|dc.description.abstract||Energy losses in moving components due to high friction and wear are one of the biggest challenges faced by industries. AISI 316L stainless steel (SS) is one of the most widely used alloyed steel for moving parts in corrosive environments. However, its poor tribological properties result in limited longevity and performance. As lubrication is not an option for food processing and biomedical devices, surface modification of the SS is usually required. Nitriding and carburizing can enhance its wear resistance but result in a high coefficient of friction (COF) and poor corrosion resistance. Coating Diamond-like carbon (DLC) films are very promising to lower its COF and increase its wear and corrosion resistance as well as biocompatibility. However, the application has been limited due to its poor adhesion to SS substrates.
The present thesis work aims to use a chromium nitride (CrN) thin film as an interlayer to enhance DLC adhesion on the SS substrate. CrN thin films with various microstructures and thicknesses were first deposited onto the SS substrate using radio frequency magnetron sputtering under different deposition conditions. DLC coatings were then deposited on the CrN interlayered SS substrates using ion beam deposition (IBD). The deposited CrN interlayers and DLC coatings were then characterized by various techniques including grazing incidence X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy, optical profilometry, nanoindentation, Rockwell C indentation, and ball-on-disc tribological testing.
The results show that the microstructure and the corresponding mechanical properties of the sputtered CrN thin films can be tailored by changing deposition parameters. CrN films deposited at 470 °C and 10 mTorr pressure had a dense, net-like structure with a hardness of 8 GPa, and significantly enhanced DLC adhesion on the steel. The interlayer, deposited with a thickness ranging from 0.4 to 2.1 µm, was found to play an important role in improving DLC adhesion. The thicker the interlayer, the better the adhesion. Furthermore, good DLC adhesion on the steel was achieved by doping DLC with nitrogen at a thinner CrN interlayer of 1.1 µm because of the reduced intrinsic stress in nitrogen doped DLC coatings. Finally, wear testing results showed that DLC coating can decrease COF and wear rate of the steel when sliding with AISI 302 ball.||