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Xe Plasma FIB


Figure 4 : Tungsten carbide WC-11 wt.% Co. (a) Reconstructed volume of 150 × 120 × 80 µm 3 , with inset showing zoomed-in details of a facetted WC grain shown for 25 × 25 × 15 μ m 3 sub-volume size. Remaining images show EBSD analysis results: (b) band contrast, (c) phase map (WC red, Co-blue), and (d) Euler-colored orientation map.


material. T e goal of the analysis was to understand the complex 3D microstructure of this material, in particular the size, morphology, and arrangement of the embedded dendrites. T e size of the dendrites in this case was too large for eff ective observation using the limited volumes accessible using a Ga + FIB-SEM. Tungsten carbide . T is material is used in a number of applications where a very hard-wearing surface is required, which includes faces for various cutting tools. T e WC-11 wt% Co sample is very challenging to prepare eff ectively using the Ga + FIB, possibly because of some chemical interaction. T erefore images and EBSD maps were recorded from the PFIB-prepared cross sections of this material to assess the quality of results on what is considered a material that is diffi cult to FIB machine. Human dentine . Lastly a biological sample of human dentine was prepared for examination with a Nanoscale X-ray CT (NanoCT). T is insulating material illustrates a diff erent perspective on the type of work that can be eff ectively carried out with the PFIB. T e time needed to produce a pillar of ~50 μ m diameter and ~100 μ m height would be practically prohibitive in the Ga + FIB. T e bulk sample was gold-coated to alleviate charging. Coarse milling was conducted at 30 kV, and a series of milling currents of decreasing magnitude, from 1300 nA to 180 nA, was employed followed by a fi nal shape-defi ning milling at 59 nA to give a smooth fi nish. A layer of Pt was deposited on top of the pillar to protect it during machining. Platinum was also used to attach the pillar to the Easyliſt TM probe for liſt ing the pillar out of the bulk sample and placing it on the pin sample holder.


Results


Aluminum stress corrosion crack . T e results of the ASNV of the stress corrosion crack in the 7000 series aluminum


2016 May • www.microscopy-today.com


sample are shown in Figure 2 . T e total volume imaged was 100 × 110 × 12 μ m 3 , acquired with a total of 241 slices each 50 nm thick. T e image pixel size was (16 nm) 2 as recorded using the through-the-lens electron detector (TLD). T e total time to collect 1 slice was 3 minutes including 40 s slicing time. Figure 2b shows a magnifi ed region that has been post-processed with an adaptive histogram equalization and median fi lters. T e grains and precipitates are clearly visible. Figure 2c shows a 3D rendering of the precipi- tates in a small volume of the material. T e arrangement of these precipitate particles along the grain boundaries is visible. Many of the smaller intragranular precipitates are visible in the slice images but are typically smaller than the slice thickness of 50 nm, and so they are diffi cult to label separately. T is range of scales (100 µm × 100 μ m cross section and the 18 nm pixel size) allows understanding of the meaningful scales of the stress corrosion crack such that the results here can be linked to light microscopy and microscale X-ray


CT studies going up in scale to the entire crack. Further details of the microstructure could also be obtained by linking to higher- resolution analysis using fi ne-scale SEM or possibly TEM analysis. T e nature of stress corrosion cracks and the interaction they have with the microstructure demands a 3D understanding. Zirconium-based bulk metallic glass . The bulk metallic glass sample is shown in Figure 3 . T e total volume imaged was 120 × 100 × 68 μ m 3 , a total of 678 separate 100 nm thick slices. T e image pixel size was (24 nm) 2 as recorded using the TLD. T e total time to collect 1 slice, including slicing and imaging was 120 s. T e resulting microstructure is a complex array of dendrites that grow out from a central nucleation point, which is diffi cult to understand from a 2D section. As shown in Figures 3 a and 3 b, SST quickly reveals the 3D arrangement of the dendrites within the glass matrix and forms the basis for understanding the microstructure. Again the combination of large volumes (to capture multiple dendrites) with high resolution (to capture the dendrite arms), as well as the strong contrast, necessitates the use of the PFIB-SEM and its capabilities. Tungsten carbide . Figure 4 shows the microstructure of the WC-11 wt% Co specimen. Two volumes were captured: (1) an ASNV volume 100 × 100 × 80 μ m 3 with a total of 800 individual 100 nm thick slices. (2) A 3D EBSD volume 100 × 100 × 3 μ m 3 , capturing a total of 33 slices at 100 nm thick. T e EBSD conditions used were 20 kV and 22 nA, with a step size of 200 nm and a map size of 515 × 530 pixels. T e total time to acquire the data for one slice was about 51 minutes: 51 s slicing time and 50 minutes to collect the EBSD map from each slice.


Figure 4a shows a 3D image of the structure. A large number of grains have been captured making these results statistically signifi cant when trying to understand the size


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