Advanced characterization techniques for the knowledge-based design of hard coatings

Research output: ThesisDoctoral Thesis

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Abstract

In the recent years, the interest in cross-sectional and high temperature characterization techniques as well as in the determination of the thermo-physical properties of hard and wear resistant coatings has gradually increased. Thus, the aim of the present thesis is the evaluation and further enhancement as well as the establishment of novel advanced characterization techniques for hard coatings used for wear protection of tools. To elaborate the influence of deposition process inherent growth defects, i.e. droplets, on the wear behavior of arc evaporated TiAlTaN coatings, a combination of focused ion beam cut and slice techniques, energy dispersive X-ray spectroscopy and grayscale image correlation was applied to wear tracks of samples after ball-on-disk testing at room temperature and 700 °C. Employing this combinatorial approach provided the possibility to perform surface and cross-sectional analysis as well as tomographical investigations of selected droplets, which enabled the investigation of their contribution to the tribological response of the coating. For the investigation of stress-depth gradients of chemical vapor deposited alpha-Al2O3 coatings, exhibiting a grain size in the micrometer range, with high vertical resolution, the recently introduced synchrotron X-ray nanodiffraction approach was modified. An X-ray beam with dimensions of 100 nm in height and 10 µm width was implemented at the beamline ID 13 at the European Synchrotron Radiation facility. The measurements revealed different stress gradients, introduced by blasting treatments with different blasting media, with outstanding accuracy and resolution. As instruments for the assessment of the thermo-physical properties, i.e. thermal conductivity, heat capacity and thermal expansion of wear resistant coatings, a portfolio of techniques was evaluated. Biaxial stress temperature measurements and high temperature X-ray diffraction were both successfully applied to reveal the coefficient of thermal expansion of TiN, AlN and TiAlN coatings with reasonable agreement. The thermal conductivity of TiAlN coatings with different microstructures before and after annealing was compared using time-domain thermoreflectance in order to investigate the effect of microstructural changes on the thermal conductivity. Differential scanning calorimetry yielded specific heat capacities for TiN, AlN and TiAlN coatings, which were in excellent agreement with values provided by the National Institute of Standards and Technology.
Translated title of the contributionModerne Charakterisierungsmethoden für das wissensbasierte Design von Hartstoffschichten
Original languageEnglish
QualificationDr.mont.
Awarding Institution
  • Montanuniversität
Supervisors/Advisors
  • Keckes, Jozef, Assessor B (internal)
  • Mitterer, Christian, Assessor A (internal)
Publication statusPublished - 2015

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