Effect of alloying elements on the structure and mechanical properties of NbMoTaWX (X = Cr, V, Ti, Zr, and Hf) refractory high-entropy alloys

Haibo Liu,Lei Liu,Cunlin Xin

doi:10.1063/5.0038405

Abstract

Numerous alloying elements can improve the mechanical properties of NbMoTaW refractory high-entropy alloys (RHEAs), but the relationship between the alloying of different elements and the changes in the microstructure and mechanical properties of RHEAs is ambiguous. The first principles based on density functional theory are used to calculate the lattice parameters, electronic properties, and elastic properties of NbMoTaW-based RHEAs to reveal the microstructure and mechanical properties of NbMoTaW RHEAs with alloying elements of the same period or subgroup. The melting point, lattice constant, and mass density of NbMoTaW-based RHEAs are controlled by the alloying elements such as Cr, V, Ti, Zr, and Hf. Valence electron concentration (VEC) is a key factor affecting the electronic structure and mechanical properties of NbMoTaW-based RHEAs. High VEC can improve the mechanical properties of RHEAs but reduce the ductility. Cr-alloying has a significant effect on mechanical properties of NbMoTaW RHEAs, and Ti has a significant effect on ductility. The orbital electronic interactions between the alloying elements and Nb, Mo, Ta, and W atoms shown by the density of states and electron density difference may explain the relationship between VEC and the mechanical properties of RHEAs. Our results provide the underlying insights needed to guide the design of NbMoTaW RHEAs with excellent mechanical properties.

Highlights

High-entropy alloys (HEAs) are composed of at least four or five elements with equal or almost equal molar ratios.1 HEAs are prone to form single-phase body centered cubic (BCC), face centered cubic (FCC), or hexagonal close-packed (HCP) structures and exhibit excellent material properties, such as high strength, hardness and wear resistance, corrosion resistance, and high temperature oxidation resistance.2–4 Among the numerous HEA systems, refractory high-entropy alloys (RHEAs) have attracted extensive attention due to their excellent thermal stability,5 high strength,6 and improved friction properties7 at high temperatures.Senkov8 first proposed a new type of RHEA in 2010: Mo25Nb25Ta25W25; it is completely composed of refractory metal elements
The Valence electron concentration (VEC), atomic size difference, melting point, lattice constant, and mass density of RHEAs are controlled by alloying elements
The mechanical properties of NbMoTaW RHEAs increase with the alloying of Ti, V, and Cr elements and are basically similar to the alloying of Ti, Zr, and Hf elements, but the toughness changes are opposite

Summary

Introduction

High-entropy alloys (HEAs) are composed of at least four or five elements with equal or almost equal molar ratios. HEAs are prone to form single-phase body centered cubic (BCC), face centered cubic (FCC), or hexagonal close-packed (HCP) structures and exhibit excellent material properties, such as high strength, hardness and wear resistance, corrosion resistance, and high temperature oxidation resistance. Among the numerous HEA systems, refractory high-entropy alloys (RHEAs) have attracted extensive attention due to their excellent thermal stability, high strength, and improved friction properties at high temperatures.Senkov first proposed a new type of RHEA in 2010: Mo25Nb25Ta25W25; it is completely composed of refractory metal elements. Among the numerous HEA systems, refractory high-entropy alloys (RHEAs) have attracted extensive attention due to their excellent thermal stability, high strength, and improved friction properties at high temperatures. NbMoTaW-based RHEAs have higher melting points and mechanical strength, excellent thermal stability, and high softening resistance at high temperature than nickel-based alloys and other superalloys.. NbMoTaW-based RHEAs have higher melting points and mechanical strength, excellent thermal stability, and high softening resistance at high temperature than nickel-based alloys and other superalloys.9,10 They are considered potential high-temperature load-bearing structure and thermal protection system material candidates in aerospace, nuclear energy, defense, metallurgy, and other fields of extreme environments at high temperatures.. Re0.5NbMoTaW alloys exhibit the best mechanical properties, and their yield strength and room temperature ductility are increased by 89 MPa and 4.4%, respectively, compared with NbMoTaW.

Methods

Results

Conclusion