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TiC-based nanocomposite coatings as electrical contacts
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This Thesis concerns the advanced surface engineering of novel TiC-based nanocomposite and AgI electrical contact materials. The objective is to make industrially applicable coatings that are electrically conductive and wear-resistant, and have a low coefficient of friction. I have studied electrical contact systems consisting of a Cu substrate with a Ni diffusion barrier and loading support, and a conductive top coating. The contact systems were characterized by x-ray diffraction and photoelectron spectroscopy, analytical electron microscopy, ion beam analysis, nanoindentation, resistivity, and contact resistance measurements. Nc-TiC/a-C/SiC nanocomposite coatings consisting of nanocrystalline (nc) TiC embedded in an amorphous (a) matrix of C/SiC were deposited by magnetron sputtering with rates as high as 16 μm/h. These coatings have a contact resistance comparable with Ag at high loads (~800 N) and a resistivity of 160-770 μΩcm. The electrical properties of the contact can be improved by adding Ag to make nc-Ag/nc-TiC/a-SiC nanocomposites. It is possible to tailor the size and distribution of the Ag grains by varying the fraction of amorphous matrix, so as to achieve good conductivity in all directions in the coatings. Ti-Si-C-Ag coatings have a contact resistance that is one magnitude larger than Ag at lower loads (~1 N), and a resistivity of 77-142 μΩcm. The conductivity of the matrix phase can be increased by substituting Ge, Sn or Cu for Si, which also reduces the Ag grain growth. This yields coatings with a contact resistance twice as high as Ag at loads of 1 N, and a resistivity 274-1013 μΩcm. The application of a conductive top layer of Ag-Pd upon a Ti-Si-C-Ag:Pd coating can further reduce the contact resistance. For barrier materials against Cu interdiffusion, it is shown that conventional electroplating of Ni can be replaced with sputtering of Ni or Ti layers. This is an advantage since both contact and barrier layers can now be deposited in and by the same deposition process. For Ti-B-C coatings deposited by magnetron sputtering, I demonstrate promising electrical properties in a materials system otherwise known for its good mechanical properties. In coatings of low B concentration, the B is incorporated into the TiC phase, probably by enrichment on the TiC{111} planes. The corresponding disturbance of the cubic symmetry results in a rhombohedral TiC:B structure. Finally, it is shown that AgI coatings consisting of weakly agglomerated AgI grains function as solid lubricant on Ag contacts. In an Ag sliding electrical contact, AgI decreases the friction coefficient from ~1.2 to ~0.4. After a few hundred operations, AgI grains have deagglomerated and Ag from the underlying layer is exposed on the surface and the contact resistance decreases to < 100 μΩ.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press , 2011. , 63 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1408
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-72228ISBN: 978-91-7393-030-7 (print)OAI: oai:DiVA.org:liu-72228DiVA: diva2:458509
Public defence
2011-12-02, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2011-11-23 Created: 2011-11-23 Last updated: 2016-08-31Bibliographically approved
List of papers
1. High-rate deposition of amorphous and nanocomposite Ti-Si-C multifunctional coatings
Open this publication in new window or tab >>High-rate deposition of amorphous and nanocomposite Ti-Si-C multifunctional coatings
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2010 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 205, no 2, 299-305 p.Article in journal (Refereed) Published
Abstract [en]

Amorphous (a) and nanocomposite Ti–Si–C coatings were deposited at rates up to 16 μm/h by direct current magnetron sputtering from a Ti3SiC2 compound target, using an industrial pilot-plant system, onto high-speed steel, Si, and SiO2 substrates as well as Ni-plated Cu cylinders, kept at a temperature of 200 or 270 °C. Electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction analyses showed that TiC/a-C/a-SiC nanocomposites were formed consisting of textured TiC nanocrystallites (nc) embedded in a matrix of a-C and a-SiC. Elastic recoil detection analysis showed that coatings deposited at a target-to-substrate distance of 2 cm and an Ar pressure of 10 mTorr have a composition close to that of the Ti3SiC2 compound target, as explained by ballistic transport of the species. Increased target-to-substrate distance from 2 cm to 8 cm resulted in a higher carbon-to-titanium ratio in the coatings than for the Ti3SiC2 compound target, due to different gas-phase scattering properties between the sputtered species. The coating microstructure could be modified from nanocrystalline to predominantly amorphous by changing the pressure and target-to-substrate conditions to 4 mTorr and 2 cm, respectively. A decreased pressure from 10 mTorr to 4 or 2 mTorr at a target-to-substrate distance of 2 cm decreased the deposition rate up to a factor of ~7 as explained by resputtering and an increase in the plasma sheath thickness. The coatings exhibited electrical resistivity in the range 160–800 μΩ cm, contact resistance down to 0.8 mΩ at a contact force of 40 N, and nanoindentation hardness in the range of 6–38 GPa.

