Mechanical alloying: a critical review

Mechanical alloying (MA) is a powder process that consists of repeated cold welding, fracturing, and rewelding of powder particles in a high-energy ball mill. This process is capable of synthesizing different types of non-equilibrium phases including supersaturated solid solutions, nanocrystalline materials, metallic glasses, high-entropy alloys, and several others. MA'd materials have found many applications. The present article critically reviews recent developments in emerging areas of nanostructured materials and nanocomposites, high-entropy alloys, alloys synthesized from immiscible elements, and heterostructured materials. Current challenges and future directions of research in the general area of MA are also indicated.