Microstructure and mechanical properties of AlCoCrFeNi2.1 eutectic high-entropy alloy synthesized by spark plasma sintering of gas-atomized powder

Eutectic high-entropy alloys (EHEAs) are usually prepared by melting method. Here, bulk eutectic high-entropy alloys, AlCoCrFeNi2.1, with a phase constitution of FCC and BCC phases, was successfully prepared by spark plasma sintering using gas-atomized powders as starting materials. With the increase of sintering temperature, a gradual microstructure evolution from lamellar eutectic to massive eutectic was observed, which should be caused by the decrease of surface energy. When sintering temperature was 1200 °C, the lamellar eutectic microstructure was completely transformed into a massive eutectic microstructure. The bulk EHEA shows the best mechanical performance when the sintering temperature is 1000 °C. The compressive yield strength, fracture strength, and ductility reached 758.60 MPa, 2626.29 MPa, and 45.45%, respectively. Furthermore, the tensile yield strength, fracture strength and ductility reached 538.13 MPa, 963.55 MPa, and 13.31%, respectively. The improved properties can be attributed to phase interfaces between FCC and BCC, and lamellar microstructures in EHEA, strengthening the alloys by inhibiting dislocation motion. The hardness of the alloy sintered at 1000 °C also reached a maximum value of 294.3 HV at 1000 °C, which has the best wear resistance, and the wear mechanism was adhesive wear. The phase interface orientation relationship of AlCoCrFeNi2.1 EHEA satisfies the N-M relationship, which is < 110>FCC//<100>BCC,{111}FCC//{110}BCC.