Classical tribology and charge-energy evolution theory cooperate to determine nitrided ceramic coating/metal substrate interfacial friction

Who governs interfacial friction, classical tribology theory or charge-energy evolution theory? Since it was widely recognized that the origin of friction is interatomic forces, attention has gradually shifted towards the characteristics of local nanoscale interfaces. The new theory believes the charge density evolution during the friction process has more significant attributes in determining the interfacial friction. Here, we discuss the frictional failure mechanism at the ceramic/metal interface formed after the nitriding. The increase in N-doped interface friction is supported by classical tribology theory and corresponds to high interface adhesion work. On the other hand, the H-doped interface with the lowest adhesion work exhibits the highest friction. Unlike other interface systems (metallic bonding), the failure interface after H doping is an ionic bonding interface. Stronger ionic bonds are formed and broken in relative sliding, significantly increasing charge density. This emphasizes the crucial role of charge density in this process, aligning with the principles of the new theory. Nevertheless, the classical tribology theory can still be used when measuring interfacial friction of the interface with the same chemical bonds, and it may be more convincing than the new theory. Overall, these research results reveal the intrinsic origin of H/N’s influence on TiN/Ti interfacial friction and provide new insights into understanding natural failures at the nanometer level. 

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