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Complete Characterization with Integrated EDS – EBSD

Introduction

Integrated Energy Dispersive Spectroscopy (EDS) – Electron Backscatter Diffraction (EBSD) systems, also known as EDAX Pegasus Analysis Systems, enable users to easily and efficiently obtain a complete characterization of their samples. EDS provides information on the sample’s elemental composition in an integrated system, while EBSD gives information on the crystallographic structure and orientation. With the APEX Software, a common user interface makes learning and operating the software consistent. EDS and EBSD data can be collected simultaneously at the push of a button. Samples need to be prepared and positioned for EBSD analysis. The EDS and EBSD detectors must be configured on the SEM to both point towards the sample in this position, which is the default geometry for Pegasus Systems. With simultaneous collection, the EDS and EBSD data originate from the same location during mapping for optimal correlation of the two signals. This article will show some information obtained with integrated EDS-EBSD data for complete characterization.

Results and Discussion

Simultaneous EDS-EBSD data was collected from a nickel alloy brazed with a High Entropy Alloy (HEA) filler using an Octane Elite Plus EDS Detector and a Velocity Super EBSD Detector. The sample was kindly provided by Benjamin Schneiderman and Professor Zhenzhen Yu of the Colorado School of Mines. Figure 1 shows an EBSD map with the Image Quality (IQ) measurement displayed as a grayscale image combined with the Inverse Pole Figure (IPF) orientation map (relative to the surface normal direction) displayed in color. Additionally, twin boundaries within the material are shown with white lines. Both the nickel alloy and HEA filler are face-centered cubic.

An EBSD map with the IQ measurement displayed as a grayscale image combined with the IPF orientation map (relative to the surface normal direction) displayed in color.
Figure 1. An EBSD map with the IQ measurement displayed as a grayscale image combined with the IPF orientation map (relative to the surface normal direction) displayed in color.

 

This image shows the braze line horizontally in the middle of the image, with the nickel alloy at the top and bottom of the field of view. The nickel alloy has a significantly larger grain size with a high fraction of twin boundaries, while the HEA filler has smaller grains with minimal twins. There is also a transition region of smaller grain with twins at the Ni-HEA interface. This information is what is typically available with EBSD analysis.

a) An EDS elemental map from nickel collected simultaneously with the EBSD data, with a single-color intensity showing the number of EDS counts per pixel. b) A black-to-thermal coloring scheme is used, highlighting three regions of nickel concentration: a higher region in the nickel alloy, a lower region in the HEA filler, and a depletion region in the center of the braze.
Figure 2. a) An EDS elemental map from nickel collected simultaneously with the EBSD data, with a single-color intensity showing the number of EDS counts per pixel. b) A black-to-thermal coloring scheme is used, highlighting three regions of nickel concentration: a higher region in the nickel alloy, a lower region in the HEA filler, and a depletion region in the center of the braze.

 

Figure 2a shows an EDS elemental map from nickel collected simultaneously with the EBSD data, with a single-color intensity showing the number of EDS counts per pixel. This image shows the reduced concentration of nickel within the HEA braze material. Different coloring schemes can highlight these concentration gradients, as shown in Figure 2b. Here a black-to-thermal coloring scheme is used, highlighting three regions of nickel concentration: a higher region in the nickel alloy, a lower region in the HEA filler, and a depletion region in the center of the braze. Multiple EDS elemental maps can also be combined into a single image, as shown in Figure 3. In the RGB image, the red channel shows the nickel intensity, the green channel shows the oxygen intensity, and the blue channel shows the cobalt intensity. This image shows that the HEA filler has a higher cobalt concentration, with regions of higher oxygen corresponding to the regions of less nickel. This information is typically available with EDS analysis.

A combined RGB image. The red channel shows the nickel intensity, the green channel shows the oxygen intensity, and the blue channel shows the cobalt intensity.
Figure 3. A combined RGB image. The red channel shows the nickel intensity, the green channel shows the oxygen intensity, and the blue channel shows the cobalt intensity.

 

Some of the synergetic advantages of integrated EDS-EBSD analysis are shown in Figure 4. The EDS RGB coloring is the same as in Figure 3. Still, the grain boundary information obtained from simultaneous EBSD data is also shown, with twin boundaries displayed as white lines and random high-angle grain boundaries displayed as black lines. This information allows for direct correlation and analysis of the chemical and crystallographic components of the microstructure. This example shows that some grains at the Ni-HEA interface have a compositional gradient. This combined EDS-EBSD data allows for a better understanding of the diffusion, grain nucleation and growth, and twinning mechanisms that may be active during the brazing process.

This combined RGB map shows the same EDS coloring as Figure 3, with added grain boundary data from simultaneous EBSD collection.
Figure 4. This combined RGB map shows the same EDS coloring as Figure 3, with added grain boundary data from simultaneous EBSD collection.

 

An IQ map at a higher magnification within the center of the braze region.
Figure 5. An IQ map at a higher magnification within the center of the braze region.

 

Pegasus Systems also include advanced tools to take integrated EDS-EBSD analysis to the next level. Figure 5 shows an IQ map at a higher magnification within the center of the braze region. This image shows multiple small precipitates within the microstructure. The EBSD information shows that most precipitates are located along grain boundaries, but a smaller fraction of precipitates are located within grains. Integrated EDS-EBSD information is used to determine a grain-averaged EDS concentration to better identify and characterize these precipitates. This approach significantly reduces the noise within the EDS data. The information can then be used for ChI-Scan™ analysis, where averaged EDS information is used to differentiate crystallographically similar phases. The resultant phase map is shown in Figure 6. With this analysis, each precipitate is fully characterized for composition and crystallography, and this information can be used to better understand how the different precipitate types developed during brazing.

A phase map was created using ChI-Scan analysis.
Figure 6. A phase map was created using ChI-Scan analysis.

 

Conclusion

Integrated EDS-EBSD analysis is a powerful tool to characterize microstructures completely and is readily available through the APEX Software for fast and easy materials analysis.