Ultra-Fast Synthesis of High Entropy Boride Layers and Their Characterization

In this study, we used an ultra-fast boriding process to quickly and uniformly produce thick boride layers on high entropy refractory alloys consisting of W, Re, Nb, Zr, Ta, and V. Boriding is performed at 1000°C and for 1 hour. Chemical, structural, and mechanical characterization of the boride layers was carried out using relevant test methods and confirmed that W and Re-containing alloys were among the very best in terms of boride layer thickness of 40 µm and hardness. While, Nb, Ta, and V containing alloys attained thickness values of around 3 µm. Nano hardness profiles across the boride layers revealed that W and Re-containing alloys possessed exceptional hardness, i.e., around 40 GPa. In the cases of other alloys, hardness values of boride layers fell between 18.5 GPa and 8 GPa. Such significant variations in thickness and hardness highlight the need for a more systematic and predictive modeling approach that can provide critical information on the selection of constituent refractory metals in high entropy alloy systems as well as desirable boride phases with superior mechanical, thermal, and oxidative properties.