Local Nanostructure in Multicomponent High-Entropy Materials

Abstract

AbstractMulticomponent phase space contains extended regions of random or near-random multicomponent solid-solution single phases, stabilised by a relatively large configurational entropy of mixing that can often (though not always) suppress compound formation between the different atomic species. The present paper shows that there are very extensive variations of local nanostructure, local atomic clusters and associated local lattice strains within multicomponent high-entropy solid-solution single phases such as the fcc Cantor alloys, bcc Senkov alloys and rock-salt-structured Rost mono-oxides, even when there is no short-range ordering, i.e. even when the solid solution is completely random or ideal. There are, for instance, many billions of different local nanostructures and different local atomic clusters in equiatomic five-component fully random solid-solution single-phase materials such as the original fcc Cantor alloy CrMnFeCoNi and the original bcc Senkov alloy VNbMoTaW, extending over distances of many microns, with associated fluctuating hydrostatic and shear lattice strains of several percent. The number and extent of the variations in local nanostructure, atomic clusters and lattice strains increase dramatically to even higher values with increasing number of components in the material. The present paper also shows that there are similar variations in local nanostructure, local atomic clusters and associated local lattice strains surrounding point defects such as vacancies, line defects such as dislocations and planar defects such as grain boundaries and external surfaces, influencing many important material properties such as diffusion, plastic flow, recrystallisation, grain growth and catalysis. The number and extent of the variations in local nanostructure, atomic clusters and lattice strains make it difficult to have too much confidence in structures and properties of multicomponent high-entropy materials calculated using ab initio and other atomistic computer modelling techniques, since these techniques are restricted to relatively small numbers of atoms and are unable to sample effectively the full range of local structures and properties.