Wear-life evaluation of CrN-coated steels using acoustic emission signals

This paper will present the results of single-pass scratch tests and repeated sliding tests to determine the critical load and the wear life of CrN-coated steels. Sliding tests with a diamond cone and a coated steel disc were performed under dry sliding conditions, as were the scratch tests. The test specimens were 0.2% plain carbon steels. The coefficients of friction (COF) and the acoustic emission (AE) signals were measured to determine the number of cycles to failure. From the tests it was found that the first spalling of CrN film was detected by AE signals in the early stage of coating failures, and overall failures by friction signals. Therefore, the conservative design for coating-life should be done using the results of AE signals. Using the ratio of sliding normal load/critical scratch load (the percent contact load) the cycles to failure were measured to predict the wear-life of CrN film. On the wear-life diagram the percent contact loads and the cycles to failure show a good linear relationship on the log coordinates. As the load percentage is decreased, the diagram shows that the wear-limits, at which the coated steels survive more than 3000 cycles, are approximately 4–5% of the critical scratch loads.