A precipitation-hardened high-entropy alloy with excellent mechanical properties additively manufactured by in-situ alloying

Studies on precipitation-hardened high-entropy alloys (PHEAs) have demonstrated high strength, good ductility, and thermal stability, making them excellent candidates for high-temperature structural applications such as nuclear reactors. However, many complex parts for those applications would need to be produced via additive manufacturing (AM), whose rapid cooling rates and multiple heating cycles could change the microstructure of the chosen alloys and accordingly their mechanical properties. A PHEA, (Fe_0.3Ni_0.3Mn_0.3Cr_0.1)₈₈Ti₄Al₈, which was developed and produced via conventional manufacturing in our previous work with high strength but low ductility, was chosen to test the effects of AM on the microstructure and mechanical properties. Scanning electron microscopy, transmission electron microscopy, atom probe tomography, and X-ray diffraction were used to characterize the microstructure after printing and after aging. The as-printed sample exhibited fine grains (4.9 μm), a high dislocation density (1.22∗10¹⁴/m²), and small amounts of precipitates and inclusions, which resulted in an excellent combination of 1397 MPa ultimate tensile strength and 16 % ductility. Aging produced a complex four-phase microstructure consisting of L1₂ nanoprecipitates and a network of B2 and χ on grain boundaries. Strengthening analyses indicate that while grain size, dislocation density, and precipitates played a role in all samples, the as-printed strength was mainly due to fine grains, and the aged strength was dominantly owing to L1₂ nanoprecipitates. This work studies the effect of AM thermal history on PHEA microstructures, and provides a possible way to improve properties of PHEAs using AM.