ADVANCED MATERIALS & PROCESSES | MAY/JUNE 2025 1 7 thresholding in Fig. 5a as well as the dark field image of the selected coinciding diffraction peaks in Fig. 5b. The SAED pattern indicates a coinciding diffraction peak for the (0 3 1)α-Fe and (3 0 3 12)Ti2O3 and for the (0 3 1)α-Fe and (3 0 3 12)Ti2O3 planes respectively, shown in Fig. 5a. The corresponding dark field image in Fig. 5b, when focused on the selected diffraction peak, highlights both the particle boundary phase and the adjacent acicular ferrite confirming the lattice coherency between these two phases. The assumption was furthermore tested with the previously obtained TKD data. Here, PF maps of both the boundary phase and the adjacent acicular ferrite were created and compared to determine the angle difference between both, as shown in Fig. 6. calculations for the rhombohedral Ti2O3 and α-Fe cubic system are shown in the following: With the lattice parameters aTi2O3=0.5149 nm, cTi2O3=1.3642 nm, and aα-Fe=0.2866 nm for Ti2O3 and α-Ferrite respectively the following plane constants were derived: The values coincide well with an error of around 0.0003 nm or 0.3 % at room temperature, which confirms the TEM results. This was then also further extended to higher temperatures using literature values from Kadowaki et al. for Ti2O3 and from Masing et al. for α-Fe[8,9]: with aTi2O3,700°C=0.5125 nm, cTi2O3,700°C=1.39 nm, and aα-Fe,700°C=0.2885 nm Fig. 6 — Pole figure maps of (a) Fe (alpha, ferrite, bcc) and (b) Ti2O3 in the sample obtained by evaluating Fig. 4b. The matching planes can be found in the red circled area. (a) (b) It was found that no angular difference could be determined, hence confirming the assumption. Lastly, the lattice parameters were compared using literature values and crystallographic information. The lattice parameter as approximated lattice constants at a temperature of 700°C. It was therefore found that the lattice parameter was an almost perfect match at a temperature of 700°C, which was the closest possible approximation to the estimated formation temperature with the available data. Notably, the nucleation of acicular ferrite, as a thermodynamically driven process, depends on the cooling rate, which is rapid in electron beam welding and extends the thermal stability of austenite, thereby enabling the formation in this temperature range. Finally, as the material cools from higher temperatures, Ti₂O₃ exhibits anisotropic deformation of the unit cell, in contrast to the isotropic behavior of α-Fe. Therefore, when projecting back from room temperature to 700°C, a slight angular distortion between the boundary phase and the matrix cannot be ruled out. CONCLUSION The procedure presented to evaluate acicular ferrite nucleation was successfully applied to a nucleation site. It was shown that the particle of interest was surrounded by acicular ferrite, with laths nucleating from the particle. Highly localized chemical enrichment was observed within the particle, with the main elements being Al, Ti, Ca, Mg, and O. Furthermore, a boundary phase of Ti2O3 was identified and coherency between this phase and an adjacent acicular ferrite lath was confirmed using TEM, TKD, and lattice calculations. These findings underline the importance of titanium oxides in the formation of acicular ferrite, which is widely discussed in literature. The successful integration of multiple characterization techniques, including light microscopy, electron
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