Fig. 2: Tribometric setup and experimental friction and wear results.

a Schematic of the experimental setup. b Coefficient of friction (μ) over the experimental duration for various humidity values. Each experiment was repeated three times for 500 cycles each at a stroke length of 1 mm, a velocity of 0.5 mm s⁻¹, and a normal force of 402 mN. For the experiments conducted at lower humidity RH (≤30%) the average of three consecutive measurements for each humidity is shown in the upper panel. The standard deviation of three measurements is marked as the semi-transparent areas. In the lower panel all measurements at the higher humidity values (37% and 45% RH) are shown (shades of orange/red: 37% RH, shades of blue: 45% RH, purple: contact immersed in deionized water). c Average steady-state CoF after running-in with the standard error of the mean as error bars, and literature values^{7,14,36,44,45} in blue as a comparison. Black circles represent the average of 100 cycles at the end of the experiment for RH ≤ 30% or the average of 20 cycles prior to rise in μ for RH > 30%. In the latter case, the steady-state high friction values are plotted in red (average of the last 100 cycles). d Wear coefficient of the graphite-coated iron plate after 500 cycles with standard error of the mean as error bars. Wear data of the counterbodies can be found in Supplementary Fig. 1.