Place, publisher, year, edition, pages
Elsevier, 2010
Keyword
Nanocomposites, TiSiC coatings, pilot plant, magnetron sputtering, resistivity, electron microscopy
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-59241 (URN)10.1016/j.surfcoat.2010.06.051 (DOI)000282542300010 ()
Note
Original Publication: Jonas Lauridsen, Per Eklund, T. Joelsson, H. Ljungcrantz, Å. Öberg, E. Lewin, U. Jansson, Manfred Beckers, Hans Högberg and Lars Hultman, High-rate deposition of amorphous and nanocomposite Ti-Si-C multifunctional coatings, 2010, Surface & Coatings Technology, (205), 2, 299-305. http://dx.doi.org/10.1016/j.surfcoat.2010.06.051 Copyright: Elsevier Science B.V., Amsterdam. http://www.elsevier.com/ Available from: 2010-09-10 Created: 2010-09-10 Last updated: 2017-12-12Bibliographically approved
2. Microstructure evolution of Ti-Si-C-Ag nanocomposite coatings deposited by DC magnetron sputtering
Open this publication in new window or tab >>Microstructure evolution of Ti-Si-C-Ag nanocomposite coatings deposited by DC magnetron sputtering
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2010 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 58, no 20, 6592-6599 p.Article in journal (Refereed) Published
Abstract [en]

Nanocomposite coatings consisting of Ag and TiCx (x andlt; 1) crystallites in a matrix of amorphous SiC were deposited by high-rate magnetron sputtering from Ti-Si-C-Ag compound targets. Different target compositions were used to achieve coatings with a Si content of similar to 13 at.%, while varying the C/Ti ratio and Ag content. Electron microscopy, helium ion microscopy, X-ray photoelectron spectroscopy and X-ray diffraction were employed to trace Ag segregation during deposition and possible decomposition of amorphous SiC. Eutectic interaction between Ag and Si is observed, and the Ag forms threading grains which coarsen with increased coating thickness. The coatings can be tailored for conductivity horizontally or vertically by controlling the shape and distribution of the Ag precipitates. Coatings were fabricated with hardness in the range 10-18 GPa and resistivity in the range 77-142 mu Omega cm.

Place, publisher, year, edition, pages
Elsevier Science B.V., Amsterdam., 2010
Keyword
Nanocomposite, Analytical electron microscopy, Helium ion microscopy, X-ray photoelectron spectroscopy, Eutectic solidification
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-63405 (URN)10.1016/j.actamat.2010.08.018 (DOI)000284446500004 ()
Note
Original Publication: Jonas Lauridsen, Per Eklund, Jens Jensen, H Ljungcrantz, A Oberg, E Lewin, U Jansson, A Flink, H Hogberg and Lars Hultman, Microstructure evolution of Ti-Si-C-Ag nanocomposite coatings deposited by DC magnetron sputtering, 2010, ACTA MATERIALIA, (58), 20, 6592-6599. http://dx.doi.org/10.1016/j.actamat.2010.08.018 Copyright: Elsevier Science B.V., Amsterdam. http://www.elsevier.com/ Available from: 2010-12-17 Created: 2010-12-17 Last updated: 2017-12-11Bibliographically approved
3. Deposition of Ti-Si-C-Ag nanocomposite coatings as electrical contact material
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2010 (English)In: Proceedings of the 56th IEEE Holm Conference on Electrical Contacts (HOLM), IEEE , 2010, 288-294 p.Conference paper, Published paper (Other academic)
Abstract [en]

This paper is a brief review of our recent work and a follow up study on nanocomposite coatings comprising nanocrystalline TiC embedded in an amorphous SiC matrix (nc-TiC/a-SiC) with and without Ag additions applied as electrical contacts. These coating materials are deposited at very high deposition rates (>10 μm/h), to meet industrial demands of high productivity. Here we consider Ti-Si-C-Ag nanocomposite coatings with Ag content in the range of 0-22 at.% deposited in a pilot-plant or an industrial deposition system by dc magnetron sputtering from compound targets onto Si(100) and SiO2(100) substrates. The microstructure, electrical, and mechanical properties of the coatings were studied with transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, electrical contact resistance, resistivity, and nanoindentation measurements. Varying the deposition parameters bias and pressure within ranges typical of coating processing had no effect on the structure. A variation was, however, observed for the contact resistance, that was determined to be in the range 400-900 mΩ at a contact force between 1.9-2.65 N. The coatings with highest Ag content had the lowest contactresistance.

