Failure Mechanisms Of Coatings Research Articles

Oxidation behavior and failure mechanisms of enamel coatings at different temperature

This work studies the prolonged high-temperature oxidation behavior and failure mechanisms of enamel coatings at three distinct temperatures: 600 °C, 800 °C, and 1000 °C. The evolution of the coating’s microstructural morphology was characterized, and the kinematics of porosity, crystal precipitation, and oxide layer thickness were measured. The results indicated that at 600 °C and 800 °C, the coatings exhibit strong oxidation resistance and retain their mechanical integrity. However, at 1000 °C, the coatings rapidly deteriorate due to formation of Cr microcrystalline bands and the diffusion of oxidation layer, leading to volume expansion and element segregation. These factors result in the formation of voids and stress concentrations. The precipitation of crystals further exacerbates localized stress and microcracks, increasing the brittleness and enlarging the stress concentration areas, ultimately causing coating spallation. The effects of cooling rate on the long-term oxidation lifetime of the coatings were also examined. The findings of this work suggest that the temperatures below 800 °C are suitable for long-term application of the enamel coatings, while exposure to 1000 °C results in their rapid failure.

Oxygen concentration – A governing parameter for microstructural tailoring of duplex AlCrSiON coatings for superior mechanical, tribological, and anti-corrosion performance

This study investigates the impact of increasing oxygen levels on structure, and mechanical properties and tribological performance of duplex AlCrSiON coatings. AISI H13 steel and tungsten carbide substrates are coated using arc ion plating with increasing oxygen flow rate up to 200 sccm with varying oxygen concentration. High-resolution transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and three-dimensional profilometer are used to study morphological and structural evolution. Correspondingly, the coatings are assessed for hardness, adhesion strength, friction coefficient, and resistance against corrosion and wear. A 50–100 sccm oxygen flow rate is considered as an optimal range to receive lower surface roughness. Generally, the addition of oxygen has compromised hardness and friction coefficient but improve adhesion strength, wear and corrosion resistance with increasing oxygen concentration. The immersion tests have identified pitting corrosion as a dominating failure mechanism for AlCrSiON coatings when exposed to molten A380 aluminium alloy. This corrosion resistance stems from their dense microstructure, excellent thermal stability, and the presence of fcc-(Al, Cr)2O3 phase structure. This study demonstrates that controlled oxygen concentration is a crucial parameter for tuning the microstructure of AlCrSiON coatings to achieve superior mechanical, tribological, and anti-corrosion performance, particularly for high-pressure die-casting applications.

Structural evolution, wear and corrosion failure mechanisms of CrN coating synthesized by applying gradient voltage and arc-enhanced glow discharge

A detailed characterization was conducted to investigate the mechanical, wear and corrosion properties of CrN coatings deposited using a duplex technique combining gradient voltage (GV) and arc-enhanced glow discharge (AEGD). The absence of GV+AEGD resulted in the formation of large particles embedded in CrN coating, which adversely affected its toughness, density, and resistance to wear and corrosion. Remarkably, the implementation of GV+AEGD effectively mitigated particle agglomeration and promoted a compact growth texture in CrN coating. Consequently, besides exhibiting exceptional toughness and wear resistance, the CrN coating demonstrated outstanding corrosion resistance. The structural evolution, wear and corrosion failure mechanisms of CrN coatings with or without GV+AEGD were comprehensively discussed.

Failure mechanisms of interfacial coatings (MCrAlY+8YSZ) on high temperature solid particle erosion

Failure mechanisms of interfacial coatings (MCrAlY+8YSZ) on high temperature solid particle erosion

On the Thermal Shock Resistance and Failure Mechanism of the Pt-Modified Aluminide Bond Coating

