Gradual degeneration of liquid superlubricity: Transition from superlubricity to ordinary lubrication, and lubrication failure

The step-by-step evolution of the friction coefficient and substrate damage during the superlubricity degeneration of Si3N4/glass pair lubricated with H3PO4 solution was investigated. The experimental results indicate that the degeneration process experiences two stages after superlubricity failure. The superlubricity state initially degenerates to the ordinary lubrication state, gradually destabilizes, and eventually fails. Further analysis demonstrates that superlubricity degeneration is mainly attributed to serious substrate damage; however, the subsequent lubrication failure is mainly caused by the insufficient amount of lubricant. Moreover, load, not speed, plays a pivotal role in the wear behavior of substrate surface and further affects the superlubricity stability. The results may reveal the degeneration mechanism of liquid superlubricity and optimize the operation and design of superlubricant systems.