Composition formation in dendrites in cast multicomponent high-entropy monophase alloys with BCC crystal lattice

Abstract

By methods of the structural analysis —X-ray phase, a raster electronic microscopy, local Auger-electron spectroscopy, electron-ray X-ray microanalysis; and also mechanical tests — low-temperature (20 °С) and high-temperature (20—1000 °С) short-term (1 minute) and long (60 mines) indentations, high-temperature test for uniaxial compression and extension the distribution of elements in cast multicomponent monophase high-entropy alloys (HEAs) with BCC crystal lattice are studied and their mechanical properties are defined. On the studied alloys it is shown that monophase substitutional solid solution with BCC crystal lattice are formed at a variation for compositions of cast equiatomic  HEAs, allowing to change electron concentration within 4,60—7,20 el/atom. For investigated BCC-HEYs the dendrite segregation is characteristic: axes of dendrites are enriched by BCC-metals with the highest melting temperature in an alloy. At the same time interdendritic areas contain in the greatest quantity less refractory metals. The parametre of a crystal lattice of the BCC-phase in monophase HEYs is closest to lattice parametre of BCC-metal in an alloy with highest melting temperature. Relative difference is in limits of O—0,8%. The method of local Auger-electron spectroscopy (diameter of a stain of an analysed surface made 8— 10 nanometers) allows to analyse a dendrite segregation most distinctly. The method X-ray microanalysis (the investigated volume of an alloy made ~3x3 micron) "averages" defined concentration of elements in an alloy, approaching their values to burdening equiatomic. Studied HEYs have the raised values of mechanical characteristics at high temperatures.