A Comparative Study of Microstructure and Hot Deformability of a Fe–Al–Ta Iron Aluminide Prepared via Additive Manufacturing and Conventional Casting

Abstract

In this work, the microstructure and hot deformation behavior of laser powder bed fusion (L-PBF) and conventionally cast Fe-25Al-1.5Ta (at.%) alloys were compared. The L-PBF builds recrystallized comparably to the as-cast samples during hot deformation. Nevertheless, distinct differences were observed in the flow behavior characteristics between the as-cast and L-PBF samples. The L-PBF builds exhibited lower flow stress than the as-cast material over the entire deformation conditions tested. The average activation energy of hot deformation (Q) of 344 kJ mol−1 was calculated for the L-PBF build and 385 kJ mol−1 for the cast material. The lower Q indicates lower deformation resistance of the L-PBF sample. The peak work hardening rate (θ) in the L-PBF sample (1.72 × 103 MPa) was significantly smaller than that of the as-cast sample (3.02 × 103 MPa), suggesting that the dislocation glide in the L-PBF sample is less hindered during deformation. Possible sources of the observed differences in the deformation behavior between the L-PBF and cast materials will be discussed. Initial and post-deformation microstructures were characterized using an X-ray diffractometer (XRD) and ultra-high-resolution scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDX) detector. The C14-(Fe, Al)2Ta Laves phase (P63/mmc) was predominantly formed at the A2 α-(Fe, Al) matrix phase grain boundaries in both the as-cast and L-PBF materials. The XRD results suggest that the ordering transition from B2-FeAl to a D03-Fe3Al phase occurs during casting, but rarely during ultra-high-cooling L-PBF processing. In summary, the L-PBF creates samples that are subject to less work hardening and require less deformation resistance, and thus, can be formed by a lower deformation force. It, in turn, reduces the loads imposed on the tooling and dies during the deformation processing, contributing to less wear and the high durability of dies.