The failure mechanism of the Pt-modified aluminide (Pt-Al) bond coating (β-(Ni, Pt)Al coating) in a simulated service environment has seldom been investigated. Based on a self-developed thermal barrier coating service environment simulator, a thermal shock experiment of single-phase Pt-Al bond coating on DD419 substrate at a temperature of 1170 °C was conducted combined with a real-time monitoring infrared thermal imager. The lifespan and failure mechanism of the coating are analyzed in detail. The results reveal that specimens of the Pt-Al bond coating, subjected to three repeated tests, exhibit failure after 650, 528, and 793 thermal shock cycles at 1170 °C, respectively. After failure, the contents of Pt and Al elements in the peeled region are lower than those in the unpeeled area, and a diffusion zone emerges in the bond coating. The failure mechanism of the Pt-Al bond coating during the thermal shock test can be attributed to three main aspects: (1) the diffusion and consumption of the Pt element reduced the oxidation resistance of the Pt-Al bond coating; (2) the diffusion and depletion of elemental Al causes a phase change in the coating, leading to the failure of the coating; (3) thermal stresses are generated in the Pt-Al bonded coating during the thermal shock test, which ultimately leads to wrinkling.

Applications of synchrotron-based X-ray diffraction in investigating thermal barrier coatings

Thermal barrier coatings play crucial roles in protecting the hot end components of aero-engines against high-temperature erosion. They must suffer extremely harsh environments including high temperatures, heavy loads, and large internal temperature gradients, which would result in various complex failures. Therefore, it is important to unveil these failure mechanisms to minimize and even prevent them for obvious reasons. Strain/stress evolution between different layers and foreign material erosion are the main failure mechanisms of thermal barrier coatings, which are well suited to be investigated using synchrotron X-ray diffraction. With its tunable energy, high flux, and many other advantages, synchrotron-based X-ray diffraction has become an advanced non-destructive characterization technique for engineering materials yielding important information including their compositions and residual stress which also provides spatial and temporal resolution that is vital for understanding their service performance. This paper presents a concise review of the applications of synchrotron-based X-ray diffraction in investigating thermal barrier coatings to explore their failure mechanisms.

RELATIONSHIP BETWEEN FATIGUE PROPERTIES AND CUTTING PERFORMANCES OF BILAYER TISIN/TIALN TOOL COATING

Impact test is a universal method to characterize the fatigue property of coated tools. For the bilayer TiSiN/TiAlN coated tool, the stress state in the cutting process with different feed rates were explored through cutting experiments. A high-temperature and high-frequency impact test platform was built. Through the impact tests with the introduction of the ‘pre-loading depth’, the fatigue properties and failure mechanisms of coatings under various test conditions were analyzed. Based on the comparative analysis of the results obtained in cutting experiments and impact tests, the mapping relationship between fatigue properties and cutting performances of the coatings was established, thus providing theory and practice foundation for characterization the cutting performance of coated tools under different cutting parameters by high-temperature and high-frequency impact tests.

Accelerated degradation of cathodic protected epoxy coating by Pseudomonas aeruginosa in seawater

The combination of coatings and cathodic protection (CP) is one of the most commonly used methods for corrosion protection of metal materials. However, the protection life of this method is difficult to match the original design, which mechanism is still not well known. Previous work reports that coatings experience degradation mainly due to cathodic disbondment and microbial factors in marine environments. To further explore the possible reason for this question, we studied the degradation behavior of epoxy coatings in the co-existence of CP and Pseudomonas aeruginosa in seawater using Electrochemical impedance spectroscopy (EIS), Confocal laser scanning microscope (CLSM), Scanning electron microscope (SEM), 3D microscopy, Fourier transform infrared spectroscopy (FTIR), Thermogravimetric analyzer (TGA), and Energy disperse spectrometer (EDS). The EIS results indicate that coating resistance drops bellows 106 Ω cm2 after 35 d of immersion under the effect of P. aeruginosa alone, but the degradation rate of coatings increases in the co-existence of CP and P. aeruginosa. The coating resistance drops bellows 106 Ω cm2 after 7 d of immersion in the P. aeruginosa containing seawater at − 1.05 VCSE. This may be due to P. aeruginosa can cause benzene ring removal from the epoxy coating, and the presence of CP promotes biofilm formation on the coating surface. The thickness of biofilm is about 33.3 μm at − 1.05 VCSE, which is about 1.5 times larger than at OCP, and the diameter of microscopic defects is about 9 times larger than in sterile seawater at the same CP potential. The presence of P. aeruginosa accelerate Cl− penetrating through the coating causing pitting corrosion of the substrate steel. This study revealed that the shorter protection life of organic coating can be attributed to the combined effect of CP and microorganisms in marine environments. The findings of this study can be referenced for better understanding of the coating failure mechanism in marine environments, and provide guidance for selecting appropriate organic coatings with anti-fouling and anti-corrosive properties.

