What Do You Do? and Whatever is Electron Backscatter Diffraction?

Editor’s note: This blog was written in Chinese by Sophie, describing the challenges of explaining her work for EDAX to her friends and family in China.  Please note that any linguistic clumsiness in the English version is the sole responsibility of the editor (and ‘Google translate’) and has nothing to do with Sophie’s original text!

Dr. Sophie Yan, Applications Engineer China, EDAX

My family, friends and classmates often ask me, “what are you doing now?” – and I usually find it very difficult to give them an answer. Of course, different people need different answers. I once said the full name of EBSD to a bunch of my cousins, and then they looked at each other, completely astonished. They had heard every word clearly, but without the relevant background, they had absolutely no idea what I was talking about. I can explain at greater depth to my classmates and work partners, but even with there, I can sometimes see by the expression on the faces of some of the people that they simply don’t understand me.

Since I have become an EBSD applications engineer, it seems that I often do EBSD education or promotion. I am determined to make my future work easier.

The full name of EBSD is Electron Backscatter Diffraction, and this technique solves the challenges caused by the crystal orientation of the microstructure of materials. In this case, the word crystal refers to long-range orderly arrangement of the atoms making up a crystal material, not something like common glass that has a crystal-clear shape and appearance. In this case, the atoms within the glass are disordered.  Why do we care about the orientation of the crystal? Because the orientation of the crystal is closely related to the performance of the material. As shown in Figure 1 below, each of the two pieces of wood has a different grain orientation. If we want to chop the wood, it will be much easier to chop the piece on the left as we will be going with the grain structure. It will be much more difficult to go against the grain and chop the piece on the right. In other words, we try to ensure that the materials we use are always as strong as the piece of wood on the right, and hence much more durable…

Figure 1. Wood with different textures

The professional term used to describe this molecular arrangement within a material is anisotropy. From a literal point of view, it can be understood that the performance of materials in different directions is different. This is a macroscopic performance. From the perspective of microstructure, it is due to the different orientation distribution of small structural units (here, crystal grains) of the material. If it is randomly distributed, it is isotropic, as shown in the left figure below. If it is not randomly distributed, but with a certain aspect of preference, as shown in the right picture, it is anisotropic. Another concept of texture, which refers to the distribution of orientation, can also be introduced here. Texture is closely related to the material properties. In fact, EBSD was invented and developed by a group of material scientists who were studying the texture of materials. At the international texture conference (ICOTOM), which is held every three years, various aspects of EBSD now provide about one-third of the total content.

Figure 2. Random distribution of orientation; preferred distribution of orientation

There are many tools available for measuring texture, such as X-ray diffraction, electron diffraction, neutron diffraction, EBSD. XRD measurement is convenient for a wide range of applications, but XRD is a statistical macroscopic orientation that does not give the orientation of each grain as shown in Figure 2. With neutron diffraction, you have to consider the cost and where to do it… so EBSD is popular. In the past two years, there has been an explosive growth in the study and use of EBSD in China. It seems that everyone is finally realizing that this analysis technique is less expensive, analysts can achieve excellent results, and these results are available more and more quickly.

To say that the results are good, in fact, refers to the diversity of EBSD data analysis results. The first-hand data collected by EBSD is the orientation information of each point of the material. Through the processing of this first-hand data by special analysis software, the orientation distribution-texture information can be obtained, and the people who care about the material properties, especially the preferred orientation, get the information they need.

Measurement points of similar orientations can be grouped together as grains if these points neighbor each other. Therefore, grain related information such as grain size and grain shape can be obtained. The orientation relationship between 2 neighboring grains can be described as a grain boundary. These boundaries can be colored by various properties such as misorientation, CSL, or phase. EBSD can also measure the effects of strain in a material, as this strain causes small changes of orientation within a grain that can be detected and mapped to show the deformed microstructure. Through these graphs, we can optimize the process parameters, failure analysis, and cooperate with various sample stations to perform in-situ tensile analysis. In-situ heating analysis, combined with other means to identify the phase.

Finally, a beautiful orientation map is created: this is the most common EBSD result for everyone, that is, the orientation map represented by different colors. The daily work of engineering students is often boring, but we also have such beautiful colors!

Figure 3. IPF surface map

Vacationing Between a Rock and a Hard Place?

Shawn Wallace, Applications Engineer, EDAX.

