Properties of the Zr-doped CrCoMnFeNi high-entropy alloy after high-pressure torsion

The single-phase CoCrFeMnNi high-entropy alloy (HEA) possesses a face-centered cubic lattice. Its strength and ductility at room and elevated temperatures are insufficient to compete with stainless steels or titanium- and nickel-based alloys. However, it is possible to increase its strength by adding dispersion hardening oxide, nitride or carbide particles. Such particles being inside the metallic matrix grains can impede the movement of dislocations. In this work, a study of the HEA Cantor alloy CoCrFeMnNi with the addition of 1 wt.% zirconium was carried out. Zirconium forms fine oxide particles in the alloy and does not dissolve in the matrix. It is shown that the alloy is thermally stable in the temperature range from 500 to 1000°C, its phase composition and lattice parameter do not change. The microhardness of the material also varies slightly depending on the heat treatment. A slight increase in hardness from 154 HV in the as-cast state to 172 HV occurs after annealing at 750°C. The three-point bending tests showed an increase in Young’s modulus from 109 to 166 MPa with an increase in the annealing temperature from 500 to 1000°C. The conditional tensile strength has a minimum of 380 MPa in the sample annealed at 750°C. The sample of CoCrFeMnNi alloy + 1 wt.% Zr subjected to high pressure torsion showed a significant increase in hardness compared to the initial sample, almost 3 times, and the conditional tensile strength increased by almost 6 times. However, the phase composition and lattice parameter of studied alloy have not changed.