Evaluation of Adhesion and Wear Resistance of DLC Films Deposited by Various Methods

Diamond-like carbon (DLC) coatings are currently being used in a wide variety of industrial fields because of their outstanding properties, such as high hardness and low friction coefficient, among others. DLC coatings have various characteristics depending on the deposition method used. However, they have a problem regarding adhesion with the base material, which is a major factor hindering their expanded application in other fields. The adhesion of DLC coatings is generally evaluated using Rockwell indentation tests and scratch tests. These test methods induce damage in the specimen with the application of a single load. Accordingly, there is a problem of low correlation between such test results and evaluations of the adhesion of coatings on actual components that undergo repeated sliding cycles. With the aim of resolving that problem, this study evaluated the damage condition of three types of DLC coatings having different physical properties using newly devised cyclic sliding test methods involving the application of a continuously increasing load. The evaluation results obtained with these new methods differed from the results of Rockwell tests and scratch tests. These new test methods are more able to reproduce the damage done to DLC coatings in actual sliding cycles. This paper describes the test procedures and the evaluation results obtained.