One of the perks of both my degree (Geology) and my current job is that I have travelled extensively. In all those travels, I had been to 47 of the 48 contiguous US States, with Maine being the missing one. This year, I decided to be selfish and dragged the family to Maine on vacation, so I that could tick off the final one.

Being a member of the Wallace family means vacation is a time for strenuous hikes and beating on rocks to unlock their inner goodies, to add to our ever growing rock and mineral collection. This vacation was no different. Maine is home to some of the best studied and known Pegmatites, and they quickly became our goal. Pegmatites are neat for a several reasons, the main two being that they tend to form giant crystals (a 19 foot long Beryl found in Maine) and weird minerals in general tend to form in them.

I was able to track down some publicly accessible sites, found a lovely home base to rent for the week, and we set off for a week long rockhounding adventure. Ok not all week. We took a couple days off to go swimming, as it got up over 90F (>32C).

Figure 1. Dendrites cover this massive feldspar sample on nearly all faces.

Our first stops yielded the usual kind of rocks I was expecting, but another site did not. There we found dendrites everywhere. The rock itself is a massive feldspar (Fig. 1). You can see that most of the dendrites nucleate at the edge of a fracture surface and then do their fractal thing on the surface itself. Wanting to better understand the sample, I started searching for previous EBSD work on geological dendrites. While a lot exists in the metals world, very little exists in the geological world. To me, this means I have work to do. Let’s see what I can do to get some useful data on this sample!

P.S. I have Alaska and Hawaii to go. Who needs an onsite training in those states? 😉

Countdown to M&M…..

Patrick Camus, PhD, Director of Engineering, EDAX

This time of year is, at least in the US, preparation time for the Microscopy and Microanalysis (M&M) meeting. Like most big shows, every attendee has a significant amount of preparation to perform in the weeks (days?) leading up to their travel date. Most readers of this blog will be platform or poster presenters. You may be under stress to collect that last set of experimental data to fill that last hole in the analysis to finalize your presentation.

Life is not so different for the commercial exhibitors like EDAX. Unknown to the general participants, there are many departments under similar pressures to ensure a productive meeting for all attendees. Engineering is applying the finishing touches to new products. Software Engineering is approving the latest versions of software for release. Marketing Communications is contacting current and prospective customers to attend equipment demos and workshops during the exhibition hours. Marketing is receiving the final graphics of product literature for decorating the booth. Service is scheduling engineers to install all the EDAX microanalysis systems in our booth and those of our electron microscope associates. Applications scientists are finalizing their presentations for the meeting but also for the demos and EDAX workshops to be performed in our booth. Logistics is coordinating the hotels for our employees and shipping our equipment both to and from the venue. About the only employees not under stress before the meeting are Sales who coast now but are under the most stress (or is it strain) during the week of the show.

The exhibitors may seem very relaxed to the visitors during the show, but that image derives from the total effort that they are putting forth now so that you have the best experience possible.

We look forward to seeing all of you in Baltimore, or your next show!

Click here for more information about EDAX at this year’s event.

Crown Caps = Fresh Beer?

Dr. Felix Reinauer, Applications Specialist Europe, EDAX

A few days ago, I visited the Schlossgrabenfest in Darmstadt, the biggest downtown music festival in Hessen and even one of the biggest in Germany. Over one hundred bands and 12 DJs played all kinds of different music like Pop, Rock, Independent or House on six stages. This year the weather was perfect on all four days and a lot of people, celebrated a party together with well known, famous and unknown artists. A really remarkable fact is the free entrance. The only official fee is the annual plastic cup, which must be purchased once and is then used for any beverage you can buy in the festival area.

During the festival my friend and I listened to the music and enjoyed the good food and drinks sold at different booths in the festival grounds. In this laid-back atmosphere we started discussing the taste of the different kinds of beer available at the festival and throughout Germany. Beer from one brewery always tastes the same but you can really tell the difference if you try beer from different breweries. In Germany, there are about 1500 breweries offering more than 5000 different types of beer. This means it would take 13.5 years if you intended to taste a different beer every single day. Generally, breweries and markets must guarantee that the taste of a beer is consistent and that it stays fresh for a certain time.

