TY - BOOK

T1 - Cross-sectional Characterisation of Thin Films for the Knowledge-based Design of Hard Coatings

AU - Gruber, David

N1 - embargoed until null

PY - 2021

Y1 - 2021

N2 - Thin films are used in a wide range of applications due to their unique functional properties. One particular role is the protections of cutting and milling tools by hard thin coatings. This results in significantly improved tool lifetime and performance. Most thin films exhibit cross-sectional (i.e. depth) gradients of microstructure, mechanical and functional properties. These gradients can be connected to specific conditions during film growth from the vapour phase, or be the consequence of exposure to post-deposition external factors, e.g. mechanical or thermal loads or oxidation. The gradients are decisively linked to functional performance in a large number of thin film applications, including hard coatings on cutting tools. Their characterisation is of critical importance in establishing structure-property relationships and the knowledge-based improvement and design of thin films. Measuring nano-scale thin film structure and property gradients requires dedicated high-resolution experimental techniques. In order to resolve sub-micrometre thin film features and their physical properties, synchrotron X-ray nano-diffraction, nano-indentation, electron microscopy as well as micro-cantilever bending experiments were applied within the framework of this thesis. In addition to the critical role of structure and property gradients within thin protective coatings on cutting tools, also the behaviour of the coating-near substrate region is of great interest for the understanding and modelling of cutting and milling processes. Part of this thesis is concerned with investigating the behaviour of substrate-near WC-Co regions when subjected to cyclic thermal shocks by laser irradiation. This thesis presents two model cases of cross-sectional nano-analytics based characterisation of thin films, while a third study presented examines plastification phenomena in coating-near WC-Co substrate regions. In particular, the presented case studies are: A study of the surface-oxidation behaviour of a CVD TiN/TiB2 protective coating, applying synchrotron X-ray nano-diffraction, transmission electron microscopy and in-situ micro-cantilever experiments. This allowed to examine the effect of surface oxidation on gradients of microstructure, residual stress and mechanical properties in detail, proving the favourable oxidation resistance of the TiB2 sublayer. A cross-sectional study of a CVD diamond coating, consisting of a nanocrystalline bottom layer and a coarse-grained polycrystalline top layer. Complex cross-sectional correlations between thin film microstructure, residual stress, mechanical properties and deposition conditions could be revealed by synchrotron X-ray nano-diffraction, transmission electron microscopy and in-situ micro-cantilever experiments. A study involving a complex synchrotron X-ray diffraction set-up with in-situ laser pulsing to characterise the time-dependent evolution of stresses and microstructure in locally irradiated WC-Co inserts coated with cvd with TiCN and alpha-Al2O3 films. With this set-up, the temperature and time dependent development of stress levels within the coating-near WC-Co substrate region could be recorded at millisecond time resolution. The acquired data provided detailed insight into the WC-Co composite plastification mechanism which governed the stress build-up and relaxation in the substrate material.

AB - Thin films are used in a wide range of applications due to their unique functional properties. One particular role is the protections of cutting and milling tools by hard thin coatings. This results in significantly improved tool lifetime and performance. Most thin films exhibit cross-sectional (i.e. depth) gradients of microstructure, mechanical and functional properties. These gradients can be connected to specific conditions during film growth from the vapour phase, or be the consequence of exposure to post-deposition external factors, e.g. mechanical or thermal loads or oxidation. The gradients are decisively linked to functional performance in a large number of thin film applications, including hard coatings on cutting tools. Their characterisation is of critical importance in establishing structure-property relationships and the knowledge-based improvement and design of thin films. Measuring nano-scale thin film structure and property gradients requires dedicated high-resolution experimental techniques. In order to resolve sub-micrometre thin film features and their physical properties, synchrotron X-ray nano-diffraction, nano-indentation, electron microscopy as well as micro-cantilever bending experiments were applied within the framework of this thesis. In addition to the critical role of structure and property gradients within thin protective coatings on cutting tools, also the behaviour of the coating-near substrate region is of great interest for the understanding and modelling of cutting and milling processes. Part of this thesis is concerned with investigating the behaviour of substrate-near WC-Co regions when subjected to cyclic thermal shocks by laser irradiation. This thesis presents two model cases of cross-sectional nano-analytics based characterisation of thin films, while a third study presented examines plastification phenomena in coating-near WC-Co substrate regions. In particular, the presented case studies are: A study of the surface-oxidation behaviour of a CVD TiN/TiB2 protective coating, applying synchrotron X-ray nano-diffraction, transmission electron microscopy and in-situ micro-cantilever experiments. This allowed to examine the effect of surface oxidation on gradients of microstructure, residual stress and mechanical properties in detail, proving the favourable oxidation resistance of the TiB2 sublayer. A cross-sectional study of a CVD diamond coating, consisting of a nanocrystalline bottom layer and a coarse-grained polycrystalline top layer. Complex cross-sectional correlations between thin film microstructure, residual stress, mechanical properties and deposition conditions could be revealed by synchrotron X-ray nano-diffraction, transmission electron microscopy and in-situ micro-cantilever experiments. A study involving a complex synchrotron X-ray diffraction set-up with in-situ laser pulsing to characterise the time-dependent evolution of stresses and microstructure in locally irradiated WC-Co inserts coated with cvd with TiCN and alpha-Al2O3 films. With this set-up, the temperature and time dependent development of stress levels within the coating-near WC-Co substrate region could be recorded at millisecond time resolution. The acquired data provided detailed insight into the WC-Co composite plastification mechanism which governed the stress build-up and relaxation in the substrate material.

KW - thin film

KW - XRD

KW - hard coatings

KW - thin film characterization

KW - synchrotron XRD

KW - synchrotron X-ray nano-diffraction

KW - cross-sectional thin film characterisation

KW - micromechanical testing

KW - micro-cantilever

KW - nanoindentation

KW - plastification

KW - laser pulsing

KW - TiB2

KW - CVD diamond

KW - oxidation

KW - cutting tools

KW - Dünnschicht

KW - Hartstoffschichten

KW - Schichtcharakterisierung

KW - Tiefencharakterisierung

KW - XRD

KW - Röntgenbeugung

KW - Synchrotron-Röntgenbeugung

KW - TiB2

KW - CVD-Diamant

KW - Mikromechanik

KW - Nanoindentation

KW - Nanostrahl-Röntgenbeugung

KW - wissensbasierte Schichtentwicklung

KW - Plastifizierung

KW - Oxidation

M3 - Doctoral Thesis

ER -