TY - BOOK

T1 - Modelling of the post-treatment of coating/substrate architectures

AU - Faksa, Lukas

N1 - embargoed until 20-05-2024

PY - 2019

Y1 - 2019

N2 - The thesis focuses on the simulation of a part of a production chain process, namely the post-production treatment of chemical vapour deposited (CVD) WC-Co hard metal cutting tool inserts. The commonly used CVD coatings of WC-Co such as TiN, TiCN or Al2O3 often exhibit a crack network and tensile stresses in their structures. These cracks are disadvantageous for the performance and durability of cutting tool inserts. The work examines the reasons for these detrimental phenomena and investigates possibilities how to prevent them in three main topics - “Crack growth assessment during cooling from deposition temperature”, “Shot peening and its influence on residual stresses and cracks” and “Investigation of the influence of cooling/heating and shot peening treatment on hard metal microstructures”. The first topic deals with a finite element (FE) investigation of crack growth in the cutting tool inserts during cooling from deposition temperature to room temperature. The stresses during and after cooling are calculated in Al2O3/TiCN coatings and WC-Co substrate. A minimal initial crack is assumed to be present at the beginning of the cooling process to trigger further crack propagation. The final crack length at the end of the cooling process is calculated. The validity of the calculations is confirmed with measurements and the metallographic evidence. The second topic deals with FE simulation of conventional dry shot peening of CVD Al2O3/TiCN coated WC-Co hard metal - a post treatment process that is supposed to introduce compressive stresses into the cutting tool insert layers and close the initially opened cracks arisen due to cooling of the CVD coatings from deposition temperature. The influence of several shot peening parameters on the residual stress development is investigated and the stresses are compared with literature values. Recommendations and shot peening parameters that help to introduce compressive stresses and close the cracks in the cutting tool structures are presented. Additionally, the effectiveness of the crack closure is evaluated in terms of shot peening parameters. The model is validated with literature measurements. The third topic investigates the influence of the deposition and the shot peening process on the stress-strain state of the Al2O3 and TiCN coated inserts. Using the FE method, the microstructure of the WC-Co hard metal is modelled and the stresses in the single phases are calculated. All necessary material data are taken either from literature or are obtained from measurements. A special focus is put on the plastification of WC, as an EBSD analysis of compressively loaded hard metals shows some plastification in the WC grains already at room temperature. The plastic behaviour of WC is inversely reconstructed and used in the simulations.

AB - The thesis focuses on the simulation of a part of a production chain process, namely the post-production treatment of chemical vapour deposited (CVD) WC-Co hard metal cutting tool inserts. The commonly used CVD coatings of WC-Co such as TiN, TiCN or Al2O3 often exhibit a crack network and tensile stresses in their structures. These cracks are disadvantageous for the performance and durability of cutting tool inserts. The work examines the reasons for these detrimental phenomena and investigates possibilities how to prevent them in three main topics - “Crack growth assessment during cooling from deposition temperature”, “Shot peening and its influence on residual stresses and cracks” and “Investigation of the influence of cooling/heating and shot peening treatment on hard metal microstructures”. The first topic deals with a finite element (FE) investigation of crack growth in the cutting tool inserts during cooling from deposition temperature to room temperature. The stresses during and after cooling are calculated in Al2O3/TiCN coatings and WC-Co substrate. A minimal initial crack is assumed to be present at the beginning of the cooling process to trigger further crack propagation. The final crack length at the end of the cooling process is calculated. The validity of the calculations is confirmed with measurements and the metallographic evidence. The second topic deals with FE simulation of conventional dry shot peening of CVD Al2O3/TiCN coated WC-Co hard metal - a post treatment process that is supposed to introduce compressive stresses into the cutting tool insert layers and close the initially opened cracks arisen due to cooling of the CVD coatings from deposition temperature. The influence of several shot peening parameters on the residual stress development is investigated and the stresses are compared with literature values. Recommendations and shot peening parameters that help to introduce compressive stresses and close the cracks in the cutting tool structures are presented. Additionally, the effectiveness of the crack closure is evaluated in terms of shot peening parameters. The model is validated with literature measurements. The third topic investigates the influence of the deposition and the shot peening process on the stress-strain state of the Al2O3 and TiCN coated inserts. Using the FE method, the microstructure of the WC-Co hard metal is modelled and the stresses in the single phases are calculated. All necessary material data are taken either from literature or are obtained from measurements. A special focus is put on the plastification of WC, as an EBSD analysis of compressively loaded hard metals shows some plastification in the WC grains already at room temperature. The plastic behaviour of WC is inversely reconstructed and used in the simulations.

KW - WC-Co Hartmetall

KW - Beschichtungen

KW - Kugelstrahlen

KW - Wendeschneidplatte

KW - Eigenspannungen

KW - Risse

KW - WC-Co hard metal

KW - Hard coatings

KW - Shot peening

KW - Cutting tool insert

KW - Residual stresses

KW - Cracks

M3 - Doctoral Thesis

ER -