SYNTHESIS AND STRUCTURE OF FOUR TiZrVNb AND FIVE-COMPONENT TiZrHfVNb REFRACTORY HIGH-ENTROPY ALLOYS

High-entropy alloys attract researcher’s attention due to the presence of a set of new properties. The paper considers the factors affecting the structure of high-entropy alloys (HEAs) based on the elements Ti, Zr, Hf, V, and Nb. The structure data of four-component Ti₂₅Zr₂₅V₂₅Nb₂₅ and five-component Ti₂₀Zr₂₀Hf₂₀V₂₀Nb₂₀ alloys, which were obtained under the same melting and cooling conditions in an arc furnace, are presented. The data of the EDX analysis showed that the chemical composition of the alloys corresponded to the nominal one. Analysis of micrographs of the ingots surface allows us to conclude that the applied melting mode led to overheating of the four–component alloy, but not for the five-component one. It was experimentally found that the primary formation of the four-component alloy occurs faster than that of the five-component one, but further remelting under overheating conditions leads to multiphase structure formation. The maximum content of BCC solid solution (98%) in Ti₂₅Zr₂₅V₂₅Nb₂₅ alloy was achieved during the first remelting, another phase was FCC solid solution (2%). The maximum content of BCC solid solution (95%) in Ti₂₀Zr₂₀Hf₂₀V₂₀Nb₂₀ alloy was obtained by repeated remelting, BCC, HCP solid solutions, and the Laves phase were presented in the amount of 3% or less. The crystal lattice parameters of the BCC main phases for the Ti₂₅Zr₂₅V₂₅Nb₂₅ and Ti₂₀Zr₂₀Hf₂₀V₂₀Nb₂₀ alloys were 3.270 and 3.362 Å, respectively. It was established that to obtain refractory HEAs with a single-phase structure it is important both fulfilment of thermodynamic conditions and correct choice of time-temperature conditions of melting and crystallization for each specific alloy composition.