Mechanical Alloying and Spark Plasma Sintering of Equiatomic AlCoCrFeMnNi High Entropy Alloy

In this research, a high entropy alloy of AlCoCrFeNiMn is made through mechanical alloying and the spark plasma sintering processes. Ball milling was done at different times of 12 h, 36 h, and 48 h in a cup with a diameter of 20 cm. Ball to powder percent weight of 10:1 was selected. X-ray diffraction patterns indicate the formation of solid solution microstructure after 48 h. The crystal size decreases from 23 to 16 nm with increasing milling time. The lattice strain of the structure increments from 0.3 to 0.68% with increasing time up to 48 h. SEM images clearly show the phenomenon of powder agglomeration and the absence of intermetallic compounds or brittle, complex structures. It is observed that with increasing ball-milling time, homogenization of powders increases, and the body-centered cubic phase is formed in the structure. The mechanically alloyed powders were consolidated spark plasma sintered at 700, 900, and 1000 °C. 50 MPa pressure, argon gas as atmosphere, and ten minutes as sintering time were selected as the sintering process parameters. The X-ray diffraction pattern shows that the structure of consolidated high entropy alloy has face-centered cubic and body-centered cubic phases. After sintering by the spark plasma method, the density of powders was measured by Archimedes’ rules, and the value was determined as 99% of theoretical density. The structure was without porosity. The hardness was measured using the microhardness Vickers test. Loading force was 50 g and loading time was seven seconds. The highest hardness was about 649 HV0.05.