Effect of Aluminum Addition on Microstructure, Mechanical Properties, and Wear Behavior of MoNbTiV Refractory High-Entropy Alloys

The present work examines how varying aluminum content influences the structure, strength, and wear response of Al_XMoNbTiV refractory high-entropy alloys (HEAs) (x = 0, 0.5, and 1). X-ray diffraction confirms that all three compositions retain a body-centered cubic solid-solution matrix, while the lattice constant contracts slightly from 3.26 Å for the base alloy to 3.251 Å when Al reaches one atomic ratio. Al addition also refines the dendritic solidification pattern and promotes more uniform elemental distribution. Mechanical tests reveal a pronounced rise in yield strength, increasing from about 902 MPa in the Al-free alloy to roughly 1.59 GPa at x = 1, but this strengthening is accompanied by a reduction in compressive strain at fracture from nearly 40% to about 11%. Hardness follows a similar upward trend with Al addition. Dry-sliding wear experiments demonstrate that the alloys containing Al show more than a 30% decrease in wear rate relative to MoNbTiV. This result is attributed to higher hardness, microstructural refinement, and the formation of stable surface oxides during sliding. These outcomes highlight the potential of carefully tuned Al additions to produce lightweight, oxidation-resistant refractory HEAs with a favorable balance of mechanical performance and surface durability for demanding high-temperature applications.