Delamination Of Coatings Research Articles

(Invited) Smart-Release Inhibition of Corrosion-Driven Organic Coating Delamination on Galvanized Steel Surfaces

In-coating cation and anion-exchange pigments are studied with respect to their ability to inhibit corrosion-driven organic coating disbondment on the zinc surface of hot-dip galvanized (HDG) steel. The efficiency of inorganic smart-release cation-exchangers, including bentonite and zeolite based pigments containing stored Zn(ii) inhibitor are compared with an organic cation-exchange cross-linked polystyrene based system. In-situ scanning Kelvin probe experiments carried out on HDG samples coated pigment-containing model polymer organic films showed that only the bentonite system was capable of halting delamination over a 24 h holding period, despite having a cation exchange capacity of only one third of the other exchangers. The reasons for this are discussed in terms of the kinetics of underfilm ion-exchange process. A preliminary investigation of anion-exchange hydrotalcite-based pigments is also described. The inhibition efficiency is shown to be highly anion specific, with chromate and phosphate exchanged pigments providing the best protection against organic coating cathodic disbondment.

Retrospective lifetime estimation of failed and explanted diamond-like carbon coated hip joint balls

Diamond-like carbon (DLC) coatings are known to have extremely low wear in many technical applications. The application of DLC as a coating has aimed at lowering wear and to preventing wear particle-induced osteolysis in artificial hip joints. In a medical study femoral heads coated with diamond-like amorphous carbon, a subgroup of DLC, articulating against polyethylene cups were implanted between 1993 and 1995. Within 8.5years about half of the hip joints had to be revised due to aseptic loosening. The explanted femoral heads showed many spots of local coating delamination. Several of these explanted coated TiAlV femoral heads have been analyzed to investigate the reason for this failure. Raman analysis and X-ray photoelectron spectroscopy (XPS) depth profiling showed that the coating consists of diamond-like amorphous carbon, several Si-doped layers and an adhesion-promoting Si interlayer. Focused ion beam (FIB) transverse cuts revealed that the delamination of the coatings is caused by in vivo corrosion of the Si interlayer. Using a delamination test set-up dissolution of the silicon adhesion-promoting interlayer at a speed of more than 100μmyear−1 was measured in vitro in solutions containing proteins. Although proteins are not directly involved in the corrosion reactions, they can block existing small cracks and crevices under the coating, hindering the exchange of liquid. This results in a build-up of crevice corrosion conditions in the crack, causing a slow dissolution of the Si interlayer.

A functionally gradient nano-Ni–Co/SiC composite coating on aluminum and its tribological properties

Functionally graded (FG) nano-structured Ni–Co/SiC coating was electrodeposited on an aluminum substrate. The mechanical properties of this coating compared with those of uniform Ni–Co/SiC and FG Ni/SiC coatings. The crystallographic texture and surface morphology of the coatings were studied by means of X-ray diffraction (XRD) and scanning electron microscope (SEM), respectively. Hardness, adhesion strength and wear resistance of coatings were also measured. The results indicated that FG Ni–Co/SiC coating showed lower friction coefficient and wear rate than FG Ni/SiC. It was due to the role of cobalt in refining microstructure and increasing SiC content into coating. In addition, FG Ni–Co/SiC coatings exhibited higher adhesion strength and wear resistance compared to those of the uniform coatings. Under wear load FG Ni–Co/SiC coating showed excellent wear resistance while uniform coatings failed due to large wear loss or delamination of coatings from substrate.

Smart-Release Inhibition of Corrosion-Driven Organic Coating Delamination on Galvanized Steel Surfaces

not Available.

Delamination of Ceramic Coatings with Embedded Metal Layers

This paper investigates the effects of thin plastically deformable layers embedded in an elastic coating upon debonding of a multilayer from its substrate. Such coatings are normally deposited at high temperature and cooled to ambient, resulting in significant stresses from thermal expansion mismatch. Other stresses can develop during subsequent thermal cycling if volumetric changes such as phase changes or oxidation occur in the system. We present an elastic–plastic model to calculate these stresses in the adhered state (after deposition and cooling but before debonding) and the released state (after delamination). These results are used to calculate the steady‐state energy release rate (ERR) that drives debonding at the interface between the multilayer and the substrate. It is shown that plastic straining in the ductile layers can lead to significant reductions in crack driving force by dissipating energy both before and during coating release. Regime maps are developed to illustrate reductions in ERR in terms of the yield strength and volume fraction of the metal layers. As an example, the model is used to predict the impact of embedded platinum layers within an yttria‐stabilized zirconica coating; the crack ERR for the composite coating is shown to be 30% lower than that for a uniform ceramic coating.