Place, publisher, year, edition, pages
IEEE, 2010
Series
Conference on Electrical Contacts (HOLM), ISSN 1062-6808 ; 56
Keyword
Nanocomposite; TiSiC coatings; Electrical contacts; Magnetron sputtering; Contact resistance; Electron microscopy
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-72224 (URN)10.1109/HOLM.2010.5619528 (DOI)978-1-4244-8174-3 (ISBN)
Conference
56th IEEE Holm Conference on Electrical Contacts, Charleston, October 4-7
Available from: 2011-11-23 Created: 2011-11-23 Last updated: 2016-08-31Bibliographically approved
4. Effects of A-elements (A = Si, Ge or Sn) on the structure and electrical contact properties of Ti-A-C-Ag nanocomposites
Open this publication in new window or tab >>Effects of A-elements (A = Si, Ge or Sn) on the structure and electrical contact properties of Ti-A-C-Ag nanocomposites
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2012 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 520, no 16, 5128-5136 p.Article in journal (Refereed) Published
Abstract [en]

Ti-A-C-Ag (A is Si, Ge or Sn) nanocomposite coatings have been deposited by dc magnetron sputtering in an ultra high vacuum chamber. Electron microscopy, energy-dispersive x-ray spectroscopy, xray photoelectron spectroscopy, and x-ray diffraction show that all coatings contain nanocrystalline TiC and Ag grains in a matrix of mainly amorphous C. A C/Ti ratio above unity yields a homogenous distribution of Ag with a reduced grain size. From a chemical point of view, the addition of Ge and Sn to the Ti-C-Ag system should increase the conductivity of the coatings since the formation of more metallic phases than Si. We demonstrate that Si can be replaced with Ge and Sn and still yield a homogeneous distribution of Ag. The incorporation of Ge and Sn to the Ti-C-Ag system results in elemental precipitation and intermetallic phases, respectively. This gives improved electrical properties compared to Ti-Si-C-Ag coatings, and a contact resistance at loads of ~1 N against an Au probe (radius of 0.7 mm) that is comparable to that of Ag.

Place, publisher, year, edition, pages
Elsevier, 2012
Keyword
Multifunctional coatings; Nanocrystalline; Electron microscopy; Contact resistance; TiC; Ag
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-72225 (URN)10.1016/j.tsf.2012.04.037 (DOI)000305719000003 ()
Available from: 2011-11-23 Created: 2011-11-23 Last updated: 2017-12-08Bibliographically approved
5. Contact resistance of Ti-Si-C-Ag and Ti-Si-C-Ag-Pd nanocomposite coatings
Open this publication in new window or tab >>Contact resistance of Ti-Si-C-Ag and Ti-Si-C-Ag-Pd nanocomposite coatings
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2012 (English)In: Journal of Electronic Materials, ISSN 0361-5235, E-ISSN 1543-186X, Vol. 41, no 3, 560-567 p.Article in journal (Refereed) Published
Abstract [en]

Ti-Si-C-Ag-Pd and Ti-Si-C-Ag nanocomposite coatings were deposited by magnetronsputtering on Cu substrates with an electroplated Ni layer. Analytical electronmicroscopy and x-ray diffraction show that the nanocomposites consist of TiC,Ag:Pd, and amorphous SiC. The contact resistance of these coatings against aspherical Au-Co surface was measured for applied contact force up 0 to 5 N. Ti-Si-CAg-Pd coatings with a Ag:Pd strike coating has ~10 times lower contact resistance atcontact forces below 1 N (~10 mΩ at ~0.1N), and ~2 times lower for contact forcesaround 5 N (<1 mΩ at 5 N), compared to the Ti-Si-C-Ag coating.

