Temperature dependent erosion and Raman analyses of arc-deposited H free thick DLC coating on Cr/CrN coated plasma nitrided steel

Abstract

Development of H and metal dopant-free single phase thick diamond like carbon (DLC) coating on metal nitride layer for automobile applications is still a challenging task due to internal stress developed during deposition of DLC films. A simple process was followed to deposit thick Cr/CrN/DLC (0.25/0.75/6 μm) coating on plasma nitrided steel using an un-filtered cathodic vacuum arc system without applying any high pulse bias voltage. In addition, the coating was deposited at room temperature and it showed very good adhesion on plasma nitrided steel surface and exhibited a very low coefficient of friction ~0.06 ± 0.005. Temperature dependent solid particle erosion tests were conducted according to ASTM-G-76-18 standards at an impinging angle of 45°. Erosion resistance of the coating is 33, 11, 7 and 6 times better than nitrided steel substrate at test temperatures of 25, 200, 300 and 400 °C, respectively. Better erosion resistance performance of a coating infers the long life of the coating on automobile components. A multi-wavelength Raman study gives a better understanding of the structural properties of DLC. So, the Raman spectra of the coating were recorded using three different laser wavelengths: 405 nm, 532 nm and 633 nm. The thermal stability of the coating was studied using temperature dependent Raman spectroscopy. The coating showed good thermal stability until a temperature of 425 °C.