Excellent mechanical properties and unique phase transformation in an additively manufactured high-entropy alloy

High-entropy alloys (HEAs) consist of multiple principal elements with concentrations between 5 and 35 at%. HEAs have attracted considerable interest as structural materials due to their reported superior strength, ductility, wear resistance, and corrosion resistance among other properties. Precipitation hardening is a more effective approach to increasing the strength of HEAs to useful levels than solid-solution strengthening especially for elevated-temperature applications. Additive manufacturing (AM) is a novel fabrication method for making near-net shape parts, but it has been sparsely used to fabricate HEAs, especially precipitation-strengthened ones. AM shows promise in achieving high-strength and ductility with faster precipitation kinetics, with some system exhibiting precipitates after 3D printing.

A precipitation-strengthened HEA, (Fe_0.3Ni_0.3Mn_0.3Cr_0.1)₈₈Ti₄Al₈, was developed and produced via conventional manufacturing with high strength but low ductility, due to an extensive network of brittle intermetallics that formed after prolonged artificial aging. As additive manufacturing (AM) can often drastically change the microstructure and properties of alloys, this HEA was also printed using laser powder bed fusion. Results indicated that excellent tensile properties were achieved using AM, owing to the unique thermal history and accordingly phase transformation during AM, enabling desirable microstructure, which was characterized using advanced techniques. The as-printed samples showed fine grain sizes and a high dislocation density. In addition, multiple passes during the printing induced intermetallic precipitates, which did not form a brittle network. The printed samples also exhibited unique precipitation behavior and kinetics during artificial aging, compared to conventionally manufactured counterpart.