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Cutting Edge Titanium-based CVD Hard Coatings
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Modern tools for metal cutting applications, such as turning or milling, are typically improved with a thin protective coating. Despite being only a few microns thick, the coating can increase the lifetime of the tool by more than 100 times compared to an uncoated tool. Two different types of techniques are normally used to deposit the coatings, i.e. chemical vapor deposition (CVD) or physical vapor deposition (PVD). A CVD coated tool often includes several different layers. TiN-Ti(C,N)-Al2O3-TiN is a common combination. The research in this thesis has focused on deposition, characterization, and optimization of TiN and Ti(C,N) layers. CVD has been used to deposit all coatings studied in this thesis. They were characterized with a variety of techniques such as: X-ray diffraction, electron microscopy and X-ray photoelectron spectroscopy.

TiN was deposited on three different substrates, Co, Fe and Ni. It was found that the TiN coating was strongly affected by the substrate. TiN deposited on Fe substrates resulted in a porous interface caused by substrate etching by the reaction gas mixture. CVD of TiN on Ni substrates resulted in an unwanted intermetallic phase (Ni3Ti) in addition to TiN. Etching or corrosion of the Fe substrates could be reduced by lowering the deposition temperature. In addition, the formation of (Ni3Ti) could be significantly reduced by adjusting the partial pressure of the reactant gases. This shows that CVD of TiN on cutting tools with Fe or Ni as a binder phase needs to be optimized with respect to the process parameters.

Thermodynamic calculations of the Ti(C,N) CVD process indicates that the major growth species using CH3CN, TiCl4 and H2 as precursors, was HCN and TiCl3. They were formed in the gas phase by homogeneous reactions. Furthermore, it was found that by adjusting the composition of the reaction gas mixture, the preferred orientation, morphology, and micro-structure of the Ti(C,N) coatings could be tailored. As a result, the tribological/mechanical properties of the Ti(C,N) coatings could be significantly improved. A hardness of 40 GPa, i.e. close to super hard could for instance be achieved. The origin of the mechanical improvements was attributed to a more ordered crystallographic orientation in the <111> direction as well as a high defect density close to the coating surface. In addition to the excellent mechanical properties, the Ti(C,N) coatings were also found to have a high corrosion resistance in sea water, thanks to a formation of a passivating surface layer (TiO2).

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2018. , p. 77
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1609
Keywords [en]
CVD, Hard coatings, Ti(C, N), TiN
National Category
Inorganic Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-335907ISBN: 978-91-513-0184-6 (print)OAI: oai:DiVA.org:uu-335907DiVA, id: diva2:1164135
Public defence
2018-02-02, Polhemssalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2018-01-12 Created: 2017-12-10 Last updated: 2018-03-07
List of papers
1. Chemical vapor deposition of TiN on transition metal substrates
Open this publication in new window or tab >>Chemical vapor deposition of TiN on transition metal substrates
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2018 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 334, p. 373-383Article in journal (Refereed) Published
Abstract [en]

The growth of chemical vapor deposited TiN from a reaction gas mixture of TiCl4, N-2 and H-2 was investigated on three different transition metal substrates: Fe, Co and Ni at deposition temperatures ranging from 850 degrees C to 950 degrees C. The interactions between the substrate metals and the gas phase were investigated using thermodynamic calculations. The TiN coatings were characterized by scanning electron microscopy, scanning transmission electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy and transmission Kikuchi diffraction. Chemical vapor deposition (CVD) of TiN on Co substrates resulted in dense, columnar coatings of single phase TiN. The activation energy for TiN deposition on Co was determined to be 90 kJ/mol. CVD of TiN on Fe substrates caused severe substrate corrosion by the formation of gaseous FeClx. Due to the substrate corrosion, the activation energy could not be determined. Furthermore, it was found that CVD of TiN on Ni substrates produced a phase mixture of TiN and Ni3Ti. Formation of Ni3Ti could be minimized by decreasing the H-2 partial pressure and increasing the N-2 partial pressure. Deposition on Ni yielded two different activation energies, 40 kJ/mol in the temperature interval 850 degrees C to 900 degrees C and 165 kJ/mol in the interval 900 degrees C to 950 degrees C. This is an indication of two different types of process control, which were identified as Ni diffusion into the growing film and a gas phase processes. The results of the present study showed that CVD of TiN on a cemented carbide using Fe and Ni in the binder phase, must be optimized in order to avoid corrosion or unwanted phases. Methods to achieve this are presented in this paper.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
CVD, TiN, Alternate binder phase, Thermodynamic calculations
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-335908 (URN)10.1016/j.surfcoat.2017.11.063 (DOI)000423894700045 ()
Funder
Swedish Foundation for Strategic Research , RMA15-0048
Available from: 2017-12-10 Created: 2017-12-10 Last updated: 2018-04-04Bibliographically approved
2. Texture formation in chemical vapor deposition of Ti(C,N)
Open this publication in new window or tab >>Texture formation in chemical vapor deposition of Ti(C,N)
(English)Manuscript (preprint) (Other academic)
Keywords
Growth model, Titanium compounds, Chemical vapor deposition process, X-ray diffraction
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-335894 (URN)
Funder
Swedish Foundation for Strategic Research , RMA15-0048Swedish Foundation for Strategic Research , RIF14-0053Swedish Research Council, C0514401
Available from: 2017-12-09 Created: 2017-12-09 Last updated: 2017-12-10
3. On the growth, orientation and hardness of chemical vapor deposited Ti(C,N)
Open this publication in new window or tab >>On the growth, orientation and hardness of chemical vapor deposited Ti(C,N)
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2018 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 645, p. 19-26Article in journal (Refereed) Published
Abstract [en]

