Fabrication and Wear Performance of Al Matrix Composites Reinforced with Metallic and Oxidized WMoNb Medium-Entropy Alloy Powders

Aluminum matrix composites reinforced with refractory medium-entropy alloy particles are of growing interest for wear-resistant applications, yet the contribution of an oxidized core–shell reinforcement remains largely unexplored. This study investigates the fabrication and tribological performance of Al composites reinforced with WMoNb refractory medium-entropy alloy (RMEA) powder and its oxidized derivative (RMEO). Equiatomic WMoNb powder was synthesized by 150 h high-energy ball milling, forming a single-phase BCC solid solution, then oxidized at 650 °C/4 h, selectively converting Mo and Nb into Mo4O11 and NbO0.76 while W remained metallic, yielding a core–shell RMEO structure. Composites containing 2.5–10 wt.% RMEA or RMEO were fabricated by cold pressing/sintering and evaluated by dry sliding wear testing (pin-on-disc, Al2O3 counterpart). Both reinforcements reduced friction and wear loss relative to pure Al in a dose-dependent manner; RMEO outperformed RMEA at every ratio, cutting friction and wear loss by ~60% at 10 wt.% and reaching the highest hardness (132 HB) of all compositions. Worn-surface and profilometric analyses revealed a wear-mechanism shift from severe adhesive/abrasive wear in pure Al to a tribo-oxide-mediated regime in RMEO composites. These findings indicate that selective oxidation of refractory medium-entropy alloy powders is an effective strategy for enhancing the wear resistance of Al matrix composites.