Enhanced Tribological Performance of Diamond Films by Utilizing DLC and DLC-H Top Layers

High-performance diamond films are highly demanded on tool surfaces for wire-drawing and mechanical sealing applications.Herein,this work aims at enhancing the tribological performance of chemical vapor deposition diamond films in water-lubricated conditions by utilizing non-hydrogenated and hydrogenated diamond-like carbon(DLC and DLC-H)top layers.The tribological properties of bilayer micro-crystalline diamond(MCD)/DLC,MCD/DLC-H,nano-crystalline diamond(NCD)/DLC and NCD/DLC-H films are evaluated,in terms of maximal and stable coefficients of friction(COFs),C—C bonds transformation,worn surface morphology and specific wear rates.The results show that DLC or DLC-H coated on diamond layer significantly suppresses the initial maximal COF peak and the wear of counterpart ball.Moreover,severe regular arranged sp^(2) C—C bonds transformation is detected on MCD film,in comparison to NCD;while inversely,the NCD/DLC bilayer exhibits severer C—C bonds transformation effect compared with the MCD/DLC.Furthermore,the DLC-H top layer shows a larger decreasing rate of maximal COFs and wear rates of counterpart balls,compared with the DLC coating,which is due to its superior self-lubricity.Among all the tested films,the NCD/DLC-H bilayer shows an optimized tribological performance.