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Experimental Observations of Stress-Driven Grain Boundary Migration
My coworkers (Dan Gianola, Yixiang Gan, and Kevin Hemker) and I have published research results in the December 18th, 2009 issue of Science. In this work, we perform tension tests on specially designed thin film samples to studying the influence of different stress and strain states on mechanically-induced grain growth in nanocrystalline aluminum. Our results indicate that shear stresses drive grain boundaries to move in a manner consistent with recent molecular dynamics simulations and theoretical predictions of coupled grain boundary migration.
Our paper can be found at:
http://dx.doi.org/10.1126/science.1178226
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On stress-driven coupling motion of grain boundaries in metals
Dear Tim,
I have recently read your paper and the presentation is generally impressive.
Your have pinpointed that the grain growth phenomena revealed in some
mechanical tests of nanocrystalline metals under athermal loading conditions
is related with shear stress experienced by the grain boundaries. This is a
quite interesting phenomena. However, the underlying mechanisms for this
shear-stress-driven grain boundary migration process is still under debate.
Following the suggestions given by J.W. Cahn (Acta2006), I have done
some atomistic simulations on the shear response of some special
grain boundaries. The following is one of our published result which I
guess you may be interested.
http://iopscience.iop.org/0965-0393/17/4/045008/?ejredirect=.iopsciencet...
Lastly, I have a small question concerning the term 'strain induced' or 'strain driven'
grain growth which you strive to elucidate as the contrary of 'stress driven' grain growth.
Does it mean that grain boundaries migrate under the thermal dynamic driving forces
induced by plastic strain energy (in the form of dislocation density) differences between
neighboring grains developed during deformation process?
Sincerely yours,
L. Wan
Strain as a driving force for GB migration
Hi Liang,
Thank you for your interest in our work. I have not had the chance to fully read your article, but will do so soon since a more complete understanding of the migration mechanism is very important.
The answer to your question is yes, we wanted to conclusively rule out stored plastic strain as a driving force for migration. While this may seem unnecessary since it is becoming well-known that stored dislocation networks do not exist in nanocrystalline materials, it was important to eliminate this common driving force for traditional recrystallization and grain growth as a potential driving force for the growth we observe.
Take care
-Tim Rupert
DOI signature for Liang Wan's article
Hi Liang,
I would recommend adding the DOI signature of your article when placing a link. This kind of link makes it easier for people to find the correct pathway to your work. For example, my institution's subscription service would not let me access your article with the link you had placed.
Liang's article can be found at:
http://dx.doi.org/10.1088/0965-0393/17/4/045008
Sincerely
-Tim Rupert
A great learning!
A great learning! Thanks!
L. Wan