The wear effect on microstructure of DLC films PECVD-deposited on Al2O3 : TiC substrates - a confocal micro-Raman study

DLC films are required to possess a high resistance to wear and provide a low coefficient of friction to protect both the head and the recording medium layer on a hard disc from the damage caused by routine read-write operation. In this study, the wear characteristic of DLC films deposited on Al2O3:TiC (70 wt.% Al2O3 + 30 wt.% TiC) substrate by plasma-enhanced chemical vapour deposition (PECVD), was studied using a pin-on-disc system. When tested against a stainless steel bearing ball (AISI-52100), the friction coefficient of Al2O3:TiC substrate was found to be reduced by approximately 74% using DLC coating with a very low wear rate under the test conditions selected. To characterize the microstructure of DLC coatings before and after wear test, confocal micro-Raman spectroscopy was used, and operated in both the point-mode and the line-mode. A change in Raman parameters of the DLC films with the wear track depth was revealed, and clearly depicted, by operating the Raman system in the line-mode. Moreover, Raman mapping of band position, band width and the band intensity of G-band and D-band can provide additional information about the changes in the film microstructure; especially over a large area. Graphitization was observed in the wear track region, which results mainly from the release of hydrogen in the DLC, caused by wear during testing. (C) 1999 Elsevier Science S.A. All rights reserved.