Makarenko O. Features of structural-phase transformations and thermal stability of high-entropy alloys Cr–Fe–Сo–Ni and VNbTiHfZr coatings

The dissertation is devoted to solve of the urgent scientific and technical development problem of high-entropy alloys based on CrFeCoNi system and coatings VNbTiHfZr at the research of phase composition and mechanical properties both in the initial state, and influence of temperature (high-temperature X-ray diffraction (HT XRD) and annealing). A comprehensive study of phase transformations of high-entropy alloys and coatings was performed using X-ray diffractometry (both at room temperature and in situ), scanning, transmission and optical electron microscopy, energy dispersive X-ray fluorescence analysis and microindentation. The effect of aluminum on the phase composition, microstructure, physical and mechanical properties of the high-entropy CrFeCoNiVAlx system (x = 0; 0.5; 1; 2; 3) both in the initial state and after annealing (1073, 1173, 1273 and 1373 К for 2 h in vacuum) was investigated. Using high-temperature in situ X-ray diffractometry established a change in the phase composition of multicomponent HEAs with different structures and investigates a change in their coefficient of linear thermal expansion. The influence of deformation on the physical and mechanical properties and wear resistance of the two-phase HEA Cr20Fe25Co10Ni20Mn15Al10, which crystallizes in solid solutions with B2 and FCC lattices was research. It was found that high-entropy single-phase nitride VNbTiHfZr coatings are thermostable after annealing at 1273 K for 1 h. The modulus of elasticity is 530–670 GPa and microhardness 50–66 GPa. Keywords: high-entropy alloys; high-entropy coatings; X-ray diffractometry; solid solutions; microhardness; coefficient of thermal expansion; phase composition; deformation.