TY - THES

T1 - Numerical Analysis of Residual Stress and Crack Networks in CVD Multilayer Coated Cutting Tools

AU - Velic, Dino

N1 - embargoed until 18-10-2023

PY - 2018

Y1 - 2018

N2 - The aim of this study is to investigate residual stresses and crack systems in multilayer coated cutting tools. The cutting tool insert is a hard metal tungsten carbide substrate with cobalt binder phase produced in a powder metallurgic sintering process. The coatings either consist of a single TiCN layer or a TiCN base-layer and an Al2O3 top-layer, both produced with chemical vapor deposition (CVD). During the cooling process after deposition, residual stresses and crack systems evolve, due to the various coefficients of thermal expansion of coatings and substrate. A 2D Abaqus standard Finite Element model is used to emulate the process and clarify how cracks could be avoided or their number and size minimized. The surface roughness of the layers and the substrate, which is an essential parameter, is extracted from SEM cross section images, digitalized and included in the simulation. A parametric study reveals the impact of coating thickness of the layers on the obtained residual stresses. Furthermore, a correlation between crack distance, different cobalt content of the substrate material and residual stress is investigated. The residual stress development for the cooling process is analyzed and illustrated. Numerically calculated residual stress values are compared with experimental measurements to validate the simulations. In addition, a tri-layer coating system, consisting of a TiCN base-layer, an Al2O3 middle-layer and a TiN top-layer is introduced and analyzed.

AB - The aim of this study is to investigate residual stresses and crack systems in multilayer coated cutting tools. The cutting tool insert is a hard metal tungsten carbide substrate with cobalt binder phase produced in a powder metallurgic sintering process. The coatings either consist of a single TiCN layer or a TiCN base-layer and an Al2O3 top-layer, both produced with chemical vapor deposition (CVD). During the cooling process after deposition, residual stresses and crack systems evolve, due to the various coefficients of thermal expansion of coatings and substrate. A 2D Abaqus standard Finite Element model is used to emulate the process and clarify how cracks could be avoided or their number and size minimized. The surface roughness of the layers and the substrate, which is an essential parameter, is extracted from SEM cross section images, digitalized and included in the simulation. A parametric study reveals the impact of coating thickness of the layers on the obtained residual stresses. Furthermore, a correlation between crack distance, different cobalt content of the substrate material and residual stress is investigated. The residual stress development for the cooling process is analyzed and illustrated. Numerically calculated residual stress values are compared with experimental measurements to validate the simulations. In addition, a tri-layer coating system, consisting of a TiCN base-layer, an Al2O3 middle-layer and a TiN top-layer is introduced and analyzed.

KW - CVD

KW - Beschichtungen

KW - Hartmetall Werkzeuge

KW - Schneidprozess

KW - Finite Elemente

KW - CVD

KW - cutting

KW - hardmetal tools

KW - finite element method

KW - coating

M3 - Master's Thesis

ER -