Design of CVD Coatings for Cutting Tools

Christoph Czettl

Research output: ThesisDoctoral Thesis

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Abstract

The trend of higher productivity and cost efficiency in the metal cutting industry leads to increased demands of tools, regarding higher feed rates and cutting velocity in combination with higher reliability. Therefore, the wear resistance, thermal stability as well as toughness of the tools have to be improved. For machining of low carbon steels, stainless steels and cast irons, coated cemented carbide indexable inserts are frequently used beside cermets and ceramic materials. For applications, were high thermal resistivity and wear resistance have to be covered with coatings up to 30 µm total thickness, chemical vapour deposition (CVD) is still state of the art. The single layer TiC, TiN and TiCN coatings developed in the last century have been extended to multilayer coatings, where the different benefits of the materials like hot hardness and oxidation resistance are combined. During the last two decades, the main efforts were to control and optimize the structure of the components, especially the Al2O3 phase and orientation. The adjustment of material properties, starting with the outermost zone of the substrate material, the applied coating layers and their interfaces in combination with the deposition parameters are necessary to obtain an optimized tool. This has also to be adjusted to the associated post treatment process, where the final properties of the coated indexable insert are achieved. The aims of recent investigations are to improve the understanding of the tribological system, in particular the generation of heat due to friction and plastic deformation of the chip in combination with the tool. In this complex system, the macroscopic scale of the coating system, i.e. layer thickness and layer architecture, have to be combined with the adjusted structures and material properties. Finally, the design of interfaces has to be conducted on an atomistic level, to achieve the desired adherence of the individual layers within the coating architecture and to the substrate. The residual stresses caused by the thermal mismatch of layer and substrate materials have to be taken into account in combination with the modification of stress level due to the post treatment. For a coating architecture with optimized performance, all of the above mentioned considerations have to be considered. Within this thesis and the enclosed publications, examples are shown how the cutting performance can be optimized by adjusted coating architecture and microstructure. A review is given about the development of CVD coatings for cutting tools, in parallel to the improvement of deposition technology as well as enhanced analytical methods. Furthermore, an outlook on new approaches for advanced coating systems and architectures is included, which can, in combination with sophisticated analytical methods, further enhance the performance of coated carbide cutting tools to fulfill the demands of future cutting applications.
Translated title of the contributionDesign von CVD Beschichtungen für Schneidwerkzeuge
Original languageEnglish
QualificationDr.mont.
Supervisors/Advisors
  • Mitterer, Christian, Assessor A (internal)
  • Kathrein, Martin, Co-Supervisor (external), External person
  • Antrekowitsch, Helmut, Assessor B (internal)
Publication statusPublished - 2013

Bibliographical note

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Keywords

  • CVD
  • cutting tool

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