Transition of friction properties and failure mechanisms of metal-impregnated carbon strip induced by competition between current-induced lubrication and arc erosion under varying current densities

With the increasing speed of high-speed railways, elevated current-carrying density exacerbates wear failure of metal-impregnated carbon strips in the pantograph-catenary system. This study focuses on the competitive interaction between current-induced lubrication and arc erosion, clarifying how current-carrying density regulates their wear failure mechanism transition and tribological behaviors. Experiments were conducted at 300 km/h sliding speed, 150 km sliding distance, 90 N normal load, with current-carrying densities of 0–0.4 A/mm2. Results show that the coefficient of friction and wear rate follow a V-shaped trend and reach the minimum value at 0.1 A/mm2. A secondary critical threshold appears at 0.3 A/mm2: below this threshold, current-induced lubrication dominates to reduce friction and wear; when the density exceeds approximately 0.3 A/mm2, contact resistance and arc energy surge sharply, triggering severe interfacial degradation and aggravated wear. Furthermore, microscopic analysis of the worn surfaces through scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) revealed that the interfacial oxygen content increases from 6.2% to 28.5% with increasing current-carrying density. The wear failure mechanism evolves from mechanical wear to oxidative wear, and finally to arc erosion and molten droplet sputtering at high current-carrying density. This work identifies the performance transition threshold and clarifies the coupled electro-thermal-mechanical wear mechanism, providing a theoretical basis for optimizing the safe service range of carbon strip.