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 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.

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.

Numerical Study of Grain Boundary Diffusion in Nanocrystalline Materials

2005 ◽  
Vol 237-240 ◽  
pp. 1043-1048 ◽  
Author(s):  
D. Gryaznov ◽  
J. Fleig ◽  
Joachim Maier
Keyword(s):  
Grain Boundary ◽  
Nanocrystalline Materials ◽  
Boundary Diffusion ◽  
Nanocrystalline Material ◽  
Numerical Study ◽  
Average Length ◽  
Type A ◽  
Grain Boundary Diffusion ◽  
Conventional Models ◽  
Diffusion Profiles

Diffusion in nanocrystalline materials is becoming an increasingly important topic. The analysis of diffusion profiles obtained in nanocrystalline materials with enhanced grain boundary diffusion, however, is not straightforward since assumptions made in the deviation of the conventional models are often not fulfilled. In this contribution numerical diffusion studies are performed in order to investigate effects caused by the high density of interfaces in nanocrystalline material. A continuum model based on the 2D 2-nd Fick’s law was solved by means of the finite element method. This allows us to analyze diffusion profiles for different geometrical situations such as a single boundary, square grains with the grain size of 80 nm and 25 nm and geometries comprising differently oriented boundaries of the average length of 30 nm . The analysis was carried out for different diffusion lengths corresponding to Harrison type A and type B kinetic regimes. For the isolated boundary a very good agreement was achieved in comparison with the classical Whipple’s solution. For nanocrystalline material, however, considerable errors can occur when analyzing the averaged diffusion profiles in the conventional Harrison type A and B kinetics.

scholarly journals Effect of Deformation Structure and Annealing Temperature on Corrosion of Ultrafine-Grain Fe-Cr Alloy Prepared by Equal Channel Angular Pressing

2018 ◽  
Vol 2018 ◽  
pp. 1-15
Author(s):  
Muhammad Rifai ◽  
Motohiro Yuasa ◽  
Hiroyuki Miyamoto
Keyword(s):  
Grain Boundaries ◽  
Equal Channel Angular Pressing ◽  
Annealing Temperature ◽  
Surface Region ◽  
Passivation Layer ◽  
Ultrafine Grain ◽  
Deformation Structure ◽  
Early Stages ◽  
Angular Pressing ◽  
The Stability

The effect of the deformation structure and annealing temperature on the corrosion of ultrafine-grain (UFG) Fe-Cr alloys with 8 to 12% Cr prepared by equal channel angular pressing (ECAP) was investigated with particular emphasis on the stability of the passivation layer. Fe-Cr alloys were processed by ECAP using up to eight passes at 423 K by the Bc route, followed by annealing at temperatures of 473 to 1173 K for 1 h. Passivity appeared in all alloys as a result of ECAP, and the stability of the passivation layer was evaluated by anodic polarization measurements in a 1000 mol·m−3 NaCl solution. The stability of the passivation layer increased as the degree of deformation became more extensive with successive ECAP passes, and distinct escalation occurred with the formation of a UFG microstructure. In the early stages of annealing at moderate temperatures, the stability of the passivation layer deteriorated, although no visible grain growth occurred, and this effect increased monotonically with increasing annealing temperature. The high degree of stability of the passivation layer on UFG alloys following ECAP can be attributed to the large number of high-angle nonequilibrium grain boundaries, which may lead to Cr enrichment of the surface region. The deterioration of the passivation layer in the early stages of annealing may be attributed to a change in the grain boundaries to an equilibrium state. The present results show that the superiority of as-ECAPed materials of the Fe-Cr alloy to recovered ones by heat treatment can be achieved with 8–10% Cr as observed in 20% Cr.

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