iMechanica - metal thin film - Comments

Sorry for the late reply.

Ying Li — Tue, 24 Jun 2008 04:56:10 -0400

Sorry for the late reply. EBSD is a good method to monitor the texture of the film. By the EBSD, the grain size of the Cu could be clearly investigated. Especially, the in-situ SEM loading with the EBSD could check the grain growth when the Cu film is under tension. Such a in-situ SEM with EBSD method has been successfully applied to investigate the equal channel angular extruded Mg-3Al-Zn magnesium alloy. However, as you say, the indexing rate is very low for nano grains.

Ying Li Department of Engineering Mechanics Tsinghua University Beijing, 100084, P. R. CHINA

The size effect on failure modes of metal thin films

Nanshu Lu — Thu, 12 Jun 2008 13:26:26 -0400

Hi, Teng,

Thanks for pointing this out. Actually it is what I am doing now.

Basically the film failure mode exhibits a ductile-brittle transition as film thickness reduces. But we found that neither the thickness nor the grain size alone will be sufficient to understand the phenomenon. I am trying to take both factors into consideration to give better explanations now.

I'll send you some preliminary results through email.

Nanshu

Difficulty with grain size distribution

Nanshu Lu — Thu, 12 Jun 2008 13:10:00 -0400

Ying, thanks for your interest and comment.

We haven't found any efficient way to determine the statistical distribution of nano grains so that we are trying to show straightforward micrographs at this point.

TEM is not suitable because the film microstructure is very unstable and easy to change during sample preparation.

EBSD works well for annealed films with micron-sized grains but the indexing rate is very low for nano grains.

XRD does not show much broadening because our grain size is not small enough.

I will try AFM to see if it can give reasonable results.

Manually sketching grain boundaries will always work but I will keep it as the last choice.

Do you have any experience or suggestions on this to share with us? Many thanks.

Nanshu

Effect of film thickness

Teng Li — Thu, 12 Jun 2008 11:08:49 -0400

Nanshu,

Neat experiments! The paper reveals another critical mechanism governing the failure of metal films on polymer substrates.

The films reported in paper are about 1 micron thick. I'm curious about the effect of film thickness on the deformation-induced grain growth. For example, does similar phenomenon occur in a thinner film (say, a few hundred nm thick) on a polymer substrate.

Interesting work!

Ying Li — Thu, 12 Jun 2008 08:26:24 -0400

Have you done the detailed work on the grain size distribution according to your SEM or FBI imagines? I think the statistical data may be more helpful to understanding the deformation-induced grain growth.

Ying Li Department of Engineering Mechanics Tsinghua University Beijing, 100084, P. R. CHINA