In the Middle Ages a lot of people brewed their own beer and got sick due to bad ingredients. In 1516 the history of German beer started with the “Reinheitsgebot”, a regulation about the purity of beer. It says that only three ingredients, malt, water, and hops, may be used to make beer. This regulation must still be applied in German breweries. At first this sounds very unspectacular and boring, but over the years the process was refined to a great extent. Depending on the grade of barley roasting, the quantity of hops and the brewing temperature, a great variety of tastes can be achieved. In the early times the beer had to be drunk immediately or cooled in cold cellars with ice. To take beer with you some special container was invented to keep it drinkable for a few hours. Today beer is usually sold in recyclable glass bottles with a very tight cap keeping it fresh for months without cooling. This cap protects the beer from oxidation or getting sour.

Coming back to our visit to the Schlossgrabenfest; in the course of our discussions about the taste of different kind of beer we wondered how the breweries guarantee that the taste of the beer will not be influenced by storage and transport. The main problem is to seal the bottles gas-tight. We were wondered about the material the caps on the bottles are made of and whether they are as different as the breweries and maybe even special to a certain brewery.

I bought five bottles of beers from breweries located in the north, south, west, and east of Germany and one close to the EDAX office in Darmstadt. After opening the bottles, a cross section of the caps was investigated by EDS and EBSD. To do so, the caps were cut in the middle, embedded in a conductive resin and polished (thanks to René). The area of interest was the round area coming from the flat surface. The EDS maps were collected so that the outer side of the cap was always on the left side and the inner one on the right side of the image. The EBSD scans were made from the inner Fe metal sheet.

Let´s get back to our discussion about the differences between the caps from different breweries. The EDS spectra show that all of them are made from Fe with traces of Mn < 0.5 wt% and Cr, Ni at the detection limit. The first obvious difference is the number of pores. The cap from the east only contains a few, the cap from north the most and the cap from the middle big ones, which are also located on the surface of the metal sheet. The EBSD maps were collected from the centers of the caps and were indexed as ferrite. The grains of the cap from the middle are a little bit smaller and with a larger size distribution (10 to 100 microns) than the others, which are all about 100 microns. A remarkable misorientation is visible in some of the grains in the cap from the north.

Now let´s have a look at the differences on the inside and outside of the caps. EDS element maps show carbon and oxygen containing layers on both sides of all the caps, probably for polymer coatings. Underneath, the cap from the east is coated with thin layers of Cr with different thicknesses on each side. On the inside a silicone-based sealing compound and on the outside a varnish containing Ti can also be detected. The cap from the south has protective coatings of Sn on both sides and a silicon sealing layer can also be found on the inside. The composition of the cap from the west is similar to the cap from the east but with the Cr layer only on the outside. The large pores in the cap from the middle are an interesting difference. Within the Fe metal sheet, these pores are empty, but on both sides, they are filled with silicon-oxide. It seems that this silicon oxide filling is related to the production process, because the pores are covered with the Sn containing protective layers. The cap from the north only contains a Cr layer on the inside. The varnish contains Ti and S.

In summary, we didn’t expect the caps would have these significant differences. Obviously, the differences on the outside are probably due to the different varnishes used for the individual labels from each of the breweries. However, we didn’t think that the composition and microstructure of the caps themselves would differ significantly from each other. This study is far from being complete and cannot be used as a basis for reliable conclusions. However, we had a lot of fun before and during this investigation and are now sure that the glass bottles can be sealed to keep beer fresh and guarantee a great variety of tastes.

Building an EBSD Sample

Matt Nowell, EBSD Product Manager, EDAX

Father’s Day is this weekend, and I like to think my kids enjoy having a material scientist for a father. They have a go-to resource for math questions, science projects are full of fun and significant digits, and when they visit the office they get to look at bugs and Velcro with the SEM. I’m always up to take them to museums to see crystals and airplanes and other interesting things as we travel around. That’s one way we have tried to make learning interactive and engaging. Another activity we have recently tried is 3D printing. This has allowed us to find or create 3D digital models of things and then print them out at home. Here are some fun examples of our creations.
At home we are printing with plastics, but in the Material Science world there is a lot of interest and development in printing with metals as well. This 3D printing, or additive manufacturing, is rapidly developing as a new manufacturing approach for both prototyping and production in a range of industries including aerospace and medical implants. Instead of melting plastics with a heated nozzle, metal powders are melted together with lasers or electron beams to create these 3D shapes that cannot be easily fabricated by traditional approaches.

