Month: December 2015

“What do we do?” – A Newcomer’s Perspective.

Shawn Wallace – Applications Engineer EDAX

As the new guy, I get to see everything in the office here in Mahwah for the first time. The thing that has impressed me the most is both the breadth of the material we cover and the depth in which we can do so. I have had the pleasure of diving in to cabinets and desiccators to look over literally decades of samples. Through that learning experience, I have needed to think about why these specimens are run here and just how important our job is in helping others understand what they have and how we can help them and their products be better by figuring out what their product really is.

One of the first samples that really stood out to me, mainly because of its size, is a brake pad.

Figure 1. Your everyday brake pad.

Figure 1. Your everyday brake pad.

Why would people want us to look at a brake pad? I had no idea until I started to think what properties a consumer would want in a brake pad. You want it to be able to withstand both high amounts of wear and high temperatures. Not many materials can do that by themselves and still be cheap enough for the average person to not really think about the cost. You can see just by looking at the picture that the brake pad is made of many phases. You need to understand where each phase is, how it is oriented, and how it changes with wear and tear. That is where the EDAX Applications lab comes in. Our products help the customer understand what they have and where it is.

While the brake pad stood out mainly for its sheer size, something much smaller caught my eye, a little pinkish square that turned out to be a pill.

Figure 2. A random pinkish pill on an SEM stub.

Figure 2. A random pinkish pill on an SEM stub.

I had another detective story to think about. As a geologist by training, I was out of my league, and while I had some ideas of why we would look at pharmaceuticals, I did what every good scientists does when they are not sure, search the literature. Ok, I really just googled it. What I found out made sense and our part in the process of quality control clicked. Think about what a pill is. It is mostly filler and some active ingredient. Both have their roles and how these two ingredients are physically related to each other matters. You need to know if the active ingredient is dispersed throughout the sample or maybe coated in another ingredient. All these matter on how long the pill lasts in your system. Also, you want to make sure that nothing out of the ordinary is in your product, and our products can do all this quickly, helping a company delivery a quality product, with us doing our part.

Finally, I found the newest sample in our lab, a nice piece of shell from a sea critter. I knew exactly why it was there and what it was there for as I had brought it in to help an old friend. It was a piece of a Nautilus shell, the amazing looking cephalopod. My job is to understand how the shell grows, how that growth relates to its life cycle, and how the shell can withstand extreme depths that this creature can do go. All these questions can be answered by looking at how the chemistry of the shell changes, how the grains are oriented, and how the grains interact with each other.

Figure 3. Piece of a Nautilus shell.

Figure 3. Piece of a Nautilus shell.

So many interesting questions to answer. So many interesting tools to help answer those questions. I think I am going to like it here.

Old Dogs and New Tricks!

Matt Nowell, Product Manager EBSD, EDAX

This year, three of us in the EBSD development group (Stuart Wright, Scott Lindeman, and myself) celebrated 20 years at EDAX.  I consider myself quite fortunate to have gotten involved with EBSD so early in its commercial development, and it’s been exciting and rewarding to see its growth, both in terms of number of users but also in the wide array of applications.

However, there are still some characterization challenges that we continue to revisit.  One example is differentiating ferrite from martensite in different steel alloys.  This phase differentiation application is challenging because martensite is crystallographically only slightly distorted from the ferrite body-centered cubic cell, and that distortion will depend on carbon content and thermal processing history.  This makes it difficult to differentiate these phases directly via crystallographic structure measurements.  Because the martensitic phase is generally more strained, most differentiation work has focused on using the EBSD Image Quality value as the key differentiation metric [1-2].

Figure 1.

Figure 1.

As new features are developed, it is enjoyable to see where these features can be applied, and what benefits might be gained from them beyond what was initially envisioned.  One example is Neighbor Pattern Averaging and Reindexing or NPAR.  NPAR improves the signal to noise of an EBSD pattern by averaging each pattern with all the neighboring patterns, as shown in Figure 1.    NPAR was initially created as a method of successfully indexing some very noisy patterns we received from a customer, but we quickly found benefits trying this approach on a range of different materials and under different SEM operating conditions.  More details can be found in an earlier blog post at : https://edaxblog.com/2015/09/.

Figure 2a. Figure 2b.

Figure 2 shows EBSD Image Quality (IQ) maps collected on a dual phase ferritic-martensitic steel sample.  Fig 2a shows the IQ map collected under standard conditions, while Fig 2b shows the IQ map after NPAR processing.  It can easily be seen that the phase contrast has been increased after using NPAR.  This is because the quality of the EBSD pattern from the martensitic phase is lower due to the internal strain and not because of camera parameters.  This means that the spatial pattern averaging of NPAR does not improve the IQ values for the martensitic phase at the same rate as it does for the ferritic phase, hence increasing the phase contrast values.

Figure 3a. Figure 3b.

NPAR processing does have another effect that can be observed.  Using NPAR, orientation precision is improved through better Signal to Noise levels in the EBSD pattern, resulting in more precise band detection. Because of this effect, the average misorientation (as measured here with the Kernel Average Misorientation metric) measured within each martensitic grain is lower with NPAR processing.  The results with and without NPAR processing are shown in Figure 3.  While NPAR does improve indexing and orientation precision performance, this improvement reduces the effectiveness of the KAM value to differentiate these phases.  I think the fact that NPAR improves one indirect differentiation method while not improving another shows why this is a challenging characterization problem.

In the end, while NPAR does offer some improvements, we still have not found a fully satisfactory solution to the ferrite-martensite differentiation problem.  I look forward to continuing to work on this and other characterization problems as we continue with EBSD product development.

[1] Wilson, A. W., J. D. Madison and G. Spanos (2001). “Determining phase volume fraction in steels by electron backscattered diffraction.” Scripta Materialia 45(12): 1335-1340.
[2] Nowell, M. M., S. I. Wright and J. O. Carpenter (2009). A Practical investigation into Identifying and Differentiating Phases in Steel Using Electron Backscatter Diffraction. Materials Processing and Texture. A. D. Rollett. Hoboken, NJ, John Wiley & Sons: 285-292.

To learn more about NPAR click here to see our video overview.