Root causes for corrosion on painted steel structures in marine environments

AbstractOur understanding of the failure mechanisms of coatings, for example, cathodic disbonding, corrosion creep, blistering, and cracking, have been developed to a high level over the past decades. However, knowing what actually causes coatings to fail in the field is also important. Several atmospheric field tests of coating with duration 2–9 years have been published, showing that epoxy‐based heavy‐duty protective coating systems with zinc‐rich primers have high resistance against corrosion creep from damages in the coating. Despite this, scribe creep corrosion has become the most important evaluation parameter in standardized testing. In this work, inspection pictures from an offshore oil and gas platform, a ballast water tank system, and two coastal road bridges have been analyzed with respect to the root cause for initiation of corrosion on coated steel. The results show that corrosion mainly initiates at edges and welds. Between 50% and 90% of the corrosion attacks could be attributed to this, depending on the type of structure. The paint failed due to low film thickness, that is, the wet paint retracts from sharp edges in the surface so that the cured film has reduced barrier properties.

Prediction of multilayer Cr/GLC coatings degradation in deep-sea environments based on integrated mechanistic and machine learning models

Improving the accuracy of coating lifetime prediction on small sample data has been an urgent issue to be addressed. In this paper, based on in-situ electrochemical impedance spectroscopy data of multilayer Cr/GLC coatings, a lifetime prediction formula related to the coating failure mechanism is developed, which provides a quantitative basis for estimating the coating lifetime. Furthermore, the combination of the mechanistic prediction model and the ANN + RF integrated machine learning model can further increase the model’s prediction accuracy, reach 97.9%, and provide a new method for predicting coating performance and lifetime in deep-sea environments.

Mapping the coating failure modes of electroless plated metal on ABS polymer with micro-nano structured interface

Electroless plating is the default industrial process for depositing glossy metallic coatings on polymeric parts, most often made of acrylonitrile–butadiene–styrene (ABS) plastic. Unfortunately, the adhesion of plated metals on ABS requires harsh acid etching of the polymer, leaving hazardous chemical waste. We recently offered “Greener electrochemical plating of ABS polymer with unprecedented adhesion via hierarchical micro-nano texturing”. Understanding of the coating failure mechanism at the micro–nano structured interface would allow programming the adhesion strength via the topographical design of the interface. This study develops a theoretical map of coating failure modes versus geometrical parameters of the metal–polymer interface and validate via precise nanofabrication experiments. The ABS polymer was hot embossed with 2–6 μm wide, 2–6 μm deep micro-textures, then it was acid-etched for 1 min to superpose nano-texture over the micro-textures prior to the electroless Cu plating, coating peeling test, and microscopic characterization of the fractured interface. We observed four coating failure modes: (1) adhesive failure at interface, (2) mixed adhesive/cohesive failure, (3) cohesive failure of metal, and (4) cohesive failure of polymer; the last one demonstrated the highest peeling forces. Surprisingly, the proportionality of the adhesion force to the texture aspect ratio was valid only up to a certain threshold, beyond which the adhesion forces falls down due to the fail of metal. The results presented here allows one to control/program the adhesion strength at the metal-polymer interface and optimize the micro-texture of ABS parts for greener electroless plating and durable coating adhesion.

