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

Black phosphorous (BP), a promising 2D material with exceptional electronic andoptical properties, has shown remarkable potential in tribology as an additive inliquid lubrication and a composite in solid lubrication. However, its potential as thestandalone solid lubricant is still at its early stage. This study evaluates BP’s solidlubrication performance as deposited coating (by drop casting) on a variety ofmetallic substrates (polished AISI 52 100 steel, aluminum, copper, and iron) underdifferent contact pressures using a ball-on-disc linear-reciprocating test machine indry conditions. The results demonstrate that BP does not systematically reducefriction and wear. Depending on the contact pressure and the characteristic of thesubstrate material (particularly surface roughness), its friction and wear behaviorvary a great deal. The best results observed are a 33% reduction in friction withincreased surface roughness on iron and a 23% reduction in wear on aluminum.While no general trend is observed for contact pressure effects, increased substrateroughness proves beneficial, enhancing lubricant retention and exploiting BP’s lowinterlayer shear mechanism. Therefore, this study demonstrates that while promis-ing, BP’s solid lubrication performance is not exceptional. It also highlights theimportance of optimizing test conditions and materials for enhanced lubrication.