Sathiraj, G Dan
(2016)
Development of Microstructure and Crystalographic texture
during thermo-Mechanical Processing of Equiatomic CoCrFeMnNi High Entropy Alloy.
PhD thesis, Indian Institute of Technology Hyderabad.
Abstract
High entropy alloys (HEAs) are multicomponent alloys based on the novel alloy design concept of mixing a sufficiently large number of elements (more than five) in equiatomic or near equiatomic proportion. Remarkably, despite having the presence of a large number of components, the HEAs often show rather simple crystal structures, such as FCC (e.g. equiatomic CoCrFeMnNi), BCC or FCC+BCC. This rather surprising behaviour is explained on the basis of large configurational entropy of mixing, which increases with increasing number of the alloying elements according to the relationship ∆ S = - R∑n ln ∆ S = - R∑n ln (where n is the number of elements and R is the Universal gas constant). It has been argued that large increase in the configurational entropy can sufficiently lower the free energy, thereby stabilizing the HEAs into solid solution phases with simple crystal structures. HEAs have attracted considerable research interest which have resulted in the discovery of many interesting and unique properties of these materials. The origin of these unique properties in HEAs is attributed to the core effects of multicomponent solid solution formation, including distorted lattice structure, cocktail effect, sluggish diffusion and extensive formation of deformation nano-twins.
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