Chemical Vapor Deposition of Hard Coatings in the System Ti-B-C-N

Christina Kainz

Research output: ThesisDoctoral Thesis

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Abstract

Economic requirements of the machining industry towards higher cutting speeds with simultaneous longer tool life times ask for continuous development of the used material. The application of hard protective coatings, which can be produced via chemical vapor deposition (CVD), allows to meet these requirements. The present work aims to establish design rules for simultaneously hard and tough coatings in the Ti(B,C,N) system with optimized thermo-physical properties. Two different approaches were used to improve the hardness and toughness: (i) alloying of CVD TiN coatings with B and C and (ii) application of a multilayered coating architecture. Thus, TiN, TiB0.13N0.87, TiC0.29N0.71, and TiB0.1C0.36N0.54 single-layer coatings and TiN/TiB0.13N0.87 multilayer coatings with varying bilayer periods were compared to each other in regard of their microstructure, phase composition and (micro-)mechanical properties. The latter were evaluated using micro-mechanical bending tests on free-standing coating cantilevers. The addition of B and C as well as the application of a multilayered coating architecture significantly improves the (micro )mechanical properties in comparison to single-layer TiN. Quaternary TiB0.1C0.36N0.54 exhibits the highest hardness and fracture stress among the tested coatings. The TiN/TiB0.13N0.87 multilayer with the highest number of individual layers turned out to be the toughest material in this study. Knowledge of the behavior of the coating at the actual service temperature allows to predict its performance during application. Thus, the thermo-physical properties CVD TiN, TiB2, and TiBxNy coatings with varying B contents were investigated using high-energy X-ray diffraction up to 1000 °C at a synchrotron radiation facility. Within the investigated coatings, the mean thermal expansion coefficient decreases as the B content increased, which results in a lower tendency for detrimental thermal crack formation. The thermal conductivity of the coatings decreases as well with increasing B content, which results in a better ability to protect the substrate from overheating. The deposition of CVD TiCxN1-x coatings is commonly realized using CH4 in the high temperature or CH3CN in the moderate temperature process. Within this thesis, the feasibility of using C2H6 as a C feeding source was investigated, allowing both, a reduction of the energy consumption during deposition and the possibility to adjust the C content over the whole compositional range. Five coatings with C/(C+N) ratios of 0 to 0.8 were deposited using this method and were compared regarding their microstructure, (micro )mechanical properties, and thermal conductivity. It turned out that a moderate to high C content is favorable in terms of hardness, toughness and thermal conductivity.
Translated title of the contributionChemische Gasphasenabscheidung von Hartstoffschichten im System Ti-B-C-N
Original languageEnglish
QualificationDr.mont.
Awarding Institution
  • Montanuniversität
Supervisors/Advisors
  • Mitterer, Christian, Supervisor (internal)
  • Mayrhofer, Paul Heinz, Assessor B (external)
  • Keckes, Jozef, Assessor A (internal)
Publication statusPublished - 2020

Bibliographical note

embargoed until null

Keywords

  • Hard coatings
  • Chemical vapor deposition
  • Thermo-physical properties
  • Mechanical properties
  • Cutting tools

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