LAUSR

Diamond‐like carbon (DLC) coatings were indented 3000 to 15 000 times cyclically using a Si3N4 sphere having a diameter of 10 mm under a normal load of approximately 107 N. DLC coatings were prepared by unbalanced magnetron (UBM) sputtering under substrate bias voltage of −200 on a heat‐treated and polished JIS SCM 415 substrates. SEM images and the energy dispersive X‐ray spectrometry (EDX) results of the indented impressions showed that a Cr/C layer or substrate surface partially revealed on the impressions. In order to estimate structural alterations in DLC coatings after cyclic indentations, Raman spectroscopy were performed on the impressions. Relationships between Raman parameters such as the intensity ratio I(D)/I(G) of the disorder peak around 1350 cm−1 and the graphitic peak around 1580 cm−1 and full width of half maximum of the G peak (FWHM(G)) were estimated with the Raman spectroscopy on the impressions. Enclosed area by maximum and minimum of I(D)/I(G) and FWHM(G) was defined as “Safety Zone” in this paper, and it can be used to determine integrity of DLC coatings.