Zulfiqar Ahmad Khan

Optimisation of interface roughness and coating thickness to maximise coating–substrate adhesion – a failure prediction and reliability assessment modelling

A mathematical model for failure prediction and reliability assessment of coating–substrate system is developed based on a multidisciplinary approach. Two models for diffusion and bending of bi-layer cantilever beam have been designed separately based on the concepts of material science and solid mechanics respectively. Then, these two models are integrated to design an equation for debonding driving force under mesomechanics concepts. Mesomechanics seeks to apply the concepts of solid mechanics to microstructural constituent of materials such as coatings. This research takes the concepts of mesomechanics to the next level in order to predict the performance and assess the reliability of coatings based on the measure of debonding driving force. The effects of two parameters i.e. interface roughness and coating thickness on debonding driving force have been analysed using finite difference method. Critical/threshold value of debonding driving force is calculated which defines the point of failure of coating–substrate system and can be used for failure prediction and reliability assessment by defining three conditions of performance i.e. safe, critical and fail. Results reveal that debonding driving force decreases with an increase in interface roughness and coating thickness. However, this is subject to condition that the material properties of coating such as diffusivity should not increase and Young’s modulus should not decrease with an increase in the interface roughness and coating thickness. The model is based on the observations recorded from experimentation. These experiments are performed to understand the behaviour of debonding driving force with the variation in interface roughness and coating thickness.

Modelling of metal-coating delamination incorporating variable environmental parameters

A mathematical model for metal-coating delamination of degrading metal was developed incorporating multiple variable environmental and physical parameters. Metal-coating delamination not only depends on the electrochemical reactions at metal-coating interface but also on the factors like the type of propagating metal ions and their varying concentration with annual weather changes (summer and winter), time of exposure of the coated objects, type of coated objects, i.e. stationary or mobile vehicles and 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 (controlled and uncontrolled) using stochastic approach, effect of seasonal changes (summer and winter) on ionic compounds 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-coating delamination process and the ways to regress the under coating metal corrosion.

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.

Material Characterization and Real-Time Wear Evaluation of Pistons and Cylinder Liners of the Tiger 131 Military Tank

Material characterization and wear evaluation of the original and replacement pistons and cylinder liners from a Tiger 131 are reported. The original piston and cylinder liner were operative in the Tiger engine during WWII. The replacement piston and cylinder liner were used as substitutes and were obtained after failure in 2 h of operation in the actual engine. Material characterization revealed that the original piston was aluminum silicon hypereutectic alloy approximately matching the specification of RSA-419 AE, with a silicon content of 19.92 wt%. The replacement piston was aluminum copper alloy with a low silicon content of 0.73 wt%, approximately satisfying specifications of Al 2031 and Al 2618-T6. Scuffing, material removal, and ploughing were observed in the replacement piston and cylinder liner. These failures were attributed to inadequate piston material and design. The replacement piston average surface roughness was 9.09 μm and for the replacement cylinder liner it was 5.78 μm. Characterization results showed that both the original and replacement cylinder liners consisted of mostly iron, which is indicative of cast iron, a common material for this application.

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.

Corrosion Damage Analysis and Material Characterization of Sherman and Centaur—The Historic Military Tanks

A study of corrosion damage and material characterization of two historic military tanks, the Sherman and Centaur is reported. Experiments were conducted to analyse surface corrosion and corrosion propagation from surface to sub-surface. Significant surface corrosion was found, and this phenomenon was further facilitated by delamination failure mechanisms. Corrosion depth for the Sherman was approximately 110 μm, where sulphide inclusions were detected in the sub-surface analysis. The Centaurs analysis showed corrosion pits at 100 μm depth. These pits possess random geometrical configurations with evidence of sulphur, sodium, and calcium.

Water-Lubricated Ni-Based Composite (Ni–Al2O3, Ni–SiC and Ni–ZrO2) Thin Film Coatings for Industrial Applications

In this work, pure nickel and Ni-based nanocomposite coatings (Ni–Al2O3, Ni–SiC and Ni–ZrO2) were produced on steel substrate by using pulse electrodeposition technique. The industrial performance tests were conducted to evaluate the wear resistance, corrosion resistance, adhesion strength and wettability behaviour of newly developed coatings. Rolling contact ball-on-disc tribometer was used to assess anti-wear behaviour of these coatings under water-lubricated contacts. The results showed that the wear- and corrosion resistance properties of nickel alumina and Ni–SiC composite coatings significantly improved than that of pure Ni and Ni–ZrO2 coatings. The adhesion and wettability results of Ni–Al2O3 composite showed better performance when compared to the rest of the coatings. The effects of incorporating nanoparticles on the surface microstructure, interface adhesion and distribution of the particles were also investigated. The coatings were characterized by using scanning electron microscopy, X-ray diffraction analysis and 3D white light interferometry. The wear failure behaviour of these coatings was further examined by post-test surface observation under optical microscope.

Effect of bath ionic strength on adhesion and tribological properties of pure nickel and Ni-based nanocomposite coatings

Abstract The effect of electrolytic chemical concentration on wear-resistance, corrosion-resistance, adhesion and wettability properties of pure nickel and nickel–alumina composite coatings has been investigated in this paper. Coatings were electroplated over steel substrates under constant pulse conditions using pulse electrodeposition technique. Corrosion-resistance results show that the anti-corrosion properties are increasing with medium concentration (MC) both for pure nickel and nickel–alumina composite coating. For anti-wear properties, the MC showed increasing trend in case of pure nickel coatings but decreased in nickel–alumina composite coatings. In composite coating, the higher and low concentrations of electrolyte showed the higher wear resistance properties. Furthermore, the influence of electrolyte concentration on changing surface morphologies, mechanical, wettability and adhesion properties have been investigated and reported here. Surface morphologies of the synthesized coatings were studied with scanning electron microscopy (SEM) and energy-dispersive spectroscopy. Coatings surface mapping and wear analyses were examined by using 3D white light interferometry.

The Implications of Wet and Dry Turning on the Surface Quality of EN8 Steel

This paper, by experimental and investigation, examines the effects of dry and flood cutting conditions by comparing the rate of tool wear during metal turning and the produced surface roughness to determine if dry cutting can be a cost effective solution. For efficient manufacturing, the surface roughness of the turned parts should be dependent on their intended application, factors such as environment of operation or further manufacturing processes will determine this level of surface roughness required, as the performance and mechanical properties of the material can be affected. EN8 steel has been selected as the work material for its popularity and low hardness. The results show both wet and dry conditions have their benefits in relation to the intended application of the part, but mostly dry turning produces competitive surface roughness when finished by turning when compared to wet, and acceptable levels of tool wear while rough cutting. It would be recommended that in most circumstance for rough cutting, dry conditions should be employed with the knowledge of slight increased tool wear and possibly shorter life but with reduced manufacturing costs and environmental hazards.

Modeling the Effect of Residual and Diffusion-Induced Stresses on Corrosion at the Interface of Coating and Substrate

The effect of residual and diffusion-induced stresses on corrosion at the interface of coating and substrate has been analyzed within a multidisciplinary approach, i.e., material science, solid mec...