Month: January 2014

Taking OIM Analysis To Heart

Matt Nowell
EBSD Product Manager, EDAX

One of the fun perks of working at EDAX is the easy availability of scientific characterization equipment. I’ve had Scout groups in to look at bugs and Velcro with SEM imaging and have helped science projects along by looking at the chemistry of the lettering on M&M candy and the change in composition of coins as a function of time. A few years ago though I had the opportunity to analyze something very near and dear to my heart, and to my son’s.

My youngest son Finn was a micro-premie, born at only 23 weeks gestation. He was just over 12” long and weighted 770 grams. Obviously his care at this stage required a great deal of medical care and intervention. One of the complications he experienced is termed Patent Ductus Arteriosus (PDA), where a portion of the heart fails to close after birth. For Finn, the treatment was to close the dutus arteriosus surgically using a small clip, and this is where the microstructural characterization story starts to get interesting.

After the surgery, the doctor came in to explain the procedure. He positions a small piece of titanium wire around the DA, and clips it shut to close it. He also had a few of the clips attached to a little gauze pad to show us. They looked pretty much like half of a staple, and in essence that is exactly what they are. I asked him if I could keep the samples, and he agreed. I did not look at the Explanation of Benefits though to know if I was charged for them.

I took a clip, polished it up for OIM work, and put it in the SEM. The first dataset I collected was using ComboScan to image the entire clip. Here is the resulting combined image quality and orientation map (IQ + IPF), covering roughly a 5 mm by 1.5 mm area, with a 2.5 µm step size:

Matt_Fig 1

Satisfied I was getting data, I focused my attention on the bend region, where I expected microstructural changes to occur due to the bending. This dataset covered a 390 µm x 403µm area with a 300 nm step size to better resolve the microstructural detail. The resulting IQ + IPF map looks like this:

IQ + IPF map

This data provides a lot of information as to what is happening in the material during the bending process. When the wire is bent, the inner diameter (right hand side of the image) is put into compression while the outer diameter (left hand side) is put into tension. These localized stress states cause permanent or plastic deformation, which results in a shape change of the material. This plastic deformation can be measured using a Local Orientation Spread (LOS) metric within our OIM Analysis software. The LOS image is shown here:

The LOS image

In the LOS image, the plastic deformation levels are plotted on a thermal scale, where the regions of lower LOS are colored blue, and as LOS values increase the coloring becomes warmer into the yellows and reds. The inner diameter stressed in compression has the greatest LOS field, while the outer diameter in tension also shows some higher LOS values. These higher LOS values would suggest that at least some of the deformation induced during bending is accommodated by the formation of dislocations, which manifest themselves as the small orientation rotations measured by the LOS metric. Click here for more information about LOS and measuring plastic strain with EBSD.

EBSD and OIM is especially useful for characterizing grain boundary structure, and this example is no exception. Here is the misorientation angle distribution for the bend area map:

Misorientation angle distribution for the bend area map

The red line shows the measured misorientation distribution while the blue line shows the distribution expected for a random set of titanium measurements. Clearly there is some preference for specific grain boundary misorientations. OIM Analysis provides some nice tools to investigate this. First I will plot only the misorientations between 50° and 90°.

Specific grain boundary misorientations between 50° and 90°The highest peaks can then be selected and colored.

The highest peaks can then be selected and coloredFinally, this color coding can be applied to any of the maps in OIM Analysis. Here I have selected an image quality map for this interactive highlighting:

An image quality map for this interactive highlighting

Here we can see the spatial distribution of these specific grain boundaries, with some correlation with the regions of higher stress and strain. Typically these peaks of misorientations are either evidence of phase transformations or twinning. In this case, it is expected that these are twin boundaries that are introduced into the material during bending.

In the end, I did not learn too much about the material that I did not expect. When you apply enough force to something, my expectation is that it will either bend or break. As a microstructural characterization guy, I am happy to see measurable data showing regions that bent. As a father, I am happy to see a material that works as designed. Once in a while when we are at the hospital for some follow up visit, I keep my eye out for the surgeon, ready to tell him his excellent choice of material and strain rate, feeling confident I have the data to back that up.

Crystals, Chemistry and Christmas Trees

Tara Nylese
Global Applications Manager, EDAX

The break before the new year is an excellent opportunity to have some fun “playing” in the lab, which makes it an even better time to start EDAX’s first blog.

A few days into the holiday break, my 10 year old daughter and I opened up a ‘grow your own Christmas tree’ package that we bought at the dollar store. I didn’t realize it at the time, but I was about to conduct a grade school level science experiment, except this time, with access to my scanning electron microscope and x-ray system. Out of my usual chemistry inquisitiveness I looked for an ingredients list. I was disappointed not to see what it contained so that I could anticipate what was to happen when we started mixing.

We placed the cardboard tree in the stand and added the special fluid packet. Within a few minutes we noticed the capillary action drawing the fluid up through the tree, but that didn’t really keep our interest so we went about doing something else. A few minutes later, we were amazed to suddenly see that our tree had in fact sprouted crystals. My daughter described it well, if not scientifically, when she said that it looks like mold. I, however, took a closer look, and you can too.

"Magic" Christmas tree

After a few more minutes we lost interest altogether until the next morning when I stopped in my tracks upon seeing the full grown tree.

Potassium crystals growing on 'magic' tree

My next thought was, “I wonder what this is” and I recalled a joke from an old friend, Bob, who often said that ‘we have ways to figure that out’.

During the week I was off, I used my best guesses to decide what it may be. My original thought on the chemistry was Magnesium Sulfate, but then I also got to thinking about the microstructure of the crystals. A quick google search had me rethinking my first idea since the structure didn’t line up. So finally I got to pack my ziplock bag and bring my sample in to work.

The first SEM images I gathered were just beautiful to me. A grown crystal is perfection and this was a classic example. The tragedy was in the delicacy and it was hard to find an area that contained long repeating and unbroken crystals. The images show dense areas of crystals and also areas looser on the carbon tape.

Potassium phosphate crystal needlesPotassium phosphate crystal needles

 A quick 10 second spectrum showed these to be a Potassium and Phosphorus containing compound, possibly monopotassium phosphate.

EDS spectrum showing KPO4 and NaCl
Of course, NaCl is seemingly in everything so I poked around and discovered that there are areas of crystals within the crystals and those are the NaCl rich areas. Since my speculation was that the special fluid pouch was salt water, I decided to get a second ‘grow your own tree’ to test the cardboard before adding the fluid. This is when the real fun started.

I opened the new package and put a sample of the cardboard on a stub. It’s always a nice reminder to look at paper and remember that it was once living, when you see the cellular features.

SEM image of cardboard
But the chemistry was not very interesting, except for a few NaCl crystals – so where was the Potassium and Phosphorous coming from? I opened the fluid pouch and dropped a small drop on the cardboard, almost immediately the crystals started growing and I quickly popped it into the SEM vacuum. This was amazing!

In situ crystal growth after 5 minutes
I confirmed that this with a spectrum showing K and P peaks!

Spectrum showing KPO4

Since crystals don’t grow in an SEM (even at the highest pressure I had), I vented and let it grow, but the vac must have “stunted” the tree growth. So I put more fluid on, grew it for an hour and got my best crystal images yet, like seeing snow inside an SEM.

In situ crystal growth after one hourIn situ crystal growth after one hour
I hope you enjoyed sharing in my holiday chemistry science experiment experience. As you will see, chemistry and candy are real important in my life, which sets us up nicely for a future blog post on a tooth with a cavity that I found fascinating!