Reactive sputtering of NbCx-based nanocomposite coatings: an up-scaling study
2014 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 253, 100-108 p.Article in journal (Refereed) Published
Nanocomposite Nb-C coatings, with a C/Nb ratio of 0.93 - 1.59, have been deposited by reactive sputtering in a commercial sputtering system at deposition rates of up to 200 nm/min. The coatings are compared to non-reactively sputtered Nb-C in lab-scale equipment at deposition rates two orders of magnitude lower. X-ray diffraction, X-ray photoelectron spectroscopy, and electron microscopy are used to conclude that all coatings consist of nanocrystalline NbCx grains (nc-NbCx) embedded in a matrix of amorphous C (a-C). The coating performance was evaluated in terms of their mechanical, tribological, and electrical properties. The chemical stability of the coatings was evaluated by exposure to a flowing mixture of corrosive gases. It is found that the coatings have comparable microstructure and performance to the coatings deposited by non-reactive sputtering. The high deposition rate and presence of different C-radicals on the coating surface during film growth for the reactively sputtered coatings is believed to result in a smaller NbCx grain size compared to the non-reactively sputtered coatings (reactive process: 10 – 3 nm, non-reactive process: ~75 – 3 nm). This difference results in a thinner a-C matrix of about 0.2 nm, which is not varying with C content for the reactively sputtered coatings. The thinner a-C matrix is reflected in coating properties, with a higher conductivity and slightly higher hardness. The coating richest in C content (C/Nb ratio 1.59) shows the lowest friction (0.23), wear rate (0.17x10-6 mm3/mN), and contact resistance before (11 mΩ at 10 N) and after (30 mΩ at 10 N) the chemical stability test. These results imply that nc-NbCx/a-C coatings of this composition are a good candidate for electrical contact applications, and that up-scaling of the process is achievable.
Place, publisher, year, edition, pages
2014. Vol. 253, 100-108 p.
thin film, carbide, electrical contacts, contact resistance, friction
Research subject Chemistry with specialization in Materials Chemistry
IdentifiersURN: urn:nbn:se:uu:diva-219028DOI: 10.1016/j.surfcoat.2014.05.021ISI: 000339150200014OAI: oai:DiVA.org:uu-219028DiVA: diva2:698056