Place, publisher, year, edition, pages
Springer, 2012
Keyword
titanium carbide; nanocomposite; physical vapor deposition (PVD); contact resistance; surface roughness; silver palladium
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-63625 (URN)10.1007/s11664-011-1813-8 (DOI)000299930100022 ()
Note
Funding Agencies|European EraSME||Swedish Knowledge Foundation||Swedish Board for Innovation Systems VINN Excellence Center on Functional Nanostructured Materials (FunMat)||Available from: 2010-12-28 Created: 2010-12-28 Last updated: 2017-12-11Bibliographically approved
6. Ni and Ti diffusion barrier layers between Ti-Si-C-Ag nanocomposite coatings and Cu-based substrates
Open this publication in new window or tab >>Ni and Ti diffusion barrier layers between Ti-Si-C-Ag nanocomposite coatings and Cu-based substrates
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2012 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 206, no 8-9, 2558-2565 p.Article in journal (Refereed) Published
Abstract [en]

Sputtered Ni and Ti layers were investigated as substitutes for electroplated Ni as adiffusion barrier between Ti-Si-C and Ti-Si-C-Ag nanocomposite coatings and Cu orCuSn substrates. Samples were subjected to thermal annealing studies by exposure to400 ºC during 11 h. Dense diffusion barrier and coating hindered Cu from diffusing tothe surface. This condition was achieved for electroplated Ni in combination withmagnetron-sputtered Ti-Si-C and Ti-Si-C-Ag layers deposited at 230 ºC and 300 ºC,and sputtered Ti or Ni layers in combination with Ti-Si-C-Ag deposited at 300 ºC.

Place, publisher, year, edition, pages
Elsevier, 2012
Keyword
Titanium carbide; nanocomposite; physical vapor deposition (PVD); diffusion; barrier; annealing
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-63624 (URN)10.1016/j.surfcoat.2011.11.014 (DOI)000300458500069 ()
Note

funding agencies|The European EraSME Program||Swedish Knowledge Foundation||The Swedish Board for Innovation Systems VINN Excellence Center on Functional Nanostructured Materials (FunMat)||

Available from: 2010-12-28 Created: 2010-12-28 Last updated: 2017-12-11Bibliographically approved
7. Ti-B-C nanocomposite coatings deposited by magnetron sputtering
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Ti-B-C nanocomposite coatings with a B content of 7-16 at.%, have been deposited by magnetron sputtering from B4C, Ti, and C targets. X-ray diffraction, photoelectron spectroscopy, and electron microscopy show that the coatings consist of nanocrystalline (nc) TiC:B embedded in a matrix of amorphous (a) BCx and C. The fraction of amorphous phase scales with the Ti concentration, where the matrix predominantly consists of free C with some BCx in coatings with 8 at.% B, while the matrix  predominantly consists of BCx with some free C in coatings with 16 at.% B. Nc-TiC:B/a-BCx/a-C coatings with low amount of free C exhibit a contact resistance comparable to the contact resistance of an Ag sputtered coating at loads of ~1 N against an Au probe.

Keyword
Nanocrystalline; Electron microscopy; Contact resistance; B4C; TiC
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-72226 (URN)
Available from: 2011-11-23 Created: 2011-11-23 Last updated: 2016-08-31Bibliographically approved
8. AgI as a solid lubricant in electrical contacts
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

AgI coatings have been deposited by electroplating on Ag plated Cu coupons. Electron microscopy shows that the coatings consist of weakly agglomerated AgI grains. X-ray diffraction, differential scanning  calorimetry, thermogravimetry and mass spectrometry show that the AgI exhibits a reversible transformation from hexagonal to cubic phase at 150 °C. AgI starts to decompose at 150 °C with an accelerating rate up to the AgI melting temperature (555 °C), where a complex-bonded  hydroxide evaporates. Ag-pin-on-disk testing shows that the iodine addition to Ag decreases the friction coefficient from 1.2 to ~0.4. The contact resistance between AgI and Ag becomes less than 100 μΩ after ~500 operations as the AgI deagglomerates and Ag is exposed on the surface, and remains low during at least 10000 reciprocating operations. This makes AgI suitable as a solid lubricant in electrical contacts.

Keyword
Silver Iodide; Friction coefficient; Contact resistance; TEM; Phase transformation; DSC
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-72227 (URN)
Available from: 2011-11-23 Created: 2011-11-23 Last updated: 2016-08-31Bibliographically approved

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