In Situ Formation of a Honeycomb-Like Dual-Amorphous Oxide Tribolayer via Tungsten Segregation for Exceptional Cryogenic Wear Resistance in a NbMoTaW Film

While tribochemical reactions can form a robust protective oxide surface, the oxide's limited deformability can lead to brittle cracking and thereby accelerates wear. To overcome this limitation, we developed a strategy to in situ form a deformable, honeycomb-like dual-amorphous oxide tribolayer during sliding at 77 K. This nanostructure is achieved in a NbMoTaW compositionally complex alloy film by leveraging preferential tungsten (W) segregation and heterogeneous oxidation. The resulting surface oxide features a W-depleted amorphous "core" and a W-rich amorphous "skeleton". Unlike the brittle amorphous-nanocrystalline composite tribolayer formed at room temperature, this high-strength (∼8.4 GPa yield strength) and deformable (25% homogeneous strain) dual-amorphous layer endows the NbMoTaW alloy with exceptional cryogenic wear resistance. The measured wear rate of 1.43 × 10^-6 mm³/N·m is one order of magnitude lower than that at room temperature. This work provides a design strategy for ultra-wear-resistant alloys for extreme cryogenic environments.