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On the growth, orientation and hardness of chemical vapor deposited Ti(C,N)
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.ORCID iD: 0000-0002-2361-959X
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
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Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
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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.

Place, publisher, year, edition, pages
2018. Vol. 645, p. 19-26
Keyword [en]
CVD, Ti(C, N), Hard coating, Thermodynamic modelling
National Category
Materials Chemistry
Research subject
Chemistry with specialization in Inorganic Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-334644DOI: 10.1016/j.tsf.2017.10.037ISI: 000418305200004OAI: oai:DiVA.org:uu-334644DiVA, id: diva2:1160228
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
In thesis
1. Cutting Edge Titanium-based CVD Hard Coatings
Open this publication in new window or tab >>Cutting Edge Titanium-based CVD Hard Coatings
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
Keyword
CVD, Hard coatings, Ti(C, N), TiN
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-335907 (URN)978-91-513-0184-6 (ISBN)
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

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