Effect of Spinel Growth on the Delamination of Thermal Barrier Coatings

The spinel growth induces undulation of the thermal growth oxide layer and decreases the service life of plasma-sprayed thermal barrier coatings. An analytical model is introduced to investigate the effect of spinel growth on the delamination of thermal barrier coating. The analytical results show that the number per unit area and the growth rate of spinel have significant influence on the delamination of thermal barrier coating. The stiffer and thicker thermal barrier coating is more easily to delaminate from the bond coat due to the existence of spinels. The effect of spinel on the delamination cannot be neglected. How to reduce the growth rate and the number of spinel is a key problem to prolong the service life of thermal barrier coatings.

Manufacturing of surface microstructures for improved tribological efficiency of powertrain components and forming tools

The performance and energy efficiency of mechanical components is strongly influenced by the tribological behaviour of their surfaces. This paper investigates the design and manufacturing of microstructured surfaces for improved wear resistance of forming tools and reduced friction in powertrain components. The potential of microstructures in the improvement of adhesion strength and resistance to delamination of hard coatings under the severe thermomechanical service conditions of hot forging tool surfaces is discussed. In the case of powertrain components, the ability of surface structures to reduce friction between lubricated bearing surfaces was investigated numerically and experimentally. The COMSOL Multiphysics Computational Fluid Dynamics (CFD) package was used to estimate the effect of geometric parameters of patterned spherical-segment cavities on hydrodynamic pressure. Electrochemical Machining by closed-electrolytic-free Jet (Jet-ECM) was used to manufacture the microstructures. Tribological ring-on-disc tests with structured surfaces were performed. It was determined that surface microstructures in the form of patterned spherical-segment cavities generate additional lift pressure which allows the surfaces to reach hydrodynamic lubrication at lower operating speeds.

A Dugdale model based geometrical amplifier enables the measurement of separation-to-failure for a cohesive interface

Regardless of all kinds of different formulae used for the traction-separation relationship in cohesive zone modeling, the peak traction σm and the separation-to-failure δ0 (or equivalently the work-to-separation Γ) are the primary parameters which control the interfacial fracture behaviors. Experimentally, it is hard to determine those quantities, especially for δ0, which occurs in a very localized region with possibly complicated geometries by material failure. Based on the Dugdale model, we show that the separation-to-failure of an interface could be amplified by a factor of L/rp in a typical peeling test, where L is the beam length and rp is the cohesive zone size. Such an amplifier makes δ0 feasible to be probed quantitatively from a simple peeling test. The method proposed here may be of importance to understanding interfacial fractures of layered structures, or in some nanoscale mechanical phenomena such as delamination of thin films and coatings.

Investigation of delamination mechanisms in polymer coatings by scanning acoustic microscopy

Scanning acoustic microscopy (SAM) was used to investigate disbonding, delamination and blister formation in polymer coatings for different layer structures and initial defect depths during exposure to a corrosive environment. The time evolution of disbonding and blister initiation and their growth was investigated by analysing the SAM images, taken after defined times of exposure to an electrolyte solution (Harrison solution).From investigations of a model system of coatings on steel substrates, it was possible to differentiate between water and/or ion transport (i) through the coating and (ii) along the coating–steel interface. For samples without clear coat randomly distributed blisters appeared at the coating–steel interface after exposure to the electrolyte solution, irrespective of the location of initial defects. The random distribution of growing blisters is related to diffusion of water and/or ions through the coating and ‘nucleation’ at weak points of the substrate or within the polymer. For samples with clear coat a propagating migration front along the coating–steel interface of 3–4 µm height—starting from initial defects—was detected. The linear propagation of this front cannot be explained by Fickian diffusion. Therefore, it is discussed in terms of an accelerated diffusion or crack growth kinetics. Since blistering starts only at sites, where the migration front has passed, the presence of a thin water layer at the coating–steel interface, the loss of adhesion and the following corrosive processes are prerequisites for the nucleation of blisters. The blister growth shows a square-root time dependence.

Influence of DLC coating thickness on tribological characteristics under sliding rolling contact condition

Diamond-like-carbon (DLC) coating of thickness 3 and 10 μm were developed with and without radical nitriding pretreatment on steel rollers and spur gear pair. The friction coefficient and wear amount were evaluated under sliding rolling contact condition in vacuum and under oil lubrication. Delamination of coatings was observed at the interface of the substrate. The wear resistance of coatings improved with the thickness of the coating. In vacuum both the roller and the gear pair of 10 μm coating thickness with radical nitriding showed identical wear behavior. The radical nitriding seemed to enhance the life of DLC coatings.

Coating delamination: Chink in the DES armor?

