Advanced characterization of two novel Fe-rich high entropy alloys developed for laser powder bed fusion in the Al-Co-Cr-Fe-Ni-Zr system

Abstract

Laser powder bed fusion (LPBF) was used to manufacture two high entropy alloys (HEAs) within the Al-Co-Cr-Fe-Ni-Zr system. The selected compositional ranges were similar to alumina forming austenitic (AFA) steels but omitting interstitials and replacing Nb with Zr as the Laves forming element. The Fe-rich austenitic HEAs were prepared with varying Al and Zr content to evaluate the influence on the presence, size, and distribution of the intermetallic (IM) precipitates. The LPBF process combined with a single (950 °C 6 h) heat treatment formed large, elongated grains with a fine dispersion of multiple different nano-sized IM phases. Synchrotron high energy x-ray diffraction (HEXRD) revealed the cubic M₂₃Zr₆ as the main Zr-rich IM phase, stabilized by the multi-element mixture (M=Co, Fe, Ni) and the high cooling rates of the LPBF process. Further HEXRD in-situ compression was performed from room temperature to 900 °C to evaluate the phase stability, thermal expansion, and the strength contribution of the austenitic matrix and the M₂₃Zr₆ and NiAl B2 IM phases. The evolution of lattice strain and full width at half maximum of the reflexes was tracked using a statistical model, enabling quantitative analysis along the deformation.