TY - THES

T1 - Contact modeling of CVD coatings for cutting tools

AU - Brettner, Elisabeth

N1 - embargoed until 09-03-2016

PY - 2011

Y1 - 2011

N2 - The purpose of this work was to find a strategy for optimizing CVD layered thin film coatings for cutting applications. The approach used is based on a combination of indentation experiments, to determine the mechanical properties, i.e. elastic modulus and hardness of the coatings, and the commercial analytical simulation package ELASTICA, to calculate the stress imposed by external mechanical loads within the individual layers. The system of interest comprises of the WC-Co substrate, a TiCN base layer, a TiCO bonding layer and α- or κ-Al2O3 as top layer. The simulations were first done on one-layer systems and afterwards on the three-layer system under particular load and indenter radius situations and with internal compressive stress. In all investigations, similar results regarding to the influence of the force, indenter radius, layer thickness, elastic modulus and internal compressive stress can be obtained. The higher the force and indenter radius is, the smaller is the von Mises stress because of the smaller contact pressure per unit area; but due to the higher force, the maximum is located deeper in the system. The influence of the layer thickness depends on the difference of the elastic modulus between the substrate and the coating. If the elastic modulus of the substrate is much higher, which means the material is stiffer, its influence is more pronounced for a thinner layer, and thus a thinner layer could seem to be stiffer resulting in a higher von Mises stress. Generally, a higher elastic modulus leads to a higher von Mises stress because of the higher stiffness of the material. Because of the different elastic moduli of the substrate and the different layers, steps at the interfaces can be observed. Introducing internal compressive stress in the Al2O3 top layer leads to an increase of the von Mises stress and the step at the interface between Al2O3 and TiCO. In conclusion, by modeling it is possible to illustrate how the stress is distributed within the coating system and where the maximum is located. Thus, critical areas of the layer system can be determined and by varying the different parameters, i.e. layer thickness, elastic modulus or compressive stress, it is possible to affect the position of the maximum von Mises stress.

AB - The purpose of this work was to find a strategy for optimizing CVD layered thin film coatings for cutting applications. The approach used is based on a combination of indentation experiments, to determine the mechanical properties, i.e. elastic modulus and hardness of the coatings, and the commercial analytical simulation package ELASTICA, to calculate the stress imposed by external mechanical loads within the individual layers. The system of interest comprises of the WC-Co substrate, a TiCN base layer, a TiCO bonding layer and α- or κ-Al2O3 as top layer. The simulations were first done on one-layer systems and afterwards on the three-layer system under particular load and indenter radius situations and with internal compressive stress. In all investigations, similar results regarding to the influence of the force, indenter radius, layer thickness, elastic modulus and internal compressive stress can be obtained. The higher the force and indenter radius is, the smaller is the von Mises stress because of the smaller contact pressure per unit area; but due to the higher force, the maximum is located deeper in the system. The influence of the layer thickness depends on the difference of the elastic modulus between the substrate and the coating. If the elastic modulus of the substrate is much higher, which means the material is stiffer, its influence is more pronounced for a thinner layer, and thus a thinner layer could seem to be stiffer resulting in a higher von Mises stress. Generally, a higher elastic modulus leads to a higher von Mises stress because of the higher stiffness of the material. Because of the different elastic moduli of the substrate and the different layers, steps at the interfaces can be observed. Introducing internal compressive stress in the Al2O3 top layer leads to an increase of the von Mises stress and the step at the interface between Al2O3 and TiCO. In conclusion, by modeling it is possible to illustrate how the stress is distributed within the coating system and where the maximum is located. Thus, critical areas of the layer system can be determined and by varying the different parameters, i.e. layer thickness, elastic modulus or compressive stress, it is possible to affect the position of the maximum von Mises stress.

KW - CVD Beschichtungen

KW - Zerspannungswerkzeug

KW - Indentation Experimente

KW - Simulation

KW - äussere mechanische Belastung

KW - Eigenspannung

KW - CVD coatings

KW - cutting tools

KW - indentation experiment

KW - simulation

KW - external mechanical stress

KW - internal stress

M3 - Diploma Thesis

ER -