Microstructure and Properties of Ultrafine-Grained AlCoCrFeNi2.1 High-Entropy Alloy Fabricated by Mechanical Alloying and Spark Plasma Sintering

AlCoCrFeNi2.1 high-entropy alloys (HEAs) with ultrafine-grained microstructures are still challenging to produce using conventional casting methods. Here, we report a straightforward method for fabricating ultrafine-grained HEAs by combining mechanical alloying (MA) and spark plasma sintering (SPS). A systematic investigation was conducted to examine the effects of MA parameters on the alloying behavior and its evolution in HEA powders, as well as the influence of sintering temperature on the microstructure and mechanical properties of the sintered HEAs. The results indicate that the optimal performance of the HEA was achieved with a milling speed of 350 rpm, a ball-to-powder ratio of 20:1, and a milling duration of 42 h, combined with a sintering temperature of 1150 degrees C. Microstructural analysis reveals that the alloy predominantly comprises similar to 65 vol% FCC phase and similar to 35 vol% BCC phase, consistent with the phase volume fraction produced by casting. The MA and sintering parameters significantly impact the hardness and compressive strength of the HEAs. Under optimized conditions, the Vickers hardness of the sintered HEA reaches 646 +/- 15 HV, with a compressive fracture strength of 2256 +/- 51 MPa, attributed to the equiaxed ultrafine grains of both FCC and BCC phases.