In these applications, it is important to have reliable and consistent properties and performance. To achieve this, the microstructure of the metals must be both characterized and understood. EBSD is an excellent tool for this requirement.

The microstructures that develop during 3D printing are very interesting. Here is an example from a Ni-based superalloy created using Selective Laser Melting (SLM). This image shows a combined Image Quality and Orientation (IQ + IPF) Map, with the orientations displayed relative to the sample normal direction. Rather than equiaxed grains with easily identifiable twin boundaries, as are common with many nickel superalloys, this image shows grains that are growing vertically in the structure. This helps indicate the direction of heat flow during the manufacturing process. Understanding the local conditions during melting and solidification helps determine the final grain structure.
In some materials, this heating and cooling will cause not only melting, but also phase transformations that also affect the microstructure. Ti-6Al-4V (or Ti64) is one of the most common Titanium alloys used in both aerospace and biomedical applications, and there has been a lot of work done developing additive manufacturing methods for this alloy. Here is an IQ + IPF map from a Ti64 alloy built for a medical implant device.
At high temperatures, this alloy transforms into a Body-Centered Cubic (or BCC) structure called the Beta phase. As the metal cools, it transforms into a Hexagonal Closed Pack (HCP) structure, called the Alpha phase. This HCP microstructure develops as packets of similarly oriented laths as seen above. However, not all the Beta phase transforms. Here is an IQ + Phase EBSD map, where the Alpha phase is red and the Beta phase is blue. Small grains of the Beta phase are retained from the higher temperature structure.
If we show the orientations of the Beta grains only, we see how the packets relate to the original Beta grains that were present at high temperatures.
The rate of cooling will also influence the final microstructure. In this example, pieces of Ti64 were heated and held above the Beta transition temperature. One sample was then cooled in air, and another was quenched in water. The resulting microstructures are shown below. The first is the air-cooled sample.
The second is the water-cooled sample.

Clearly there is a significant difference in the resulting structure based on the cooling rate alone. As I imagine the complex shapes built with additive manufacturing, understanding both the local heating and cooling conditions will be important for optimization of both the structure and the properties.

A Little Background on Backgrounds

Dr. Stuart Wright, Senior Scientist EBSD, EDAX

If you have attended an EDAX EBSD training course, you have seen the following slide in the Pattern Indexing lecture. This slide attempts to explain how to collect a background pattern before performing an OIM scan. The slide recommends that the background come from an area containing at least 25 grains.

Those of you who have performed re-indexing of a scan with saved patterns in OIM Analysis 8.1 may have noticed that there is a background pattern for the scan data (as well as one of the partitions). This can be useful if re-indexing a scan where the raw patterns were saved as opposed to background corrected patterns. This background pattern is formed by averaging 500 patterns randomly selected from the saved patterns. 500 is a lot more than the minimum of 25 recommended in the slide from the training lecture.

Recently, I was thinking about these two numbers – is 25 really enough, is 500 overkill? With some of the new tools (Callahan, P.G. and De Graef, M., 2013. Dynamical electron backscatter diffraction patterns. Part I: Pattern simulations. Microscopy and Microanalysis, 19(5), pp.1255-1265.) available for simulating EBSD patterns I realized this might be provide a controlled way to perhaps refine the number of orientations that need to be sampled for a good background. To this end, I created a set of simulated patterns for nickel randomly sampled from orientation space. The set contained 6,656 patterns. If you average all these patterns together you get the pattern at left in the following row of three patterns. The average patterns for 500 and 25 random patterns are also shown. The average pattern for 25 random orientations is not as smooth as I would have assumed but the one with 500 looks quite good.

I decided to take it a bit further and using the average pattern for all 6,656 patterns as a reference I compared the difference (simple intensity differences) between average patterns from n orientations vs. the reference. This gave me the following curve:
From this curve, my intuitive estimate that 25 grains is enough for a good background appears be a bit optimistic., but 500 looks good. There are a few caveats to this, the examples I am showing here are at 480 x 480 pixels which is much more than would be used for typical EBSD scans. In addition, the simulated patterns I used are sharper and have better signal-to-noise ratios than we are able to achieve in experimental patterns at typical exposure times. These effects are likely to lead to more smoothing.

