Synthesis and characterization of Ta-DLC coatings over CoCrMo alloy
Date
2021-12-08
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
Type
Thesis
Degree Level
Masters
Abstract
Diamond-Like Carbon (DLC) coatings have attracted a lot of attention as a viable solution to improve the lifespan of artificial joints due to its excellent mechanical and tribological properties, but their use is limited owing to their high internal stresses, which induces weak adhesion and early delamination of the coatings. Metal doping has been widely researched to enhance the adhesion of DLC, but limited research has been done on Tantalum (Ta) doping and its effect on the structural, chemical, mechanical and tribological properties of DLC coatings.
In the present thesis work, Ta doped DLC (Ta-DLC) coatings were prepared on CoCrMo alloy and Si (100) wafers using the direct current (DC) magnetron sputtering technique. Ta doping concentration was varied in the DLC matrix by altering the DC power to Ta target from 6 W to 12 W. The structure of the deposited coatings was characterized using X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). Rockwell C indentation, nanoindentation, optical profilometry, and pin-on-disc wear test were used to evaluate the mechanical and tribological properties of the coatings. Chemical characterization has showed that the Ta is present as Ta carbide (TaC) in the DLC matrix which was found to increase with increase of Ta target power. The internal stress is reduced significantly (approximately 5 times lower with low doping) by Ta doping, and thus the adhesion of the coatings is improved. Nano-indentation showed an initial increase in hardness to a maximum value of 22.2 GPa at an 8 W Ta target power and then decreased to 8.5 GPa due to the increase of TaC in the coating. Additionally, Ta doping into DLC has significantly reduced the wear rate of the polymer counterpart compared to the uncoated substrate and undoped DLC thin films. A lower coefficient of friction of 0.16 has been achieved at 8 W Ta target power which is lower than the undoped DLC coatings, showing that appropriate amounts of Ta doping can noticeably enhance the mechanical and tribological properties of DLC coatings.
Description
Keywords
DLC, Ta-DLC, Doping, interlayer, Diamond like carbon, Tantalum, internal stress, adhesion, TaC, Tantalum carbide
Citation
Degree
Master of Science (M.Sc.)
Department
Mechanical Engineering
Program
Mechanical Engineering