Ultra-low wear in Ag-doped Mo matrix coating enabled by the synergy of designed and tribo-induced heterostructures

Multiscale heterostructure engineering offers an effective route to mitigating tribological degradation by enabling adaptive stress modulation and tribological characterization. Here, MoNiAl and MoNiAlAg coatings containing dual-phase (BCC/FCC) heterostructure were fabricated on Inconel 718 alloy by using atmospheric plasma spraying (APS). Among the two coatings, the MoNiAlAg system exhibits superior tribological performance from room temperature (RT) to 600°C, achieving a low friction coefficient of 0.24 and a negative wear rate of −1.9 × 10⁻⁵ mm³ N⁻¹ m⁻¹ at 600°C. Multiscale characterization reveals that this performance originates from the synergy between the pre-designed heterostructure and the tribo-induced amorphous-nanocrystalline structure. Specially, Ag incorporation promotes strain delocalization via hetero-deformation-induced (HDI) stress, while temperature-driven texture evolution in the Ag phase further enhances the load-bearing capacity of the coating. Molecular dynamics simulations further corroborate the existence of HDI stress within the dual-phase matrix. Furthermore, the negative wear rate observed at 600°C is primarily attributed to the refilling of worn surface by debris with a high coefficient of thermal expansion, combined with the volatilization of MoO₃ outside the scar, resulting in a net material accumulation within the contact region. Therefore, the negative wear rate does not refer to “zero wear” in the physical sense, but rather to ultra-low wear resulting from high-temperature oxidation and the inherent high wear resistance of coating. This work demonstrates that the heterostructure engineering represents an effective strategy for developing advanced coatings with exceptional wear resistance under extreme conditions.