Microstructural and Mechanical Properties of Si-alloyed AlCrN Hard Coatings: Grain Boundary Segregation Engineering by CrN Precipitation

Research output: ThesisMaster's Thesis

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Abstract

In the race for hard and simultaneously tough hard coatings, for applications in the metal cutting industry, this thesis takes aim to propose grain boundary segregation engineering as a viable tool to improve mechanical properties of well-established Transition Metal Nitrides, such as AlCrN. Therefore, in a first step a gradient coating with increasing Si content was deposited by cathodic arc evaporation. This coating was annealed at different temperatures of up to 1100 °C and characterized by cross sectional X-ray nanodiffraction (CSnanoXRD) at the synchrotron source PETRA III at the German Synchrotron (DESY). Measured intensity plots of wide-angle X-ray scattering (WAXS) revealed the formation of a wurtzite (w-) AlN phase with cubic (c-) CrN precipitates and the formation of a nanocomposite structure after alloying with Si. Additionally, small-angle X-ray scattering (SAXS) data indicated the formation of 12 nm thick nanolayers in the Si-free zone of the coating, which abruptly changes to a periodicity of 25 nm after the introduction of Si. This data collected from the gradient coating was further used for the design of two reference coatings with a composition of Al0,8Cr0,2N and (Al0,7Cr0,3)0,9Si0,1N and two additional multilayered coatings of alternating composition of the two reference ones. These four coatings were tested for their mechanical properties by in situ cantilever bending experiments and displayed fracture stresses of up to 4.8 GPa and fracture toughness values of up to 2.8 MPam1/2. Through this effort we provide information on the importance of precise annealing parameters when dealing with grain boundary segregation engineering as well as limits that are inherent to this method.
Translated title of the contributionMikrostrukturelle und Mechanische Eigenschaften von Si-legierten AlCrN Beschichtungen: Möglichkeiten zu Korngrenzendesign durch Segregation von CrN
Original languageEnglish
QualificationDipl.-Ing.
Awarding Institution
  • Montanuniversität
Supervisors/Advisors
  • Keckes, Jozef, Supervisor (internal)
Award date25 Jun 2021
Publication statusPublished - 2021

Bibliographical note

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Keywords

  • Hard Coating
  • AlCrN
  • Cathodic Arc Evaporation
  • Grain Boundary Segregation
  • Cross sectional X-ray nanodiffraction
  • in situ cantilever bending

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