bottom Surface ◽  
Fast Diffusion ◽  
Average Grain Size

Palladium and its alloys have long been used as hydrogen separation membranes due to their extremely high permeability and selectivity to hydrogen over all other gases [1]. The hydrogen permeation process begins with selective chemisorption of the gas onto the metal surface. As the adsorption process is the point in the permeation sequence where the majority of gases become excluded, it follows that a cleverly designed device could be created to take advantage of the so-called ‘fast’ diffusion paths of surface and grain-boundary diffusion to further enhance permeability without sacrificing selectivity. The contribution of grain-boundary diffusion to the overall permeation rate is dependent on the relative volume in the membrane occupied by grain-boundaries versus bulk material. Typically, grain boundaries only make up a miniscule fraction of the overall volume and therefore only contribute an appreciable amount to the overall diffusion process at temperatures low enough to make the bulk diffusion process nearly stagnant. However, in the case of a nanostructured membrane this paradigm is no longer valid. The fabrication methods associated with extremely thin membrane deposition typically lead to highly non-equilibrium microstructure with an average grain size on the order of tens of nanometers [2]. In order to exploit the potential advantages of grain boundary diffusion the nano-scale grains must persist throughout operation. To avoid the tendency for the grain structure to relax to a more equiaxed, coarse-grained morphology the self-diffusion of metal atoms in the film must be minimized by operating the membranes at a temperature much lower than the membrane melting temperature. Figure 1 shows the microstructural changes in a thin, sputtered, Pd/Ag alloy film before and after annealing. The initial fine-grained structure on the bottom surface of the membrane is due to a combination of low substrate temperature during deposition and the Ti adhesion layer onto which the Pd/Ag layer was deposited. After annealing at 400 C the grains have coarsened and the top and bottom structure are identical.

Application of Nuclear Gamma-Resonance Spectroscopy for Determination of Grain-Boundary Diffusion Characteristics and the State of Grain Boundaries

2019 ◽  
Vol 391 ◽  
pp. 201-214
Author(s):  
Vladimir V. Popov
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Boundary Diffusion ◽  
Grain Boundary Diffusion ◽  
Coarse Grained ◽  
Resonance Spectroscopy ◽  
Diffusion Parameters ◽  
Ultrafine Grained ◽  
Ultrafine Grained Materials

Capabilities of application of Mössbauer spectroscopy for determination of grain-boundary diffusion parameters in coarse-grained and ultrafine-grained materials have been analyzed. Application of this method for revealing of non-equilibrium state of grain boundaries in ultrafine-grained materials obtained by severe plastic deformation is demonstrated.

Modern Models of Grain Boundary Diffusion

2011 ◽  
Vol 312-315 ◽  
pp. 1116-1125
Author(s):  
Vladimir V. Popov
Keyword(s):  
Plastic Deformation ◽  
Grain Boundary ◽  
Severe Plastic Deformation ◽  
Nanocrystalline Materials ◽  
Boundary Diffusion ◽  
Grain Boundary Diffusion ◽  
Coarse Grained ◽  
Gas Condensation ◽  
Non Equilibrium

Recent models of grain-boundary diffusion are briefly reviewed. Models of diffusion along equilibrium boundaries of recrystallization origin in coarse-grained materials and along non-equilibrium boundaries in nanocrystalline materials obtained by gas condensation and compacting or by severe plastic deformation are considered separately.

Grain Boundary Diffusion and Segregation in the Solid State Phase Transformations

1998 ◽  
Vol 527 ◽  
Author(s):  
E. Rabkin ◽  
W. Gust
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Boundary Diffusion ◽  
Grain Boundary Diffusion ◽  
Solute Diffusion ◽  
Apparent Difference ◽  
Impurity Drag ◽  
The Difference ◽  
Boundary Width ◽  
Dynamic Segregation

ABSTRACTWe consider the problem of solute diffusion and segregation in the grain boundaries moving during a phase transformation in the framework of Cahn's impurity drag model. The concept of a dynamic segregation factor for the diffusion along moving grain boundaries is introduced. The difference between static and dynamic segregation factors may cause the apparent difference of the triple product of the segregation factor, grain boundary width and grain boundary diffusion coefficient for stationary and moving grain boundaries. The difference between static and dynamic segregation is experimentally verified for the Cu(In)-Bi system, for which the parameters of static segregation are well-known. It is shown that the complications associated with the dynamic segregation may be avoided during the study of the discontinuous ordering reaction. From the kinetics of this reaction, the activation energy of the grain boundary self-diffusion can be determined.

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