Macroscale Superlubricity on High‐Roughness Engineering Steel Surface Through Wear Debris‐Converted Tribofilm and Carbon Nanotubes

Abstract Macroscale liquid superlubricity has profound significance for energy conservation and emission reduction. However, it suffers from low tolerance to high roughness, which seriously hinders the application in engineering friction systems. Although conventional understanding holds that wear debris accumulations increase friction and wear, the anti‐wear metal oxides (e.g., Fe 2 O 3 and Cr 2 O 3 ) in the debris from steel friction pairs are expected to form a protective oxidation film and reduce surface roughness. Here, a strategy using the synergetic effects of wear debris‐converted tribofilm and hydroxylated carbon nanotubes (CNTs) to promote the low‐wear superlubricity on high‐roughness steel surfaces ( R a ≈ 57 nm) is reported. The wear rate (4.41 × 10 −8 mm 3 Nm −1 ) is reduced by 64% while achieving a low coefficient of friction (COF ≈ 0.005). The debris is manipulated to convert into a protective oxidation film and reduce surface roughness via surface design. Then, the increase in metal hydroxides generated by tribochemical reactions allows the formation of a strengthened hydrogen bond network and the stronger adsorption of the CNTs, reducing friction and wear. This work, which turns wear debris into a “treasure”, can offer a new insight into the role of wear debris in promoting low‐wear superlubricity for highly rough engineering steel.