ADVANCED MATERIALS & PROCESSES | MAY/JUNE 2025 16 The particle exhibits a highly intricate internal structure, as revealed by the BSE image. Up to three visible contrasts can be discerned: one shade of lighter color, one more faded dark shade, mostly in the upper middle part of the particle, and the remaining dark shade. These contrasts can be directly attributed to the chemical composition. The EDS maps further confirm this, showing localized chemical enrichment of elements. Overall, the particle can be described as an oxide, with the main elements being Al, Ti, Ca, and Mg. Trace amounts of S, Si, and Mn were also indicated. Mg and Ca particularly seemed to accumulate in areas exclusive to each other, with a less pronounced tendency for Al- and Tirich areas. The faded dark shade in the BSE image can be probably attributed to the absence of Mg in combination with higher Al concentration, while the areas with darker shade contain both Mg and Al. In contrast to this, Ti- and Ca-rich areas are generally of lighter color. With this information, a direction for the TEM lamella along the longest lath axis originating at the particle was chosen, corresponding to the almost horizontal laths in Fig. 2. After sufficient thinning STEM and TKD analysis were performed. The results are shown in Fig. 4. The BSE image in Fig. 3 and the STEM image in Fig. 4a, which shows the perpendicular direction, both reveal an intricate internal structure. These contrasts were then also linked with the TKD evaluations in Fig. 4b. Here it was observed that the particle consisted mostly of amorphous regions, cubic phases, and a rhombohedral boundary phase. This rhombohedral phase has a remarkable light shade in the STEM image and almost blends in with the surrounding matrix. However, it is clearly visible in the indexed TKD image in a pink color in the top left corner of the particle. A good fit (fit value < 0.9, see EDAX OIM 8 documentation) for this phase was obtained for Ti2O3, also nominally known as Tistarite in nature, which also corresponded well with the already observed EDS-measurements on the particle’s general chemical composition. With this knowledge, TEM analysis was performed to uncover direct phase coherency. The results are shown in Fig. 5. Figure 5 showcases the labeled SAED pattern of the boundary phase and the adjacent steel matrix after Fig. 3 — Zoomed-in BSE image accompanied by EDS maps of the particle highlighted in Fig. 2. The particle can be categorized as an oxide, with its main cations being Al, Ti, Ca, and Mg. Local enrichment of Ca/Mg and Al/Ti is observed. Fig. 4 — (a) STEM image of the sliced particle contained within a TEM lamella and (b) filtered TKD image. Regions with α-Fe indications in the TKD measurement were filtered out for easier visualization of the particle. Several cubic phases and amorphous areas are visible within the particle, with this study primarily focusing on the boundary phase in the top le corner (highlighted with a black square, pink color in TKD). (a) (b) Fig. 5 — (a) Indexed SAED pattern, and (b) dark field image of the Ti2O3 boundary phase and adjacent α-Ferrite. The obtained di raction peaks from the SAED pattern a er thresholding have been labeled according to evaluations using the program SingleCrystal. The coinciding di raction peaks at (3 0 3 12)Ti 2O3 and (0 3 1)α-Fe of both phases were selected and shown in the dark field image on the right, highlighting both participating phases and therefore confirming phase coherency. (a) (b)
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