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Deposition and tribomechanical properties of diamond-like carbon coatings
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Rodriguez, Bruno (2022) Deposition and tribomechanical properties of diamond-like carbon coatings. PhD thesis, University of Warwick.
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Official URL: http://webcat.warwick.ac.uk/record=b3878456~S15
Abstract
Diamond-like carbon (DLC) coatings have been widely used to protect different components in a myriad of demanding applications due to their outstanding tribological properties. The requirements of these components have evolved on parallel to the industry, which has led to stringent demands with regards to thermal stability and tribomechanical properties at temperatures above 250 ◦C.
This thesis started by understanding the effect that the different tribological parameters had in the DLC coatings deposited using direct-current magnetron sputtering (DCMS), as well as estimating contact temperatures during the tribological testing. The resulting sp2 structural changes inside the wear track were studied through a novel approach based on Raman Spectroscopy.
Different strategies were analysed with the aim of extending the thermal stability of DLC coatings deposited using DCMS, such as Si-doping, Si-Cr co-doping or increasing bias voltage. Raman spectroscopy was used to assess the thermal stability, with both Si-doping and high bias voltages found to have a positive impact, while the Cr-doping included in Si,Cr co-doping was found to have the opposite effect. The analysis of the sp2 structural changes inside the wear track was also undertaken for these DLC coatings and the contact temperature achieved at the end of the tribological testing was estimated experimentally.
With the aim of increasing the thermal stability and tribological properties beyond that obtained using Si-doping, an alternative technique - high power impulse magnetron sputtering (HiPIMS)- was employed. The process parameters were mapped to understand their effect in the DLC coatings properties, achieving a two-fold increase in hardness. These DLC coatings were found to increase the thermal stability from those in the previous chapter by - at least- 150 ◦C, while the C-C/C-H sp3 fraction increased by 10 % to values above 30 %. The specific wear rate was found to improve, by four orders of magnitude, when compared with two commercially available DLC coatings, D-iC and
G-iC, and other DLC coating in this thesis deposited using DCMS.
In the search for DLC coatings with an even larger thermal stability, further Si-doped DLC coatings- deposited using HiPIMS- were analysed. Si-doped DLC (3.3 at. %) coatings increased the thermal stability by 100 ◦C, moving the thermal stability threshold of these coatings even further. High temperature nanoindentation tests, combined with x-ray photoelecton spectroscopy (XPS), showed that the mechanical properties were not defined by the C-C/C-H sp3, but by the sp2 structural changes. The undoped DLC coating was also employed on WC-Co drills and found to outperform the uncoated drill due to the significant reduction in Al-10 % Si adhesion.
Item Type: | Thesis (PhD) | ||||
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Subjects: | T Technology > TA Engineering (General). Civil engineering (General) T Technology > TJ Mechanical engineering and machinery |
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Library of Congress Subject Headings (LCSH): | Coatings, Coating processes, Amorphous substances, Tribology, Carbon | ||||
Official Date: | 19 January 2022 | ||||
Dates: |
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Institution: | University of Warwick | ||||
Theses Department: | Warwick Manufacturing Group | ||||
Thesis Type: | PhD | ||||
Publication Status: | Unpublished | ||||
Supervisor(s)/Advisor: | Schiller, Tara ; Proprentner, Daniela ; Navabpour, Parnia | ||||
Extent: | xxi, 144 pages : illustrations, charts | ||||
Language: | eng |
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