A Different Perspective on the Solid Lubrication Performance of Black Phosphorus: Friend or Foe?

Black phosphorus (BP), a promising 2D material with exceptional electronic and optical properties, has shown remarkable potential in tribology as an additive in liquid lubrication and a composite in solid lubrication. However, its potential as the standalone solid lubricant is still at its early stage. This study evaluates BP's solid lubrication performance as deposited coating (by drop casting) on a variety of metallic substrates (polished AISI 52 100 steel, aluminum, copper, and iron) under different contact pressures using a ball‐on‐disc linear‐reciprocating test machine in dry conditions. The results demonstrate that BP does not systematically reduce friction and wear. Depending on the contact pressure and the characteristic of the substrate material (particularly surface roughness), its friction and wear behavior vary a great deal. The best results observed are a 33% reduction in friction with increased surface roughness on iron and a 23% reduction in wear on aluminum. While no general trend is observed for contact pressure effects, increased substrate roughness proves beneficial, enhancing lubricant retention and exploiting BP's low interlayer shear mechanism. Therefore, this study demonstrates that while promising, BP's solid lubrication performance is not exceptional. It also highlights the importance of optimizing test conditions and materials for enhanced lubrication.