INFLUENCE OF COMPOSITION AND MICROSTRUCTURE ON THE FEATURES OF MECHANICAL PROPERTIES OF Co-Cr-Fe-Mn-Ni HIGH ENTROPY ALLOYS

The structure and mechanical properties of high-entropy CoCrFeMnNi (equiatomic) and Co20Cr26Fe20Mn20Ni14 alloys, which differ significantly in the stacking-fault energy, are studied. The structure of the alloys was investigated in three states – as-cast, after homogenizing annealing at T = 1000 °C for 24h and after annealing at T = 850 °C. It was found that in the cast state and after homogenizing annealing at 1000 °C both alloys are single-phase solid solutions with a FCC lattice. Annealing at 850 °C preserves the single-phase state in the equiatomic CoCrFeMnNi alloy, but leads to the appearance of a σ-phase in the Co20Cr26Fe20Mn20Ni14 alloy. The mechanical properties of these alloys were studied in a single-phase state by uniaxial compression tests and hardness measurements. It was discovered, that both alloys in a single-phase state had high plasticity and tendency to force strain hardening. The behavior of hardening coefficients in the area of true strains e = 0.05 – 0.17 vary considerably. This may be due to a significant difference in the stacking-fault energy of the investigated alloys. As a result, in Co20Cr26Fe20Mn20Ni14 alloy along with dislocation deformation mechanism there is a high probability of implementation the twinning mechanism.