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Mechanical alloying (MA) is a powder processing technique used to produce alloy or composite powders with either equilibrium or non-equilibrium microstructures from elemental powders. This process takes place in a high-energy ball mill, where intense mechanical forces cause the powders to be repeatedly fractured, deformed, and cold-welded together. As the particles are broken and new surfaces are exposed, they undergo continuous mixing and bonding, leading to the formation of an alloy structure over time. Through repeated cycles of grinding and welding, the final goal of mechanical alloying—creating a homogeneous alloy—is achieved.
Developed in the late 1960s by Benjamin and his team at the United States International Nickel Corporation (INCO), mechanical alloying was initially used for producing nickel- and iron-based superalloys that combined precipitation hardening and oxide dispersion strengthening. In the early 1980s, American scientist Koch and colleagues successfully synthesized Ni60Nb40 amorphous powder using this method, marking a significant breakthrough. By the late 1980s, researchers like W. Schlümm and H. Grewe proposed that mechanical alloying could also produce nanocrystalline materials. Later, Fecht demonstrated the fabrication of ultrafine-grained alloys using MA, opening up a new field in material science.
Today, mechanical alloying has found widespread applications in the production of nanostructured materials, magnetic materials, superconductors, amorphous alloys, nanocrystalline materials, lightweight high-strength metals, and supersaturated solid solutions. Countries such as the United States, Germany, and Japan have invested heavily in research and development, achieving industrial-scale production. For instance, INCO has established a mechanical alloying line capable of producing 350 tons per year of iron, nickel, and aluminum oxide-dispersed alloys. In China, research on mechanical alloying began in 1988 and has made significant progress over the past two decades.
The basic principles of mechanical alloying involve complex mechanisms of particle deformation and atomic diffusion. In 1988, Japanese researcher Shinmiya Hideo proposed the rolling and refolding model, suggesting that repeated rolling can reduce the thickness of powder particles to extremely small sizes, enabling the formation of ultrafine structures. Another theory, introduced by Atzmon in 1990, involves the mechanically induced self-propagating reaction mechanism, where intermetallic compounds form suddenly due to localized high temperatures generated during ball milling. These high-energy collisions can "ignite" the powder, triggering rapid alloy formation.
Currently, it is widely accepted that mechanical alloying is primarily governed by diffusion processes. The key steps include continuous mixing, crushing, and cold welding of powder particles. During ball milling, high-density dislocations form, and grain sizes gradually refine to the nanoscale. This provides a fast diffusion pathway for atoms, allowing the formation of alloy nuclei under appropriate conditions. As the process continues, all elemental powders eventually combine into a single alloy phase, which grows and stabilizes over time.