Matt Nowell – Product Manager EBSD, EDAX
I’ve been at EDAX, and formerly TSL, for 20 years now, and given that OIM makes such beautiful images, one of the more ironic facts about my career is that I am color blind. That can sometimes make interpreting colored microstructural images a bit more challenging, and I’m very grateful for the flexibility in coloring within OIM Analysis that the software guys have put in for me (although I think they keep the default first 2 colors in phase maps red and green just because I won the last golf Burrito Open).
Occasionally, however, it’s very easy to read the microstructure. Take this image for example:
This image is an Inverse Pole Figure (IPF) map showing the crystallographic orientation. While I’m sure if one were properly motivated, you might find the right vector in sample space to turn this IPF map into a test for colorblindness, even I can see that it spells out DOE. This very cool example was created by researchers at Oak Ridge National Laboratory, where they used an additive manufacturing process called Electron Beam Melting (EBM) to spatially modify the solidification texture development in a nickel-based superalloy. One can easily imagine that if you can control the local microstructure, you can then design and engineer the microstructure to optimize properties spatially for specific loads and applications. You can learn more about the work at Oak Ridge at: http://3dprint.com/19477/ebm-printing-3d-ornl/ or http://web.ornl.gov/sci/manufacturing/research/additive/.
Other approaches have also been used to write into the microstructure, which I guess is the equivalent to changing the font and font size.
In this example from the Else Kooi Laboratory, formerly known as the Dimes Technology Center, at the Delft University of Technology (http://www.dimes.tudelft.nl/EKL/Home.php) a laser beam was used to locally induce recrystallization in polycrystalline silicon. This approach has been used to develop thin film transistors used in things like liquid crystal displays. The writing is visible in both the OIM image quality (IQ) map(top) and the grain map (bottom), where adjacent measurement pixels of similar orientations are grouped together as grains, and then these resolved grains are randomly colored to show size and morphology. That approach gives each letter a different color.
OIM has even been used to read the deformation in metals to recover destroyed serial numbers in metal objects like firearms. In the images below, an “X” has been stamped into a piece of stainless steel (a), and then polished to visually remove the marker (b).
Researchers at NIST have then used OIM to map over the area, with the corresponding IQ map shown here:
The residual plastic deformation present in the microstructure causes a lower EBSD IQ value which is used to image the stamped X. Years ago EDAX was featured on the TV show CSI for our Orbis µXRF product. With this forensic application, we are finally ready for a sequel. More information about this application can be found in a paper by Ryan White and Bob Keller in Forensic Science International (R.M. White and R.R Keller, Restoration of firearm serial numbers with electron backscatter diffraction (EBSD) Forensic Science International 249 (2014) pp 266-270) and at http://www.nist.gov/mml/acmd/ebsd-021115.cfm.
While all of these examples have used OIM to visualize the text within the microstructure, my first introduction to this literary metallurgical engineering was observable by eye:
This sample was created for the International Conference on Grain Growth (ICGG), held back in 1995. In keeping with theme of this conference, the characters were placed by locally inhibiting the grain growth while the bulk material was recrystallized.
So, while these pictures many not be worth a thousand words, they do contain at least a thousand grains. The fact that a few words have been engineered into the microstructure by various means is pretty incredible.
Many thanks to Ryan Dehoff at Oak Ridge National Lab, Ryan White and Bob Keller at NIST, and David Field at Washington State University for allowing the use of their images for this blog.