Generation of increased mechanical properties of Cantor high­entropy alloy

Abstract

The article considers a brief review of the last years of Russian and foreign research on the possibilities of improving mechanical properties of the Cantor quinary high­entropy alloy (HEA) with different phase composition in wide temperature range. The alloy, one of the frst created equimolar HEAs with FCC structure, needs mechanical properties improvement in accordance with possible felds of application in spite of its high impact toughness and increased creep resistance. It has been noted that bimodal distribution of the grains by sizes under severe plastic torsional strain at high pressure of 7.8 GPa of cast alloy and subsequent short­time annealing at 873 and 973 K can change strength and plastic properties. Nanodimensional scale of the grains surrounded by amorphous envelope has been obtained for HEA produced by the method of magnetron sputtering and subsequent annealing at 573 K. In such a two­phase alloy nanohardness amounted to 9.44 GPa and elasticity modulus – to 183 GPa. Using plasticity effect induced by phase transformation in (CrMnFeCoNi)50Fe50 alloy obtained by the method of laser additive technology the ultimate strength of 415 – 470 MPa has been reached at high level of plasticity up to 77 %. It has been ensured by FCC → BCC diffusionless transformation. It is shown that difference in mechanisms of plastic strain of cast alloy at 77 K and 293 K (dislocation glide and twinning) determines a combination of increased “strength­plasticity” properties. Samples for generation of twins prestrained at 77 K exhibit increased strength and plasticity under subsequent loading at 293 K in comparison with the unstrained ones. For HEA obtained by laser additive technology this way of increasing properties is also true. The way of improving mechanical properties at the expense of electron beam processing is noted. The attention is paid to the necessity of taking into account the role of entropy, crystal lattice distortions, short­range order, weak diffusion and “cocktail” effect in the analysis of mechanical properties.