In Situ Crystalline‐Amorphous Composite Oxide Structure Suppressing Thermal Wear Instability for Refractory Multi‐Principal Element Alloy

ABSTRACT Refractory multi‐principal element alloys (RMPEAs) are attractive for elevated‐temperature tribology, yet many exhibit pronounced wear‐resistance degradation from ambient to medium temperatures (approximately 25°C–500°C). Conventional approaches typically rely on temperature‐specific, in situ tribo‐oxide formation, which limits the improvement to narrow operating windows. Here we demonstrate an oxygen‐induced amorphization strategy in NbMoWTaTi that produces a mechanically robust composite oxide tribo‐layer and suppresses medium‐temperature wear degradation. Oxygen incorporation into the chemically short‐range ordered NbMoWTaTi matrix promotes uniformly dispersed Ti─O clusters, leading to local lattice instability and spatially uniform amorphization. During sliding at 500°C–650°C, this process generates a composite oxide tribo‐layer comprising an amorphous matrix containing ultrafine WO 3 nanocrystals (∼5 nm), which exhibits high hardness and stiffness and supports ultra‐low wear (on the order of 10 −7 mm 3 ·N −1 ·m −1 ). In addition, pre‐fabrication of a comparable composite oxide layer reduces the wear rate by one to two orders of magnitude from 25°C to 400°C relative to the untreated alloy. These results establish oxygen‐induced amorphization as a design strategy for forming stable, high‐strength oxide tribo‐layers and achieving enhanced wear resistance across a broad service‐temperature range.