Session 01: DLC coatings OA 01 P2009-245 evaluation of adhesion strength and wear resistance of DLC films

Diamond-like carbon (DLC) coatings have many outstanding properties such as low friction, high wear resistance and corrosion resistance. Therefore, DLC coatings have been applied in various fields in recent years, such as cutting tools, dies, sliding parts, automotive engine parts and biomedical parts. Although the scratch test and the Rockwell test are commonly used today to evaluate the adhesion strength of DLC coatings, these techniques are insufficient under actual sliding conditions. A few papers have reported methods for evaluating the adhesion strength and wear resistance of DLC coatings under repeated sliding conditions. In this study, a sliding test in which the load was continuously increased was conducted to evaluate the adhesion strength and wear resistance of DLC coatings under practical sliding conditions. The substrate disk was made of steel (AISI 52100) with a hardness of 60 HRC and polished to a surface roughness of Ra 0.01μm. An alumina (Al₂O₃) ball held in a jig to prevent it from rotating was pressed against the toric sliding surface of the rotating disk coated with the DLC coating. Three types of DLC coatings formed by different processes were evaluated: a hydrogen-free amorphous carbon (a-C, formed by unbalanced magnetron sputtering), a hydrogen-containing amorphous carbon (a-C:H, formed by RF plasma-enhanced CVD), and a hydrogen-free tetrahedral amorphous carbon (ta-C, formed by a filtered vacuum arc). The friction coefficient and the acoustic emission signal of the DLC coatings were simultaneously measured in the sliding test under a continuously increasing load and the condition of the sliding track was observed. It was found that the a-C:H coating showed damage with clear, large fragmentation, the a-C coating showed damage due to wear, and the ta-C coating showed damage with fine fragmentation. Different damage modes were clearly seen according to the different characteristics of the DLC coatings. The test results and observations are described in detail.