Enhanced Mechanical Properties Using Annealing Treatment of AlCoCrFeNi 2.1 Fabricated via Plasma Arc Additive Manufacturing

Eutectic high‐entropy alloys (EHEAs) combine excellent high‐temperature stability and superior mechanical properties, making them promising candidates for extreme environmental applications. This study investigates the microstructure evolution and mechanical response of plasma arc additive manufactured AlCoCrFeNi 2.1 under different annealing treatments. Systematic characterization reveals temperature‐dependent phase transformations and microstructural modifications. Annealing at 500°C induced a phase transformation from face‐centered cubic (FCC) to body‐centered cubic (BCC) structure, accompanied by a measurable increase in BCC phase content. Elevated to 800°C, columnar lamellar eutectic structures exhibit widened interlamellar spacing accompanied by FCC phase growth and precipitation of fine spherical BCC particles within FCC domains. High‐temperature annealing at 1100°C induces BCC phase spheroidization and coarsening, along with complete dissolution of secondary precipitates. The mechanical properties demonstrate temperature‐dependent behavior: Hardness and strength follow an initial increase followed by reduction, while plasticity progressively improves. Optimal annealing at 1100°C achieves remarkable plasticity (23.6%) while maintaining high strength (tensile strength: 1137.23 MPa, yield strength: 595.51 MPa), realizing an exceptional strength‐plasticity synergy. This enhancement mechanism primarily originates from coarsening of the lamellae eutectic structure and the increase of the FCC phase. The findings establish a practical thermal treatment strategy to balance conflicting mechanical properties in plasma arc‐deposited HEA systems.