Catheterization and Cardiovascular InterventionsVolume 75, Issue 6 p. 912-913 Coronary Artery Disease Coating delamination: Chink in the DES armor?† Mark C. Bates MD, FACC, FSCAI, Corresponding Author Mark C. Bates MD, FACC, FSCAI [email protected] Professor of Medicine and Surgery, Co-Director CAMC Vascular Center of Excellence Charleston, West VirginiaVascular Center of Excellence, 3110 MacCorkle Avenue, Charleston, West VirginiaSearch for more papers by this author Mark C. Bates MD, FACC, FSCAI, Corresponding Author Mark C. Bates MD, FACC, FSCAI [email protected] Professor of Medicine and Surgery, Co-Director CAMC Vascular Center of Excellence Charleston, West VirginiaVascular Center of Excellence, 3110 MacCorkle Avenue, Charleston, West VirginiaSearch for more papers by this author First published: 23 April 2010 https://doi.org/10.1002/ccd.22580Citations: 1 † Conflict of interest: Dr. Bates is founder and shareholder in Nexeon MedSystems. Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL No abstract is available for this article.Citing Literature Volume75, Issue61 May 2010Pages 912-913 SCAI Member Sign in RelatedInformation

Cathodic delamination of seawater-immersed anticorrosive coatings: Mapping of parameters affecting the rate

Cathodic delamination is one of the major modes of failure for organic coatings immersed in seawater and refers to the weakening or loss of adhesion between the coating and the substrate. The diminished adhesion is the result of electrochemical reactions occurring at the coating–steel interface, where solid iron is oxidized to ferrous ions and oxygen is reduced to hydroxyl ions. In this work, the effects of various parameters on cathodic delamination have been investigated. The parameters are: permeability of the coating, concentration of dissolved oxygen and cations, polarization potential, type of binder, degree of curing, and pigment loading, shape and type. The results show that cathodic delamination increases with increasing concentration of cations up to the point where the concentration of dissolved oxygen becomes insufficient to maintain the corrosion rate. The rate of cathodic delamination is inversely proportional to the magnitude of polarization potential when ions can penetrate the coating, while cathodic polarization does not affect cathodic delamination when the ionic transport is restricted to the coating–steel interface. Increasing the pigment loading or partial replacement of spherical pigments with flake-shaped micaceous iron oxide or aluminium pigments reduces the rate of cathodic delamination. Finally, binders with an increasing amount of secondary hydroxyl groups in the polymer backbone reduce the rate of cathodic delamination while increasing the initial molar ratio of amide to epoxide increases cathodic delamination.

Discrimination Between Over-Thickness and Delamination of Thermal Barrier Coatings by Apparent Thermal Effusivity Thermographic Technique

When the delamination extent of thermal barrier coatings (TBC) is over a sufficiently large area to assess the adhesion of coatings, Pulse thermography (PT) is an effective technique, but often the distinction between delamination and TBC over-thickness is very difficult to determine. In this work, a recently developed algorithm based on apparent thermal effusivity has been applied to automatically distinguish between delamination and over-thickness during the inspection of a serviced gas turbine TBC-coated vane.

The influence of coating compliance on the delamination of thermal barrier coatings

Low relative density yttria stabilized zirconia (YSZ) thermal barrier coatings have been deposited on NiCoCrAlY over-lay bond-coated Hastelloy-X substrates by an electron beam-directed vapor deposition (EB-DVD) method. The coatings have been applied to both roughened and smooth bond coat surfaces. During thermal cycling, those deposited on roughened surfaces spalled by delamination with the failure located in the YSZ layer close to the thermally-grown oxide (TGO). The cracks were initiated at “corn kernel” defects in the YSZ layer by a bond coat rumpling mechanism. Coatings applied to smooth bond coat surfaces had much longer (factor of two) spallation lifetimes and delamination occurred at the bond coat/TGO interface by the nucleation and coalescence of interfacial voids. In both cases, the delamination lifetime decreased with coating density and significantly exceeded the lifetimes of higher density coatings made by conventional electron beam deposition methods. The enhanced life of the more porous coatings is consistent with an increased compliance. This reduces the YSZ layers stored strain energy contribution to the driving force for interface delamination.

