Multi-layered Ruthenium-modified Bond Coats for Thermal Barrier Coatings

Diffusional approaches for fabrication of multi-layered Ru-modified bond coats for thermal barrier coatings have been developed via low activity chemical vapor deposition and high activity pack aluminization. Both processes yield bond coats comprising two distinct B2 layers, based on NiAl and RuAl, however, the position of these layers relative to the bond coat surface is reversed when switching processes. The structural evolution of each coating at various stages of the fabrication process has been and subsequent cyclic oxidation is presented, and the relevant interdiffusion and phase equilibria issues in are discussed. Evaluation of the oxidation behavior of these Ru-modified bond coat structures reveals that each B2 interlayer arrangement leads to the formation of α-Al 2 O 3 TGO at 1100°C, but the durability of the TGO is somewhat different and in need of further improvement in both cases

Prediction of delamination in multilayer artist paints under low amplitude fatigue loading

The objective of this study is to model the effect of low amplitude cyclic stresses on multilayer paint systems found in works of art. Acrylic gesso grounds with superimposed alkyd paint layers on canvas were investigated. Data from uniaxial testing of free-standing paint films was used to determine the constitutive properties of the paint. Peel tests were performed to determine the cohesive zone properties of the paint interface. A finite element model of a coating on a primed canvas substrate was subjected to combined cyclic and static mechanical loadings typically experienced by fine art paintings. Interface separation was controlled by an irreversible cohesive zone model that includes damage accumulation due to cyclic loading. Fatigue crack initiation times in years were predicted for various conditions including ordinary and extreme histories that paintings may experience in museum and conservation settings

Failure of Thin Films Under Low-Cycle Fatigue

Thin films or coatings applied on a substrate are utilised in a variety of applications such as microelectronics, optical coatings and protective coverings. As a consequence of changing environment (thermal and/or hygroscopic mismatch) or mechanical loadings these coatings are exposed to low-cycle fatigue, which can result in surface cracking, channelling, damage of the substrate, delamination along the film-substrate interface, etc. The performance of the application is heavily dependent on the mechanical integrity of the film and how it responds to a given loading. It is therefore vitally important that the failure mechanisms of the films/coatings are investigated. A numerical study is presented in which the finite element method has been used to consider the initiation and propagation of cracks in thin films applied to a substrate under low-cycle fatigue loading. A cohesive zone model incorporating a fatigue damage parameter in the traction-separation law to account for cyclic loading has been developed to consider two failure mechanisms. These are (i) a through-thickness crack in the film, arresting on the film-substrate interface and (ii) delamination along the film-substrate interface. Exposing both models to the same load cycles enables the calculation of time to first crack and which type of crack is more readily grown in the film-substrate system. Examples of where the current work is being used includes cracking in: (i) 16–18th century panel paintings on wood exposed to cyclic changes in temperature and/or relative humidity and (ii) oil tanker water ballast tank coatings under thermal stress cycles

Failure of Thin Films Under Low-Cycle Fatigue

Thin films or coatings applied on a substrate are utilised in a variety of applications such as microelectronics, optical coatings and protective coverings. As a consequence of changing environment (thermal and/or hygroscopic mismatch) or mechanical loadings these coatings are exposed to low-cycle fatigue, which can result in surface cracking, channelling, damage of the substrate, delamination along the film-substrate interface, etc. The performance of the application is heavily dependent on the mechanical integrity of the film and how it responds to a given loading. It is therefore vitally important that the failure mechanisms of the films/coatings are investigated. A numerical study is presented in which the finite element method has been used to consider the initiation and propagation of cracks in thin films applied to a substrate under low-cycle fatigue loading. A cohesive zone model incorporating a fatigue damage parameter in the traction-separation law to account for cyclic loading has been developed to consider two failure mechanisms. These are (i) a through-thickness crack in the film, arresting on the film-substrate interface and (ii) delamination along the film-substrate interface. Exposing both models to the same load cycles enables the calculation of time to first crack and which type of crack is more readily grown in the film-substrate system. Examples of where the current work is being used includes cracking in: (i) 16–18th century panel paintings on wood exposed to cyclic changes in temperature and/or relative humidity and (ii) oil tanker water ballast tank coatings under thermal stress cycles