Differential Thermal Analysis to Assist the Design of Corrosion-resistant High Entropy Alloys for Laser Powder Bed Fusion

In this study, Al, Cr, Fe, Mn, and Ni are selected and pure elemental powders were used to prepare several medium entropy alloys (MEAs) and high entropy alloys (HEAs). Differential Thermal Analysis (DTA) is used as a tool for pre-screening of the compositions suitable to design corrosion-resistant alloys for Laser Powder Bed Fusion (LPBF). The advantage of DTA lies in the precise temperature control and in the small quantity of powder necessary to perform the test in near-equilibrium conditions. The powder mixtures were heated up to 1550°C, fully melted, and then cooled down to room temperature at 5°C/min. The results of DTA are used as reference to understand the complex microstructures obtained using LPBF.
Microstructure analysis of DTA samples by combining Optical Microscopy (OM) and Scanning Electron Microscopy (SEM) helped to confirm the phase prediction theories. Most of the samples showed a heterogeneous structure with Ni-Al rich B2 phase, Fe-Cr rich BCC and FCC phases. The spinodal decomposition of the BCC phase was also observed in the equimolar AlCrFeMnNi sample. The Valence Electron Concentration (VEC) theory was verified and the partitioning of the elements between the phases was investigated.