I recently saw Shawn Bradley who is one of the tallest players to have played in the NBA, he is 7’6” (229cm) tall. I recognized him because he was surrounded by a crowd of kids – you can imagine that he really stood out! This reminded me that these results assume a uniform grain size. If you have 499 tiny grains encircling one giant grain, then the background from these 500 grains will not work as a background as it would be dominated by the Shawn Bradley grain!

One Analysis Technique – So Many Options!

Roger Kerstin, North America Sales Manager, EDAX

X-ray Fluorescence (XRF) solutions – which type of XRF instrument should I choose?

Most of the XRF systems out there are very versatile and can be used in many different applications, but they are typically suited for a specific type of analysis. Since the discovery of XRF many decades ago there have been new developments and new instruments just about every year. The term Florescence is applied to phenomena in which the absorption of radiation of a specific energy results in the re-emission of radiation of a different energy. There are two different types of detectors for XRF systems: Wavelength Dispersive (WDS) and Energy Dispersive (EDS).

In energy dispersive analysis, the fluorescent X-rays emitted by the material sample are directed into a solid-state detector which produces a “continuous” distribution of pulses, the voltages of which are proportional to the incoming photon energies. This signal is processed by a multichannel analyzer (MCA) which produces an accumulating energy spectrum that can be processed to obtain analytical data.

In wavelength dispersive analysis, the fluorescent X-rays emitted by the material sample are directed into a diffraction grating monochromator. The diffraction grating used is usually a single crystal. By varying the angle of incidence and take-off on the crystal, a single X-ray wavelength can be selected. The wavelength, and therefore the energy, obtained is given by Bragg’s law:

nλ = 2d Sinθ

In the XRF world there are many different types of instruments to choose from: large systems to small systems; high powered systems to low powered systems, floor standing systems to benchtop to portable systems.

What do I choose, where do I start?

The answer to these questions is that it really depends on the samples you are trying to measure and the performance you are trying to achieve. I really classify these instruments in 3 different categories: bulk, portable, and small spot.

Bulk XRF: This typically means that you have samples that are either powders, liquids or even solids that you need to analyze quickly. Bulk instruments have a large x-ray spot size to excite a lot of the elements fast and get a quick answer. They can be EDS or WDS instruments, benchtop or floor standing, and low or high power. The kind of analyzer will determine what you can or cannot measure. The higher the power, the lighter the elements and the lower the concentrations. The benchtops typically are lower power (50kv and lower) and are usually decent for go/no go type analysis and even everyday type of analysis when super low LOD’s are not needed, or light elements (below Na) are not of a concern. If you need lighter elements or lower LOD’s then typically you would go with a high power WDS system and these typically can go up to 4kw of power and have a vacuum chamber or He environment .

Portable XRF: This is just what is says – portable. These analyzers are typically used for sorting metals, in the geological field, or anything that you can’t just bring to the lab. The performance of these have come a long way and they are a critical tool for many industries. They tend to have a larger spot size but since they are portable they must be light to carry around all day. They are typically lower power and lower current, which does not allow them to have the same type of performance as the lab type instruments but usually they are good for sorting and identifying samples. They are also very good for ancient artifacts or paintings that can’t be brought to a lab.

μXRF (Micro spot XRF): These are the instruments that have a small spot size compared to all other XRF systems and they are used in smaller sample identification or mapping of a sample. There are several different types of μXRF analyzers. Some use collimators to focus the beam (this typically loses intensity) for applications like coating thickness testing or alloy id. These are usually designed to be inexpensive and benchtop for quality control applications. They are versatile but also limited to the elements they can measure. Most of these only analyze down to Potassium as they usually do the analysis in an air environment. Then there are μXRF systems that use optics to focus the x-ray to smaller spot sizes. These are used for more in-depth analysis, and are equipped with a vacuum chamber, mapping and low LODs.

Before buying an XRF system many factors must be taken into consideration and you need to ask yourself some of the following questions to really determine the best fit for your applications.

• How big is my sample?
• Can I destroy my sample?
• What levels of detection do I need to measure?
• How many samples per day will I measure?
• Can I pull a vacuum with my sample?
• What elements do I need to measure?
• What type of flexibility do I need for multiple sample types?
• What size features or samples do I need to measure?
• How much money do I have?

As you can see there are many questions to answer and many options for XRF instruments. The more you know about what you want to measure, the better you can narrow down your search for the proper instrument.

XRF is a very powerful technique but you do need to get the proper tool for the job.
Happy hunting and good luck!