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Improved adhesion of carbon nitride coatings on steel substrates using metal HiPIMS pretreatments
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.ORCID iD: 0000-0002-4898-5115
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.ORCID iD: 0000-0002-2837-3656
2016 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 302, 454-462 p.Article in journal (Refereed) Published
Abstract [en]

We investigate the effect of low-temperature metal pretreatments in order to improve the adhesion of CNx coatings on steel substrates, which is crucial for tribological applications. The substrate pretreatments were conducted using five different metal targets: Ti, Zr, Al, Cr, and W, operated in high power impulse magnetron sputtering mode, known to produce significant ionization of the sputtered material flux. The CNx adhesion, as assessed by Rockwell C tests, did not improve upon Ti and Zr pretreatments. This is primarily ascribed to the fact that no interlayer was formed owing to severe re-sputtering due to high fluxes of doubly-ionized metal species in the plasma. A slight improvement in adhesion was observed in the case an Al pretreatment was carried out, while the best results were obtained using Cr and W. Here, 30-s-long pretreatments were sufficient to clean the steel surface and form a metallic interlayer between substrate and coating. Transmission electron microscopy in combination with energy dispersive X-ray spectroscopy revealed that Al, Cr, and W created intermixing zones at the interlayer/substrate and the interlayer/CNx interfaces. The steel surfaces, pretreated using Cr or W, showed the highest work of adhesion with W-adh(Cr) = 1.77 J/m(2) and W-adh(W) = 1.66 J/m(2), respectively. (C) 2016 Elsevier B.V. All rights reserved.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE SA , 2016. Vol. 302, 454-462 p.
Keyword [en]
Adhesion; Steel substrate; Carbon nitride; Coating; HiPIMS; Pretreatment
National Category
Manufacturing, Surface and Joining Technology
Identifiers
URN: urn:nbn:se:liu:diva-131494DOI: 10.1016/j.surfcoat.2016.06.048ISI: 000381838400051OAI: oai:DiVA.org:liu-131494DiVA: diva2:974474
Note

Funding Agencies|VINN Excellence Center Functional Nanoscale Materials (FunMat) [2005-02666]; Swedish Foundation for Strategic Research [RMA11-0029]; Carl Trygger Foundation for Scientific Research [CTS 14:431]

Available from: 2016-09-26 Created: 2016-09-23 Last updated: 2017-11-21
In thesis
1. Low-friction and wear-resistant carbon nitride coatings for bearing components grown by magnetron sputtering
Open this publication in new window or tab >>Low-friction and wear-resistant carbon nitride coatings for bearing components grown by magnetron sputtering
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The scope of this thesis is the investigation of magnetron sputtered carbon nitride coatings suitable for roller bearing components. The research field of tribology of bearings focuses on minimizing friction between components by improving the lubricants. The development of lubricants is, however, expensive and involves environmentally deleterious chemical byproducts. A solution to avoid such harmful conditions, reduce the processing cost, and more importantly, minimize the friction, is to apply a low-friction and wear-resistant coating on the surface of the bearing. The deposition of such coatings on components can substantially increase their lifetime, reduce the maintenance costs, and eventually increase the reliability of the machinery.

Carbon nitride (CNx) coatings have high resiliency and can withstand the demanding conditions of bearing operation. The morphology of CNx coatings is highly affected by applying a negative substrate bias voltage. At high bias (100-120 V ), the coatings become denser and more homogeneous with decreased porosity, resulting in more wear-resistant materials. I also found that the duty cycle of the applied bias affects the layer morphology. Less homogeneous films are produced using lower duty cycles (i.e., in high power impulse magnetron sputtering, HiPIMS) for a specific value of bias voltage. Thus, changing bias voltage, we can manipulate the structure of CNx and design layers, depending on the requirements of the bearing application.

My results show that denser films yield higher hardness and wear-resistance, but also higher compressive stress, which is a disadvantage for the coating-substrate adhesion. In order to obtain improved adhesion on bearing steel, we developed an in-situ surface treatment, prior to the CNx deposition, which also surpasses the limitations set by the properties of each material. The steel substrates are successfully pretreated using W or Cr ions originating from a HiPIMS source. Plasma ions are accelerated to the substrates with energies of 900 eV , due to the application of a synchronized high bias voltage, which clean effectively the substrate surface from residual contaminants and strengthen the interfacial bonding.

CNx-coated rollers are tested in rolling operation and show the absence of run-in period in all lubrication regimes. This is a big advantage for applications which rotate under boundary lubrication (BL). The coated rollers yield friction coefficients in the range of 0:020 and 0:025 in elastohydrodynamic (EHDL) and hydrodynamic (HDL) lubrication regimes, being lower than the friction coefficients of 0:026-0:052, exhibited by the uncoated rollers. Here, friction decreases steadily with increasing number of cycles, due to the presence of CNx in the contact. In BL, CNx-coated rollers present an increased friction coefficient of 0:052, but the wear is much lower than in the case of uncoated rollers. All rollers are covered with CNx in the wear tracks after the tests, avoiding failures and presenting low abrasive wear. The obtained tribological performance of the CNx-coated rollers in rolling is overall improved compared to the established operation of uncoated rollers. Thus, CNx layers can function as low-friction and wear-resistant coatings protecting the steel components in several roller bearing applications, such as in gearboxes and wheels in automotive, aerospace, marine, and turbine industry.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2016. 116 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1783
Keyword
Carbon nitride, magnetron sputtering, physical vapor deposition, coatings, bearings, rolling contact fatigue, adhesion, friction, wear, transmission electron microscopy, scanning electron microscopy, x-ray photoelectron spectroscopy, coatings tribology, nanotribology
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-132154 (URN)10.3384/diss.diva-132154 (DOI)9789176857007 (ISBN)
Public defence
2016-11-18, Planck, Fysikhuset, Campus Valla, Linköping, 09:15 (English)
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Available from: 2016-10-19 Created: 2016-10-19 Last updated: 2016-12-28Bibliographically approved

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