Impact of Excess Vacancies on Antiphase Domain Growth in Laser Irradiated and Single Crystal Like Fe₃Al Fabricated by Laser Powder Bed Fusion

Fe₃Al intermetallic single crystals show superelasticity due to the interaction between antiphase domain boundaries (APBs) and dislocations [1,2]. Optimizing heat treatment conditions to regulate antiphase domain (APD) structure is important to enhance the superelasticity of Fe₃Al. Previous study derived accurate ordering mobility for forming APD structure by the combination of phase-field (PF) simulations and transmission electron microscopy (TEM) observation [3]. Recently, additive manufacturing (AM) processes have attracted much attention because of their degrees of freedom in shapes. In addition, the laser powder-bed fusion (L-PBF) type AM process can fabricate single crystal parts by applying an optimum scanning strategy [4]. If Fe₃Al single crystals are fabricated by the L-PBF process, they will be useful in practical applications. However, the excess vacancies introduced by rapid cooling in the L-PBF process would affect the growth of APD, which is closely related to the mechanical properties of the fabricated single crystals. Fabricating Fe₃Al by L-PBF process is difficult due to cracks and defects [5]. Fe₃Al single crystals have not yet been fabricated by L-PBF process. In this study, we investigated the growth of APD in the laser-irradiated regions of the Fe-28at.%Al bulk by transmission electron microscopy (TEM) to reveal the effect of excess vacancies on APD growth. Also, we fabricated Fe₃Al block samples under various laser irradiation conditions and evaluated crystal orientation, solute segregation and the formation of defect, aiming to achieve superelasticity in Fe₃Al fabricated by L-PBF process. It was found that APD growth during ordering heat treatment is faster in the laser-irradiated and rapidly cooled than in water-quenched regions. Excess vacancies introduced by the rapid cooling are suggested to promote the APD growth of the Fe₃Al intermetallic phase. The ordering mobility calculated by phase-field simulations was smaller than that predicted using the amount of the excess vacancies induced in the laser-irradiation process, i.e., quenching from the solidus temperature. In the laser-irradiated region, a lot of dislocations were observed by TEM. It is implied that dislocations act as a sink for vacancies and reduce the effect of supersaturated vacancies. Block samples were fabricated by laser metal additive manufacturing equipment under a total of 110 conditions with various laser power, scanning speed, scan pitch, substrate temperature and scanning strategy. Crystal orientation analysis was performed by electron backscatter diffraction (SEM-EBSD). Elemental analysis was performed by energy-dispersive X-ray spectroscopy (SEM-EDS). EBSD orientation maps have revealed that the single crystal-like texture with &lt;100&gt; oriented in the X, Y and Z directions was fabricated. However, partial cracks originating from thermal stress were observed in the sample. EDS maps have shown that solute segregation did not occur, in accordance with the results of laser irradiation to bulk material [6], suggesting the occurrence of absolute stability.<br/><br/>[1] H.Y. Yasuda, T. Nakajima, K. Nakano, K. Yamaoka, M. Ueda, Y. Umakoshi, Acta Mater., 53, (2005), 5343–5351.<br/>[2] H.Y. Yasuda, K. Nakano, T. Nakajima, M. Ueda, Y. Umakoshi, Acta Mater., 51 (2003), 5101–5112.<br/>[3] Y. Liu, M. Watanabe, M. Okugawa, T. Hagiwara, T. Sato, Y. Seguchi, Y. Adachi, Y. Minamino, Y. Koizumi, Acta Mater., 273, (2024), 119958.<br/>[4] T. Ishimoto, K. Hagihara, K. Hisamoto, S.H. Sun, T. Nakano, Scr. Mater., 132, (2017), 34–38.<br/>[5] G. Rolink, S. Vogt, L. Senčekova, A. Weisheit, R. Poprawe, M. Palm, J. Mater. Res., 29, (2014), 2036–2043.<br/>[6] T. Sato, Y. Liu, M. Okugawa, K. Sato, H. Y. Yasuda, T. Nakano, Y. Koizumi, Abstract for JIM Autumn Meeting (2023), 96.