September 17th Twinning Meeting

In reality, the twinning meeting was more or less a continuation of the grain boundary engineering meeting from last Friday. Yuan and I met up with Nathalie first to go over the questions that we want answered. This focused on two major aspects in the field of annealing twins:

• What do twins look like in 3-D? What morphological categories can we associate them with?
• Do twins occur with recrystallization or with grain growth? And what influence does GB velocity as well as curvature have in that case?

These questions lack the answers primarily due to lacking data, but also conflicting data. In most cases of the first, only the recent tools have come about in allowing us to find the answers we desire. These involve both high energy x-ray diffraction microscopy (HEDM) as well as the serial sectioning combined with EBSD/FIB. The case of the latter arises simply due to the fact that the original experiment premise wasn't designed for such an investigation of twinning. A primary issue that comes from grain sizes varying far too much as a result of the annealing procedures, where it has been clearly shown that grain size does play a role to twin density.

Tony arrived a little later, at which point we were going over the data we presently have all together. This includes previous work on Stainless Steel 304L, Inconel 718 (both provided by CEMEF), as well as the work on high purity nickel and nanocrystalline nickel (done at CMU). This is important in determining the next steps that we take, that is, what is it that we're trying to find out, primarily in the three weeks that Yuan is here in Pittsburgh.

We've currently concluded with two goals:

1. Develop a 3-D data set via serial sectioning (by vibromet) and EBSD to confirm the morphology of twins (at a high resolution) in either 304L or Ni
2. Streamline and unify our data from both CMU and CEMEF such that we can actually compare out values to one another, and produce a stronger overall report on what we know

I'm slowly finding out that while such research meetings feel very time-consuming and exhaustive, they are definitely very helpful in focusing on the topics of interest. Whereas some of my prior work seems to have been all over the place without a clear goal necessarily. The next few weeks will definitely be busy, but also very rewarding.

On another note, after three days of work, my code to obtain all boundaries of recrystallized grains (those including the border between recrystallized and deformed grains) now works. The next step is cleaning up the code to something... more bearable for the next user