Novel diol spiro orthocarbonates derived from glycerol as anti‐shrinkage additives for the cationic photopolymerization of epoxy monomers

AbstractShrinkage that takes place during polymerizations induces internal stress in polymeric materials generating a series of problems like poor adhesion to substrates and delamination in coatings or microcracks and microvoids in composites. Some additives like spiro orthocarbonates can reduce or eliminate this shrinkage. This paper deals with the synthesis of novel diol spiro orthocarbonates (DIOL SOCs) and their effect as anti‐shrinkage additives in the photopolymerization of the monomer 3,4‐epoxycyclohexyl‐3′, 4′‐epoxycyclohexanecarboxylate. It was found that increasing the concentration of the DIOL SOCs resulted in higher conversion of the monomer due to the presence of hydroxyl groups. The viscoelastic properties of the polymer products were also measured. It was observed that at 5 mol% of the mixture of DIOL SOCs there was an increase in the storage modulus due to the crosslinking produced by the bifunctional SOCs. However, at higher concentrations, a decrease in the storage modulus was observed. The level of shrinkage using the DIOL SOCs at 20 mol% was reduced by 45% when compared to the case without any additive. DIOL SOCs can be easily prepared by reacting glycerol with tetraethylorthocarbonate. These additives reduced significantly the level of shrinkage of the polyether derived from the diepoxycyclohexane monomer. Copyright © 2010 Society of Chemical Industry

Electrochemical impedance spectroscopy (EIS) study on corrosion performance of CrAlSiN coated steels in 3.5 wt.% NaCl solution

CrAlSiN coatings with Si contents from 0 to 11.5 at.% were deposited on AISI420 stainless and mild steels by magnetron sputtering. According to the broadened peaks in XRD patterns, an effect of grain refinement due to Si doping was verified in the as-deposited CrAlSiN coatings. Investigations by electrochemical impedance spectroscopy (EIS) were carried out in 3.5 wt.% NaCl solution, and the dependence of the nitride/steel configuration on the corrosion behavior was revealed in this study. Two different mechanisms were proposed for the CrAlSiN/AISI420 and CrAlSiN/MS configurations. For coated AISI420 samples, the CrAlSiN coatings revealed significant improvements on charge-transferred resistance ( R ct) with increasing Si content. These improvements were attributed to the dense microstructure of the CrAlSiN coatings. In contrast, CrAlSiN coatings deposited on mild steel substrates exhibited no specific trend on R ct in EIS tests. From the observation of the pitting holes, the lower R ct was attributed to serious delamination of the CrAlSiN coatings. In this case, the adhesion between coatings and mild steels was responsible for the measured R ct rather than the microstructure.

Mechanisms of Acute Angle Laser Drilling Induced Thermal Barrier Coating Delamination

Laser fabrication of cooling holes in certain parts of the aero-engine components involves percussion or trepan drilling at acute angles (e.g., 16–30 deg) to the surface. These parts are often covered with plasma sprayed ceramic thermal barrier coatings (TBCs) to protect them from reaching excessive temperatures in hot engine environments. Delamination of the TBC is the main problem of laser drilling acute angled holes in the coated components. The present study investigates the mechanisms involved in the development of the delamination cracks. A significant role of melt ejection in the formation of cracks and the delamination at the coating/coating interface of the leading edge of a laser-drilled inclined hole was identified. It is shown that the delamination mechanisms at the TBC coating/bond coating and the bond coating/substrate interfaces are different. Melt ejection induced stresses were identified as the key mechanisms for the former type, while the thermal effects dominates the latter type.

Delamination of thin coatings at scratching: experiments and numerics

Scratching of thin coatings on hard substrates is studied experimentally and numerically, in the latter case by use of the finite element method. In particular the delamination behaviour at scratching, by increasing the normal load up to failure, is of interest. The adhesion of the coating to the substrate is modelled as a cohesive zone where relevant model parameters are determined experimentally using the double cantilever beam test with uneven bending moments (DCB-UBM). Good correlation between experimental and numerical results were achieved and the most important finding confirms the fact that the delamination behaviour was very much dependent on the critical energy release rate of the film/substrate interface. The results achieved are directly relevant for thin film polymer coatings but can also be applied in more general situations as a comprehensive parameter study is performed using the finite element method.

Inhibition of Cathodic Coating Delamination on Zinc Electrocoated Steel Substrates by PVD Deposited Thin Aluminium Films.

not Available.

A photothermocapillary method for detecting delamination of paint and varnish coatings

The photothermocapillary (PTC) method proposed previously [9] for detecting near-surface inhomogeneities hidden under paint and varnish coatings is developed so as to also reveal defects in these coatings. We have measured the PTC response signal from the sites of coating delamination modeled as 1.4-mm-wide gaps formed by two (3 + 3 mm long) steps with the heights of 10, 20 and 20, 30 μm and as holes with diameters of 1.4 mm and depths of 0.5 and ∼2 mm in copper and duralumin plates, respectively. The results of experiments confirm the ability of the proposed PTC method to determine with good precision both the lateral dimensions of delamination regions and the heights of air gaps.