Modelling of Metal-Coating Delamination Incorporating Variable Environmental Parameters

A mathematical model for metal-coat delamination of degrading metal was developed incorporating multiple variable environmental parameters. Metal-coat delamination not only depends on the electrochemical reactions at metal-coat interface but also on the factors like the type of propagating metal ions and their varying concentration with annual weather changes, time of exposure of the coated objects, type of coated objects are stationary or mobile vehicles, frequency with which certain vehicles are operating in various environments e.g. controlled or uncontrolled in terms of environmental conditions. A cutting edge model has been developed to calculate the varying environmental conditions using iteration algorithm, time dependent uncertain position of objects like vehicle in various environments using stochastic approach, effect of seasonal changes on ionic compound's concentration using algebraic method and instantaneous failure probability due to varying conditions. Based on the developed model a detailed simulation study was conducted to investigate the metal-coat delamination process and the ways to regress the under coat metal corrosion

A Review of Theoretical Analysis Techniques for Cracking and Corrosive Degradation of Film-Substrate Systems

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 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

A Novel Non-Destructive Sensing Technology for On-Site Corrosion Failure Evaluation of Coatings

The quality of coating and the resulting rate of corrosion of the underlying metal substrate can be measured by a variety of corrosion measurements (Tafel, Electrochemical Impedance Spectroscopy) by using standard laboratory electrochemical cells. However there is always a need of low cost, portable and non-destructive electrochemical cells which can be used on-site field for condition monitoring of large structures for example bridges and large infrastructures, complex operating systems as aircrafts, precision machines, petrochemical processes, automotive and locomotives. This research has developed state of the art cells and has commissioned for deploying this novel sensing technology for micro-defects detection, corrosion rate measurement and condition assessment of the defected coatings. Tafel measurement facilitated by these non-destructive cells is used to detect micro-defects and corrosion rate measurement while Electrochemical Impedance Spectroscopy measurement is facilitated to measure the coating condition. This technology has been successfully tested and commissioned on automotive, hazardous compartments with polymeric coatings and bridges to assess their coating condition in terms of their structural integrity. Post design testing involved the installation of these cells, running diagnostics, data acquisition and macrographs to predict structural defects and the resulting corrosion rate. This technology enables the design process to incorporate operational conditions and fully realize more durable and reliable solutions to be applied to high value large structures and complex interacting systems. Current developments in corrosion condition monitoring especially cost effective, non-destructive techniques to assess structural integrity beneath nonconductive and polymeric coating were long awaited. This reported development will revolutionise durability and reliability assessment techniques to enhance safety and mitigate catastrophic failures for cost savings and avoiding fatal accidents

A holistic mathematical modelling and simulation for cathodic delamination mechanism – a novel and an efficient approach

This paper addresses a holistic mathematical design using a novel approach for understanding the mechanism of cathodic delamination. The approach employed a set of interdependent parallel processes with each process representing: cation formation, oxygen reduction and cation transport mechanism, respectively. Novel mathematical equations have been developed for each of the processes based on the observations recorded from experimentation. These equations are then solved using efficient time-iterated algorithms. Each process consists of distinct algorithms which communicate with each other using duplex channels carrying signals. Each signal represents a distinct delamination parameter. As a result of interdependency of various processes and their parallel behaviour, it is much easier to analyse the quantitative agreement between various delamination parameters. The developed modelling approach provides an efficient and reliable prediction method for the delamination failure. The results obtained are in good agreement with the previously reported experimental interpretations and numerical results. This model provides a foundation for the future research within the area of coating failure analysis and prediction

Templating Nanostructured Aromatic Based Materials as Possible Anode Electrodes for Na-ion Batteries: A Computational DFT Approach

Due to their widespread availability and lower costs Na-ion batteries have grabbed attention as a promising substitute for lithium-ion batteries. In this paper, we delve into a computational investigation of the potential use of 2,4-Chloronitrotoluene and pyrazine as electrode materials for SIBs. We utilized Density Functional Theory (DFT) calculations to examine their properties and suitability for energy storage applications. Adsorption energies, highest occupied molecular orbital, lowest unoccupied molecular orbital, HLG energies, total energies, and bond lengths were computed using computational theories for aromatic compounds. This computation is based here on the DFT and computational engineering modelling approach. The results indicate that both 2,4-chloronitrotoluene and pyrazine exhibit favorable adsorption energies for Na-ion adsorption, indicating their potential as electrode materials. Furthermore, the investigation delved into the electronic properties of the materials. Notably, the analysis showed that the EHOMO, ELUMO, and EHLG are facilitative to the efficient transfer of electrons during the operation of the battery. Moreover, the computed bond lengths indicate that stable Na-ion adsorption can appear on both materials, further solidifying their potential for integration into the framework of Na-ion batteries. In essence, this study yields valuable insights into the electrochemical aspects of 2,4- chloronitrotoluene and pyrazine, highlighting their promising candidacy as electrode materials for SIBs

