FGM-derived phase and property mapping for accelerated alloy design in additively manufactured high-entropy alloys

This study proposes a functionally graded material (FGM)-derived mapping strategy for accelerating alloy design in metal additive manufacturing, using the Co–Cr–Fe–Mn–Ni–Al system as a model alloy. A compositionally graded specimen was fabricated by directed energy deposition through layer-wise control of CoCrFeMnNi high-entropy alloy and Al powder feed rates. Because the nominal and deposited compositions differed owing to powder-flow and catchment-efficiency differences, all phase and property maps were anchored to EDS-measured local compositions. The as-built gradient revealed a composition-dependent transition from an FCC-dominant structure to a BCC/B2-dominant structure near 7.5–10 at% Al, accompanied by a rapid increase in hardness from ∼200 HV to >500 HV. Macro-cracking initiated near ∼12 at% Al under the present processing condition, defining an approximate upper boundary for the crack-free composition window. EBSD- and XRD-assisted mapping, combined with heat treatments between 700 and 1100 °C, enabled the construction of composition–temperature maps for phase fraction, grain size, hardness, and specific hardness. These maps identify a promising 10–12 at% Al range in which phase-driven hardening is achieved before severe macro-cracking occurs. The proposed FGM-derived mapping approach provides a practical and material-efficient route for establishing process-dependent phase/property maps in AM alloys, while also highlighting the importance of composition anchoring and complementary nanoscale phase characterization.