Structural-Phase State of Nanocrystalline Al-based High-Entropy Alloys with Transition Elements

X-ray diffractometry, microstructural analysis and microhardness measurements have been carried out to study phase formations in the equiatomic high entropy alloys of the AlCoCuFeNiCr system of different chemical compositions. Thermodynamic and structural criteria are considered for predicting the alloys phase composition. It is shown that in AlCoCuFe, AlCoCuFeNi and AlCoCuFeNiCr, two-phase mixtures of solid solutions with bcc and fcc lattices are formed. With a decrease in the fraction of Al atoms, there is a tendency to disorder the solid solution of the bcc phase. That alloys are characterized by a dendritic structure in which the Cu-rich fcc phase is released in the intervals between the dendrites of the main bcc phase. Correlation of microhardness of alloys with volume fractions of phase components and their thermodynamic characteristics has been revealed.