Science Advances

Supplementary Materials

This PDF file includes:

  • fig. S1. Measurement repeatability of COF.
  • fig. S2. Measurement results of wear rates.
  • fig. S3. Surface profiles and morphology of the CG sample under low-load single sliding.
  • fig. S4. Effect of Ag addition on COF reduction—Measurement results in pure Cu samples.
  • fig. S5. Counter surface analysis.
  • fig. S6. COF measurement on the NG, GNG, and CG samples subsequently using exactly the same contact surface of a WC-Co ball.
  • fig. S7. Stability of the subsurface microstructure in the GNG samples against sliding.
  • fig. S8. Chemical analysis of the topmost NG surface layer.
  • fig. S9. Subsurface microstructures in the CG Cu under sliding in the steady state.
  • table S1. Surface roughness change after dry sliding for 18,000 cycles.

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