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High-entropy alloys (HEAs)
High-entropy alloys (HEAs) are alloys with five or more principal elements.Each principal element should have a concentration between 5 and 35 at.%. HEAs are a new class of multi-component equiatomic (or near equiatomic) alloys, which form simple solid solutions due to their high configurational entropy.These alloys are currently the focus of significant attention in materials science and engineering because they can have desirable properties. These alloys are named ‘HEAs’ because their liquid or random solid solution states have significantly higher mixing entropies than those in conventional alloys.the higher mixing entropy in these alloys facilitates the formation of solid solution phases with simple structures and thus reduces the number of phases.High entropy alloys possess exceptionally high strength/hardness, outstanding wear resistance, exceptional high-temperature strength, good structural stability, good corrosion and oxidation resistance.

High-entropy effect
The high-entropy effect states that the higher mixing entropy (mainly configurational) in HEAs lowers the free energy of solid solution phases and facilitates their formation, particularly at higher temperatures. There are nearly 30 elements used in production of over 300 alloys. Typically used metals are Iron, Nickel, Copper, Aluminium, chromium, Cobalt, Manganese, Titanium, Tantalum, Silicon etc.

Production of HEAs
Production of High entropy alloys is mainly through two routes. First one is by melting casting route which is vacuum arc-melted from the starting elements with purities higher than 99.9% and then cast into billets. Second route is by Mechanical Alloying (by High Energy Ball Milling) of high purity (>99.5 wt.%) metallic powders (with particle size less than 45 microns) mixed in equiatomic composition and milled in a planetary ball-miller for 10- 100 hours in an inert atmosphere and then sintered by spark plasma sintering. By using powder metallurgy route we get nano-crystalline structure which have superior properties over conventional materials in use. High Entropy Alloys mainly have BCC(Body Centered Cubic lattice ) and/or FCC (Face Centered Cubic lattice) structure.

Uses of HEAs
HEAs because of their high form-ability and strength combined with low density will serve as the future advanced materials and are expected to replace super alloys in energy sectors and aero-space applications. Because HEAs are the cocktail of metallic elements a wide range of materials can be produced which can serve the future requirements at a lower cost with superior mechanical properties.