Influences of Milling Time and NbC on Microstructure of AlCoCrFeNi2.1 High Entropy Alloy by Mechanical Alloying

AlCoCrFeNi2.1 eutectic high entropy alloy (EHEA) and AlCoCrFeNi2.1-xNbC (x=2.5wt%, 5.0wt%, 7.5wt%, and 10wt%) high entropy alloy (HEAs) were prepared by mechanical alloying (MA). The effects of milling time and NbC content on the alloying behavior and grain size of the AlCoCrFeNi2.1 EHEA were investigated. The experimental results show that the AlCoCrFeNi2.1 EHEA primarily consists of order BCC (B2) and face-centered-cubic (FCC) phases, while the AlCoCrFeNi2.1-xNbC (x=2.5wt%, 5.0wt%, 7.5wt%, and 10wt%) HEAs are composed of B2, FCC, and NbC phases. With the increase of milling time, the powder goes through three stages, irregularity, cold welding fracture and spheroidization. The particle size of AlCoCrFeNi2.1 EHEA powder shows a trend of first increasing and then decreasing. Therein, the particle size presents a normal distribution during 0-50 h alloying. With the addition of NbC, the AlCoCrFeNi2.1-xNbC HEAs powders are significantly refined. And the degree of grain refinement gradually increases with the increase of NbC content.