Strength and Plasticity of Cast Solid-Soluble High-Entropy Alloys

The strength properties of cast solid-solution high-entropy alloys based on bcc and fcc lattices in the temperature range from -70 to 900°C have been investigated. Melting ingots weighing up to 200 g were carried out in a vacuum-arc furnace MIFI-9 by melting the mixture in an atmosphere of purified argon with a non-consumable tungsten electrode on a water-cooled copper hearth. The X-ray phase analysis and scanning electron microscopy in combination with INCA X-ray microanalyzer were used. Hardness (HIT) and reduced elastic modulus (Er) were determined using automatic microindentation on a Micron-gamma device using the Berkovich pyramid with a 2 N load in accordance with ISO14577-1:2015. High-temperature indentation of the Vickers pyramid was carried out at a 9.8 N load in vacuum. Thehigh-entropy composition of Nb1.5Cr1.25MoV0.75Ta0.5, which is a solid solution based on the bcc lattice, is characterized by high values of hardness up to 900°C. The yield stress and plasticity of solid-solution alloys are determined depending on the temperatures of the compression tests and the type of crystal lattice. For the high-entropy composition TiZrHfVNbTa based on the bcc lattice, the yield points are almost twice as high as those of the CrMnFeCoNi composition based on the fcc lattice. To create high-entropy alloys with improved characteristics of hot hardness, it is necessary to take into account such factors as the melting point, enthalpy of mixing, and dimensional mismatch in the lattice. It was found that alloys based on bcc lattice at positive values of the enthalpy of mixing are characterized by high characteristics of plasticity and deformability, as well as normalized hardness HIT/Er and compressive yield strength at room temperature. This can be attributed to the cluster structure and distortion of the crystal lattice.