First-principles study of the energetics and the local chemical ordering of tungsten-based alloys

Tungsten (W) is considered a leading candidate for structural and functional materials in future fusion energy devices. The most attractive properties of tungsten for magnetic and inertial fusion energy reactors are its high melting point, high thermal conductivity, low sputtering yield, and low long-term disposal radioactive footprint. However, tungsten also presents a very low fracture toughness, primarily associated with inter-granular failure and bulk plasticity, limiting its applications. In recent years, several families of tungsten-based alloys have been explored to overcome the aforementioned limitations of pure tungsten. These might include tungsten-based high-entropy alloys (W-HEAs) and the so-called tungsten-based "smart alloys". In this work, we present a computational approach that uses first-principles DFT electronic structure calculations to understand the effect of the chemical environment on tungsten-based alloys. In particular, we compared the Special Quasi-random Structure (SQS) and the DFT-coupled Monte Carlo (MC-DFT) methods when investigating the short-range order and elastic properties of two equimolar WCrTaTi and WVTaTi W-HEAs, and two WCrTi and WCrY W-SAs. We found that structures after MC-DFT calculation have lower cohesive energies than SQS structures, with shorter lattice constants, and large elastic properties values. Furthermore, distinct element segregation was studied by calculating the SRO parameter and radius distribution function. The total density of states suggested that the existence of SRO could improve the stability of the structure.