Coatings for hot section gas turbine components

Engineering Failure Analysis

2017

This paper contains a review of the most vital concepts regarding the analysis and design of film systems. Various techniques have been presented to analyse and predict the failure of films for all common types of failure: fracture, delamination, general yield, cathodic blistering, erosive and corrosive wear in both organic and inorganic films. Interfacial fracture or delamination is the loss of bonding strength of film from substrate, and is normally analysed based on the fracture mechanics concepts of bi-material systems. Therefore, keeping the focus of this review on bonding strength, the emphasis will be on the interfacial cracking of films and the corresponding stresses responsible for driving the delamination process. The bi-material characteristics of film systems make the nature of interfacial cracks as mixed mode, with cracks exhibiting various complex patterns such as telephone cord blisters. Such interfacial fracture phenomenon has been widely studied by using fracture mechanics based applicable analysis to model and predict the fracture strength of interface in film systems. The incorporation of interfacial fracture mechanics concepts with the thermodynamics/diffusion concepts further leads to the development of corrosive degradation theories of film systems such as cathodic blistering. This review presents the suggestions for improvements in existing analysis techniques to overcome some of the limitations in film failure modelling. This comprehensive review will help researchers, scientists, and academics to understand, develop and improve the existing models and methods of film-substrate systems.

Section: Gmentioning

confidence: 99%

A review of theoretical analysis techniques for cracking and corrosive degradation of film-substrate systems

Engineering Failure Analysis

2017

“…Later on, the elastic energy release rate was formulated as a function of coating thickness and stiffness, blister height, and pressure (Bressers, Peteves, & Steen, 2000;Galindo, Van Veen, Evans, Schut, & de Hosson, 2005). The mathematical relation for energy release rate as a function of coating stiffness, pressure, height and radius of height was developed in (Kappes, Frankel, & Sridhar, 2010).…”

Section: Prognostic Modelling Of Corrosion and Coating Failurementioning

confidence: 99%

An optimal condition based maintenance scheduling for metal structures based on a multidisciplinary research approach

Latif

Structure and Infrastructure Engineering

et al. 2019

Latest research findings show that the deterioration of metal coatings results due to complex combination of material and meteorological parameters. The classical maintenance scheduling do not consider complex interface of materials and meteorological parameters to determine optimal maintenance framework. The cost of recoating can be optimised through appropriate selection of coating specifications and maintenance strategy. This research provides a multidisciplinary algorithmic approach to determine cost-effective solutions for recoating. The specifications of red oxide primer coating and structural steel substrate system are considered for simulation analysis. The results show that the appropriate selection of 10% increase in coating thickness based on coatingsubstrate system specifications resulted in 20-25% reduction in annual patch failures which reduces 5-6 % cost of recoating. Furthermore, the proposed model also simulated to compare Patch recoating and Part recoating strategy and algorithm show that the Part recoating is cost-effective as compared to Patch recoating if number of annual patch failure is greater than '2' and area of the part is '2x'times larger than the area of the patch. Contrary, the Patch recoating results in low cost if the part area is '10x' times larger than patch area and number of annual patch failures are less than '7'.

“…The analysis is performed within the framework of thermodynamics coupled with mechanics. The novelty within this research is the utilisation of two-part theoretical approach for circular blister nucleation and propagation incorporating the effects of coating microcracks, which has not been used in previous blistering models [46][47][48][49][50][51][52]. The combination of thermodynamics and mechanics approaches provides a novel technique to understand coating failures with micro-cracks.…”

Section: Introductionmentioning

confidence: 99%

Analysing the coupled effects of compressive and diffusion induced stresses on the nucleation and propagation of circular coating blisters in the presence of micro-cracks

Engineering Failure Analysis

Stokes

2016

This paper presents the delamination of coating with micro-cracks under compressive residual stress coupled with diffusion induced stress. Micro-cracks in coating provide a passage for corrosive species towards the coating-substrate interface which in turn produces diffusion induced stress in the coating. Micro-cracks contract gradually with increasing compressive residual stress in coating due to thermal expansion mismatch which blocks the species diffusion towards the interface. This behaviour reduces the diffusion induced stress in the coating while the compressive residual stress increases. With further increase in compressive residual stress, micro-cracks reach to the point, where they cannot be constricted any further and a high compressive residual stress causes the coating to buckle away from the substrate resulting in delamination and therefore initiating blistering. Blistering causes the contracted micro-cracks to wide open again which increases diffusion induced stress along with high compressive residual stress. The high resultant stress in coating causes the blister to propagate in an axis-symmetric circular pattern. A two-part theoretical approach has been utilised coupling the thermodynamic concepts with the mechanics concepts. The thermodynamic concepts involve the corrosive species transportation through micro-cracks under increasing compression, eventually causing blistering, while the fracture mechanics concepts are used to treat the blister growth as circular defect propagation. The influences of moduli ratio, thickness ratio, thermal mismatch ratio, poisson's ratio and interface roughness on blister growth are discussed. Experiment is reported for blistering to allow visualisation of interface and to permit coupled (diffusion and residual) stresses in the coating over a full range of interest. The predictions from model show excellent, quantitative agreement with the experimental results.