# Enhancing the Elevated-Temperature Mechanical Properties of Levitation Melted NbMoTaW Refractory High-Entropy Alloys via Si Addition

## TL;DR

Adding silicon to a refractory high-entropy alloy improves its strength and hardness at high temperatures but reduces plasticity.

## Contribution

Si addition enhances mechanical properties of NbMoTaW alloys through silicide phase formation.

## Key findings

- Si addition forms (Nb,Ta)5Si3 phase, increasing strength and hardness.
- Higher Si content increases silicide volume fraction but reduces plasticity.
- Si3N4 counterfaces are optimal for evaluating RHEA wear mechanisms.

## Abstract

To enhance the mechanical properties of NbMoTaW refractory high-entropy alloys (RHEAs), Si was added at varying concentrations (x = 0, 0.25, and 0.5) via vacuum induction levitation melting (re-melted six times for homogeneity). The microstructure and mechanical properties of NbMoTaWSix (x = 0, 0.25, and 0.5) RHEAs were characterized using scanning electron microscopy (SEM), universal testing, microhardness testing, and tribological equipment. Experimental results manifested that Si addition induces the formation of the (Nb,Ta)5Si3 phase, and the volume fraction of the silicide phase increases with higher Si content, which significantly improves the alloy’s strength and hardness but deteriorates its plasticity. Enhanced wear resistance with Si addition is attributed to improved hardness and oxidation resistance. Tribological tests confirm that Si3N4 counterfaces are optimal for evaluating RHEA wear mechanisms. This work can provide guidance for the fabrication of RHEAs with excellent performance.