Simulation guided in-situ alloying in the medium entropy Fe-Ni-Nb system via Laser powder bed fusion

Medium entropy alloys (MEAs) with multiphase microstructure offer a promising combination of strength and ductility. Identifying potential compositions for additive manufacturing from a huge compositional domain is challenging. CALPHAD based Thermo-Calc® simulations are carried out to identify potential compositions; three alloys are selected within the ternary Fe–Ni–Nb MEA system, to explore hypo and hyper eutectic conditions. The solidification pathway is simulated using Scheil’s model with solute trapping at different solidification velocities for in-situ alloying in Laser Powder Bed Fusion (PBF-LB/M), predicting FCC and Laves phases to be present based on the Nb content and laser scan speed. The results were validated through single-track experiments and Energy-dispersive X-ray spectroscopy (EDX) Despite its high melting point, Nb was successfully alloyed with the Fe and Ni powders. The Key-hole mode and remelting proved effective to increase intermixing of the elements. Most uniform distribution of elements was observed in hypo eutectic compositions, which confirms the in-situ alloying strategy adopted for fine tuning the multicomponent compositions. Cracking in the weld tracks was observed in hyper eutectic compositions due to the primary Laves phase formation. Finally, High-speed ratio pyrometry was applied to monitor the thermal history during laser-material interaction and calculate the apparent cooling rates, which ranged between the 104 and 106 °C/s. The combined experimental and computational approach provides a foundation for controlled in-situ alloying in the Fe–Ni–Nb system and predictive alloy design. The current study confirms simulation-guided additive manufacturing for the development of tailored medium entropy alloys.