ZrN-based hard coatings deposited by chemical and physical vapor deposition
Research output: Thesis › Doctoral Thesis
Hard coatings have been widely used for several decades to enhance the performance and efficiency of cemented carbide cutting tools in machining applications. The requirements for these coatings are a high hardness and wear resistance, as well as a good thermal stability and oxidation resistance. Chemical and physical vapor deposition (CVD and PVD) are common methods to deposit these coatings. The goal of this work is the development of ZrN-based hard coatings and the in-depth characterization of their microstructure, mechanical properties and thermal properties. In order to enhance the coating properties different approaches were applied. In the first approach, the influence of the addition of C to CVD ZrN on the mentioned properties was investigated. It was found that the hardness increases for coatings containing C, which can be attributed to grain refinement and stronger covalent bonding. A detailed investigation of the oxidation behavior with in-situ high-temperature synchrotron X-ray diffraction showed that the presence of C increases the oxidation stability, where the ZrC0.4N0.6 coating showed the highest oxidation onset temperature of ~570 °C. The higher oxidation resistance in ZrC0.4N0.6 and ZrC compared to ZrN can be attributed to the stabilization of the cubic and/or tetragonal ZrO2 phase by residual amorphous C and a smaller grain size. In the second approach, ZrN/Ti(Al)N multilayer coatings were deposited with PVD and the influence of the bilayer thickness on the microstructure and mechanical properties was investigated. Firstly, ZrN/TiN multilayer coatings with different bilayer thickness, as well as ZrN and TiN single-layer coatings were studied. It was found that the multilayer architecture increases the hardness, as well as the fracture stress compared to the single-layer coatings. Secondly, the microstructure and residual stress of a graded ZrN/Ti0.33Al0.67N coating with constant Ti0.33Al0.67N and stepwise increasing ZrN individual layer thickness was investigated in detail using position resolved cross-sectional X-ray nanodiffraction. A (semi-)coherent layer growth and an increasing grain size, as well as a decreasing compressive residual stress state with increasing ZrN layer thickness was observed. To summarize, this thesis highlights several approaches to enhance the properties of CVD and PVD ZrN-based coatings. Furthermore, the importance of advanced high-resolution in-situ and position resolved investigation methods for the characterization of hard coatings is emphasized, which contribute to a deeper understanding of the deposition-structure-property relation of ZrN-based hard coatings.
|Translated title of the contribution||ZrN basierte Hartstoffschichten abgeschieden mittels chemischer und physikalischer Gasphasenabscheidung|
|Publication status||Published - 2022|