Chemical vapor deposition (CVD) of Ti(C,N) from a reaction gas mixture of TiCl4, CH3CN, H2 and N2 was investigated with respect to gas phase composition and kinetics. The gas phase composition was modelled by thermodynamic calculations and the growth rate of the CVD process was measured when replacing H2 for N2 while the sum of partial pressures H2+N2 was kept constant. The N2/H2 molar ratio was varied from 0 to 19. Single crystal c-sapphire was used as substrates. It was found that low molar ratios (N2/H2 molar ratio below 0.6) lead to an increased Ti(C,N) growth rate with up to 22%, compared to deposition without added N2. The mechanism responsible for the increased growth rate was attributed to the formation and increased gas phase concentration of one major growth species, HCN, in the gas phase. The texture of the Ti(C,N) films were also studied. ⟨211⟩ textured layers were deposited at N2/H2 molar ratios below 9. At higher molar ratios, ⟨111⟩ oriented Ti(C,N) layers were deposited and the grain size increased considerably. The films deposited at a N2/H2 ratio above 9 exhibited superior hardness, reaching 37GPa. The increased hardness is attributed to an almost epitaxial orientation between the layer and the substrate. The absence of grain twinning in the ⟨111⟩ oriented layer also contributed to the increased hardness.The Ti(C,N) layers were characterized by elastic recoil detection analysis, X-ray photo electron spectroscopy, scanning electron microscopy, X-ray diffraction and nanoindentation.

Keywords
CVD, Ti(C, N), Hard coating, Thermodynamic modelling
National Category
Materials Chemistry
Research subject
Chemistry with specialization in Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-334644 (URN)10.1016/j.tsf.2017.10.037 (DOI)000418305200004 ()
Funder
Swedish Foundation for Strategic Research , RMA15-0048Swedish Foundation for Strategic Research , RIF14-0053Swedish Research Council, C0514401
Available from: 2017-11-24 Created: 2017-11-24 Last updated: 2018-01-25Bibliographically approved
4. Deformation mechanism of highly oriented Ti(C,N) coatings
Open this publication in new window or tab >>Deformation mechanism of highly oriented Ti(C,N) coatings
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(English)Manuscript (preprint) (Other academic)
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-335906 (URN)
Funder
Swedish Foundation for Strategic Research , RMA15-0048
Available from: 2017-12-10 Created: 2017-12-10 Last updated: 2017-12-10
5. Tribological properties of highly oriented Ti(C,N) deposited by chemical vapor deposition
Open this publication in new window or tab >>Tribological properties of highly oriented Ti(C,N) deposited by chemical vapor deposition
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2018 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 119, p. 593-599Article in journal (Refereed) Published
Abstract [en]

Two Ti(C,N) coatings were tested by means of micro abrasion and scratch testing. The coatings differed in grain size, orientation (<111> and <111>, <311> and <211> respectively) and hardness (36 GPa and 23 GPa respectively). The <111> oriented coating had a 20% higher wear resistance compared to the reference coating when abraded with 1 pm diamonds. When abraded with 6 pm diamonds the abrasion resistance of the reference coating was superior compared to the <111> oriented coating by 36%. Furthermore, it was found that the <111> oriented coating had 35% better adhesion compared to the reference. The improved mechanical properties of the <111> oriented coating was attributed to a high degree of orientation and the higher hardness.

National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-335909 (URN)10.1016/j.triboint.2017.11.040 (DOI)000424960500056 ()
Funder
Swedish Foundation for Strategic Research , RMA15-0048
Available from: 2017-12-10 Created: 2017-12-10 Last updated: 2018-04-06Bibliographically approved
6. Corrosion properties of CVD grown Ti(C,N) coatings in artificial seawater environment
Open this publication in new window or tab >>Corrosion properties of CVD grown Ti(C,N) coatings in artificial seawater environment
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(English)Manuscript (preprint) (Other academic)
Keywords
Corrosion, Ti(C, N), CVD, XPS
National Category
Materials Chemistry
Research subject
Chemistry with specialization in Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-335893 (URN)
Funder
Swedish Foundation for Strategic Research , RMA15-0048
Available from: 2017-12-09 Created: 2017-12-09 Last updated: 2017-12-10

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