Microstructure, composition and properties of Cr-GLC graded coating deposited by unbalanced magnetron sputtering

Cr doped graphite-like carbon (Cr-GLC) graded coating with Cr bottom layer, Cr/C composition gradient layer and Cr-GLC top layer was deposited by unbalanced magnetron co-sputtering of pure chromium and graphite targets. The microstructure, composition and properties including adhesion strength, wear resistance of the as-fabricated Cr-GLC graded coating were investigated by TEM, XPS, scratch test and sliding friction test. Three kinds of phases are detected in the graded layer: pure Cr, a Cr/C nanocrystalline/amorphous phase and amorphous carbon. The HRTEM observation for Cr-GLC top layer with 3 at% Cr indicates that Cr-enriched clusters are embedded in an amorphous carbon matrix. Results of the investigation demonstrate that strong adhesion and stable friction coefficient of the Cr-GLC graded coating are attributed to the consecutive interface microstructure in the coating caused by the interlayer design.