Fabrication and characterisation of electrodeposited and magnetron sputtered thin films

The MnO-Zn thin films were fabricated by radio frequency (RF) magnetron sputtering and compared with pulse electrodeposition (PED) Zn thin films, doped with MnO and ZrO nanoparticles. Surface morphology, structural properties, chemical composition and corrosion resistance of these coatings were investigated by using Scanning Electron Microscopic (SEM), X-ray Diffraction (XRD), Energy-dispersive X-ray Spectroscopy (EDS), 3-D Scanning Interferometry and environmental chamber. Surface morphology and degree of crystallinity have different behaviour for differen t deposi tion method. Pulse coated films have polycrystalline structure with high surface roughness (Ra) whereas sputtered films are mono-crystalline with reduced roughness (Ra). Corrosion tests of both RF sputter and PED films revealed that the distribution of corrosion products formed on the surface of sputter films were not severe in extent as in case of electrodeposited coatings. Results showed that the doping of ZrO nano-sized particles in Zn matrix and Mn-Zn composite films significantly improved the corrosion resistance of PED thin films

Sensor based corrosion condition monitoring of coating substrate system informed by fracture mechanics, electrochemistry and heat transfer concepts

This research investigates delamination and blistering as coating failure mechanisms due to corrosive diffusing species, residual and thermal stresses. Several mathematical models to include environmental variables as temperature, humidity ratio and atmospheric constituents have been developed and reported. During this study various coating failures have been analysed through a combination of electrochemistry, fracture mechanics and heat transfer concepts. This approach enabled the development of comprehensive mathematical models for the prediction and prognoses of coating failures applied to high value assets. The formation of blister and its propagation due to diffusion of corrosive species was investigated. Fracture mechanics concepts were utilised to study the initiation and propagation of a circular blister as an interfacial crack under the coupling affects of compressive and diffusion induced stresses along with heat transfer due to pressure gradient at the interface of coating substrate system. The direction of blister propagation was defined through a mathematical model with blister radius r and radial angle θ as initial defining parameters. Experimental work was conducted to assess the influence of varying temperatures, humidity ratios and environmental pollutants as SO2 and salt particles to investigate corrosion failures. Live condition monitoring techniques were developed to assess corrosion rate with respect to large vehicles operation frequencies to study the effects of changing environments. Three years of real time data consisted of 150K data points was acquired for investigating corrosion failures with or without coatings. Both experimental and simulation data was compared to predictive and prognostics models. There is excellent agreement between experimental and simulation results to be applied for live corrosion condition monitoring of large high value assets. A sensor based corrosion condition monitoring methodology, informed by experimental and simulation results has been developed and is presented

A Unified Mathematical Modelling and Simulation for Cathodic Blistering Mechanism incorporating diffusion and fracture mechanics concepts

A novel mathematical model has been developed to understand the mechanism of blister initiation and propagation. The model employs a two-part theoretical approach encompassing the debondment of a coating film from the substrate, coupled with the design components incorporating diffusion and fracture mechanics, where the latter is derived from equi-biaxial tensile loading. Integrating the two components, a comprehensive mathematical design for the propagation of blister boundaries based on specific toughness functions and mode adjustment parameters has been developed. This approach provided a reliable and efficient prediction method for blister growth rate and mechanisms. The model provided a foundation for holistic design based on diffusion and mechanic components to enable better understanding of the debondment of thin elastic films bonded to a metallic substrate

Electrochemical Corrosion Failure Analysis of Large Complex Engineering Structures by using LPR Sensors

This paper presents the effects of three major parameters; temperature, relative humidity and hygroscopic salts contaminants on the atmospheric corrosion of large steel structures. The effects of these three parameters have been analysed by using micro-sized LPR sensors to continuously monitor the corrosion rate of a degrading large structure under varying parameters. A long term, three years study was performed by deploying LPRs on strategically selected large military vehicles (main battlefield tanks), which are stationed in the Tank Museum at Bovington, UK. These vehicles are operational and are of historic significance with cultural biography, however structural deterioration through corrosion, corrosion fatigue, stress corrosion cracking and mechanical failures are a threat to these vehicles in terms of their conservation. A set of vehicles operational (uncontrolled environment) and non-operational (controlled environment) was selected for comparative analysis in context of corrosion rate. This research is founded on a novel real-time corrosion monitoring technique that enables to better understand the relationship between varying environmental parameters and corrosion rate of large steel-based mobile structures during operation. This research provides a synthesis of real time corrosion data, which has been accumulated over a period of three years. An overview of structural deterioration is presented and derived from a significantly large data, therefore it provides a more reliable and highly accurate assessment of failures due to corrosion

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

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