Effect of Nano-Al2O3 reinforcement on the microstructure and tribological behavior of AlCoCrFeNi high entropy Alloy: A comparative study with Micro-Al2O3

In this study, the effects of adding 5, 10, and 15 wt% nano-Al 2 O 3 reinforcement on the microstructural evolution and tribological behavior of AlCoCrFeNi high-entropy alloy (HEA) were systematically examined and compared with micro-Al 2 O 3 reinforced samples. The alloying process was carried out by mechanical alloying (MA) for 30 h, followed by Spark Plasma Sintering (SPS) at 1000 °C with a 5 min holding time. The mechanically alloyed powders exhibited a single BCC phase, while after SPS, a dual-phase structure containing both BCC and FCC phases was formed. Microstructural characterization was performed using FESEM imaging, EDS elemental mapping, and XRD analysis. The addition of nano- Al 2 O 3 led to a distinct island-like morphology and slight variations in phase fractions. Microhardness measurements showed values of 509, 517, and 603 HV for 5, 10, and 15 wt% nano- Al 2 O 3 additions, respectively, compared with 690 HV for the unreinforced alloy. Micro- Al 2 O 3 reinforced samples exhibited higher hardness, reaching up to 999 HV at 15 wt% due to increased BCC phase content and improved particle dispersion. The wear rate initially increased from 6.18 × 10 −3 to 10.94 × 10 −3 mm 3 /N.m with reinforcement addition but decreased to 4.79 × 10 −3 mm 3 /N.m at 15 wt%. These findings highlight the influence of reinforcement particle size and content on the microstructure, hardness, and wear behavior of the AlCoCrFeNi HEA system.