Gradient-grained L1₂-strengthened CoCrNi-based alloy enabling self-adaptive tribolayer formation for exceptional wear resistance

Achieving exceptional wear resistance in precipitation-strengthened alloys remains a critical challenge for structural applications in extreme environments. However, these alloys commonly suffer from unstable tribolayer formation and subsurface cracking during sliding, leading to rapid material degradation and limited wear lifetime. Here, we present a design strategy that integrates a controlled gradient grain structure into an L1₂-strengthened CoCrNi₂(Al_0.2Nb_0.2) alloy to enable in situ formation of self-protective tribolayers during dry sliding. Surface mechanical attrition treatment (SMAT) produces a continuous grain-size gradient while preserving a uniform dispersion of nanoscale L1₂ precipitates. During sliding against a Si₃N₄ counterface at room temperature (RT), a ∼135 nm amorphous–nanocrystalline composite layer develops, consisting of (Ni, Co)-rich nanocrystals embedded within a (Cr, Al, Nb)-rich amorphous oxide matrix. Cooperative deformation between amorphous and crystalline regions suppresses strain localization and crack propagation, yielding a low wear rate. At 600 °C, severe plastic deformation and accelerated oxidation produce a ∼1.1 μm laminated tribolayer composed of a compact (Co, Ni)-rich outer oxide and a (Cr, Al, Nb)-rich inner oxide. This adaptive near-surface structure, exhibiting high strength (∼10.2 GPa) and appreciable strain hardening, reduces friction and wear by nearly an order of magnitude. These findings demonstrate that synergistic control of gradient microstructure and nanoscale precipitation enables self-adaptive tribological behavior, offering a pathway toward strong, ductile, and ultra–wear-resistant alloys for extreme environments.