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