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Title: Mechanism for diffusion induced grain boundary migration

Abstract

Grain boundaries are found to migrate under certain conditions when solute atoms are diffused along them. This phenomenon, termed diffusion induced grain boundary migration (DIGM), has now been found in six systems. The observed phenomenon and empirical data are used to discard certain concepts for the driving force and the mechanism. A mechanism is proposed in which differences in the diffusion coefficients of the diffusing species along the grain boundary cause a self-sustaining climb of grain boundary dislocations and motion of their associated grain boundary steps.

Authors:
;
Publication Date:
Research Org.:
Massachusetts Inst. of Tech., Cambridge (USA); National Bureau of Standards, Washington, DC (USA). Center for Materials Science
OSTI Identifier:
5013063
Report Number(s):
DOE/ER/05002-13
DOE Contract Number:
AS02-78ER05002
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; METALS; GRAIN BOUNDARIES; CRYSTAL STRUCTURE; ELEMENTS; MICROSTRUCTURE; 360102* - Metals & Alloys- Structure & Phase Studies

Citation Formats

Balluffi, R.W., and Cahn, J.W. Mechanism for diffusion induced grain boundary migration. United States: N. p., 1980. Web. doi:10.2172/5013063.
Balluffi, R.W., & Cahn, J.W. Mechanism for diffusion induced grain boundary migration. United States. doi:10.2172/5013063.
Balluffi, R.W., and Cahn, J.W. 1980. "Mechanism for diffusion induced grain boundary migration". United States. doi:10.2172/5013063. https://www.osti.gov/servlets/purl/5013063.
@article{osti_5013063,
title = {Mechanism for diffusion induced grain boundary migration},
author = {Balluffi, R.W. and Cahn, J.W.},
abstractNote = {Grain boundaries are found to migrate under certain conditions when solute atoms are diffused along them. This phenomenon, termed diffusion induced grain boundary migration (DIGM), has now been found in six systems. The observed phenomenon and empirical data are used to discard certain concepts for the driving force and the mechanism. A mechanism is proposed in which differences in the diffusion coefficients of the diffusing species along the grain boundary cause a self-sustaining climb of grain boundary dislocations and motion of their associated grain boundary steps.},
doi = {10.2172/5013063},
journal = {},
number = ,
volume = ,
place = {United States},
year = 1980,
month = 8
}

Technical Report:

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  • The recently recognized phenomenon of diffusion-induced grain-boundary migration has been systematically investigated to determine conditions under which this effect occurs and to establish the mechanism and driving forces that control this process. This migration and the surface alloying that accompanies it were observed in a number of different alloy systems, including Cu-Zn, Cu-As, Au-Pd, Fe-Zn, Fe-Cr, and Fe-As. Detailed tests in the Ag-Au alloy system using thin layers of diffusant deposited on a metal substrate and analyses of liquid phase sintering experiments in Mo-Ni base alloys indicated that the driving force for diffusion-induced grain-boundary migration depends on lattice-parameter variations inmore » the alloy. Connections were made between diffusion-induced grain-boundary migration in solid alloy systems and liquid-film migrations that occur during liquid-phase sintering. A coherency stress theory proposed by Hillert was extended to provide predictions concerning these effects. This theory then was used to select ceramic systems in which migrations might occur and, as a result, diffusion-induced liquid-film migration was observed for the first time in a ceramic system.« less
  • While grain boundaries and interphase boundaries provide high diffusivity paths in solids, little bulk composition change can occur at temperatures where lattice diffusion is frozen out unless the boundaries migrate. That the diffusion itself can induce boundary migration has been suspected for some time. This study reviews evidence that the effect is indeed common, and this conclusion is reinforced by additional observations on three systems. (GHT)
  • Diffusion induced grain boundary migration (DIGM) was studied by transmission electron microscopy and scanning transmission electron microscopy in the gold-rich layer of thin film Au/Cu and Au/Ag diffusion couples posessing grain boundary structures of controlled geometry. When either copper or silver was diffused along the boundaries in the gold-rich layer at temperatures where lattice diffusion was essentially frozen out, the boundaries were induced to migrate leaving alloyed zones behind in their wakes. The structures and compositions of the alloyed zones and the kinetics of the migration under various conditions were studied in detail in a large number of (111) andmore » (001) tilt boundaries in Au/Cu couples and (111) tilt boundaries in Au/Ag couples. The phenomenon was also studied more indirectly by Auger sputter depth profiling ar random boudaries in Au/Ag couples.« less
  • Analytical electron microscopy results are reported for a series of vanadium alloys irradiated in the HFIR JP23 experiment at 500{degrees}C. Alloys were V-5Cr-5Ti and pure vanadium which are expected to have transmuted to V-15Cr-5Ti and V-10Cr following irradiation. Analytical microscopy confirmed the expected transmutation occurred and showed redistribution of Cr and Ti resulting from grain boundary migration in V-5Cr-5Ti, but in pure V, segregation was reduced and no clear trends as a function of position near a boundary were identified.
  • It is currently well established that the fast self-diffusion which occurs along grain boundaries (GBs) in metals must occur by a point defect exchange mechanism. For example, it is known that rapid GB diffusion can transport a net current of atoms along GBs during both sintering and diffusional creep, and that the two species in a binary substitutional alloy diffuse at different rates in GBs. However, it has not been possible to establish firmly whether the defect mechanism involves the exchange of atoms with vacancy or interstitial point defects. It has been suspected that the vacancy exchange mechanism must applymore » but it has been difficult to prove this hypothesis because of a lack of detailed information at the atomistic level. The results are presented of an effort to establish the GB self-diffusion mechanism in a bcc iron ..sigma.. = 5 (36.9/sup 0/) (001) (310) tilt boundary using the combined methods of computer molecular statics and molecular dynamics simulation.« less