Mechanical alloying of high-entropy alloys: Process optimization, microstructural evolution and multifunctional applications

High-entropy alloys (HEAs) have attracted increasing interest for extreme-environment applications because of their high strength, corrosion resistance, thermal stability, and functional tunability. Mechanical alloying (MA) is a solid-state powder metallurgy route that enables the fabrication of chemically homogeneous, nanostructured, and metastable HEAs while avoiding segregation and solidification defects associated with liquid-phase processing. This review critically examines MA-derived HEAs by linking milling parameters, powder evolution, consolidation routes, microstructural development, and multifunctional performance. Unlike previous reviews that mainly summarize MA-HEA systems or specific MA-spark plasma sintering (SPS) routes, this work emphasizes cross-parameter statistics, energy-transfer coupling, contamination pathways, and structure-function relationships. The effects of milling time, milling speed, ball-to-powder ratio (BPR), process control agents, and milling atmosphere on alloying kinetics, phase formation, particle refinement, powder recovery, and contamination are systematically evaluated. Statistical analysis shows that milling speeds of 300–400 rpm and a BPR of 10:1 are the most employed conditions, while the median alloying time is approximately 40 h. These findings are interpreted through an energy-transfer framework, highlighting that effective alloying energy, rather than nominal milling intensity, governs MA efficiency. SPS and vacuum hot pressing sintering (VHPS) are compared as major consolidation routes, and MA-derived coatings are discussed for protective and functional applications. Mechanical, corrosion, thermal, and functional properties are reviewed across structural, catalytic, hydrogen-storage, magnetic, electromagnetic absorption, and thermoelectric applications. Future priorities include contamination control, scalable densification, microstructure retention, in situ characterization, database construction, CALPHAD-assisted screening, and machine-learning-guided alloy design.