Hot Working of an Fe-25Al-1.5Ta Alloy Produced by Laser Powder Bed Fusion

Abstract

In the present work, hot working was used as a post-processing method for Fe-25Al-1.5Ta (at.%) alloy built using laser powder bed fusion (LPBF) to refine the undesirable columnar microstructure with heterogeneous grain sizes and strong textures in the build direction. The hot deformation behavior and workability were investigated using constitutive modeling and the concept of processing maps. Uniaxial compression tests were conducted up to a true strain of 0.8 at 900 °C, 1000 °C, and 1100 °C with strain rates of 0.0013 s−1, 0.01 s−1, and 0.1 s−1. The constitutive equations were derived to describe the flow stress–strain behavior in relation to the Zener–Hollomon parameter. Processing maps based on a dynamic materials model were plotted to evaluate the hot workability and to determine the optimal processing window as well as the active deformation mechanisms. The microstructure of the deformed specimens was characterized by scanning electron microscopy equipped with an electron backscatter diffraction detector. The results indicated a high degree of hot workability of the LPBF builds without flow instabilities over the entire deformation range tested. The epitaxially elongated grains of the as-built alloys were significantly refined after deformation through dynamic softening processes, and the porosity was reduced due to compressive deformation. The current study revealed a well-suited parameter range of 1000–1080 °C/0.004–0.012 s−1 for the safe and efficient deformation of the LPBF-fabricated Fe-25Al-1.5Ta alloys. The effectiveness of the process combination of LPBF with subsequent hot forming could be verified with regard to microstructure refinement and porosity reduction.