Synergistic acceleration effects of ultraviolet and salt spray on the degradation and failure of electromagnetic wave-absorbing coatings

There is an urgent need to reliably and rapidly evaluate the risk of failure of electromagnetic wave absorbing (EWA) coatings under the complex oceanic environment, which involves multiple weathering factors such as ultraviolet light, salt spray, etc. Unfortunately, conventional accelerated aging methods, which only consider single factor or apply multiple factors alternately, cannot adequately reproduce the failure modes and mechanisms of EWA coatings during real service. As a result, even though EWA coatings have passed existing qualification tests, their performance still could deteriorate much faster than expected. To this end, we investigated the synergistic acceleration effects of UV and salt spray on the degradation and failure of electromagnetic wave-absorbing coatings. Epoxy/flaky carbonyl iron (FCI) coating was prepared as the model sample. Effects of alternating- and combined-UV-salt spray (A-UV-SS and C-UV-SS) accelerated aging on the failure behaviors and underlying mechanisms of EWA coatings were investigated and compared thoroughly. It was found that EWA ability of coatings aged under C-UV-SS deteriorated much faster than that under A-UV-SS (more than two times). This additional acceleration aging effect was attributed to synergistic mechanisms with the coexistence of UV and salt spray: 1) acetic acid from the photo-oxidation of epoxy act synergistically with salt spray to accelerate the corrosion of Fe; 2) photovoltaic effect and salt spray synergistically promote the formation of iron oxides. This novel method has the potential to identify new failure mechanisms of EWA coatings and significantly reduce the test time, which is critical for their reliability evaluation and performance optimization.

Thermal shock behaviors and failure mechanisms of EB-PVD thermal barrier coatings using radiant heating

In this work, the thermal shock behaviors and failure mechanisms of the thermal barrier coatings (TBCs) were investigated with the self-built thermal shock platform. The results showed that the thermal shock cycles significantly could affect the microstructure and element distribution of TBCs. Firstly, the size of columnar gaps in the top coating (TC) layer increased with the increase of the thermal shock cycles. And, the transverse micro-cracks generated near the tip of the columnar gaps under the action of gradient stress. Moreover, Al elements in the bond coating (BC) significantly affected the growth mechanism of thermally grown oxide (TGO). The growth rate of the mixed oxide layer would be accelerated when the concentration of Al element in the BC layer dropped to a certain value. Finally, the accumulation of the thermal mismatch stress induced transverse cracks initiation and propagation in the porous mixed oxides layer, and the adhesion strength of TBCs decrease. When the transverse crack was connected with the columnar gaps, the TBCs would peeling off and failure at the interface of TC and TGO.

Hardened Enhancement Investigation of Al-Zr-N Coating by EBM Technique: A review

The purpose of this research is to examine the Al-Zr-N coating applied to the E19 steel alloy by physical vapour deposition using an electron beam. The physical vapour deposition processes used to create layered [Al-Zr-N] coatings and the structures, wear resistances, and corrosion behaviours of these materials. In order to examine the coating structures, surface roughness, micro-hardness, micro-abrasion, and pin on disc were used. One of the residual stress elements that can lead to failure mechanisms for suitable coatings is thermal stress. The mechanical characteristics of the coating, including its deposition temperature, young's modulus, thermal expansion coefficient, and substrate and coating thickness, were investigated using a validated computational simulation in this paper.

Compatibility of low thermal conductivity and high infrared emissivity of plasma-sprayed Sm2Hf2O7 and Pr2Hf2O7 coatings

In order to develop thermal-protection coatings, rare earth hafnates Sm2Hf2O7 (SHO) and Pr2Hf2O7 (PHO) coatings with pyrochlore structure were prepared on different substrates by atmospheric plasma spraying (APS). The infrared radiation, flame-ablation resistance, and thermal cycle performance were investigated in relationship with their morphologies, phase stabilities, thermophysical and mechanical properties. The results showed that both SHO and PHO coatings had compatible thermal-protection performance with lower thermal conductivity (0.711 and 0.779 W·m−1·K−1 at 1000 °C) and higher infrared emissivity (0.814 and 0.894 at 1000 °C) in the 3–5 μm band. Moreover, the supersonic flame ablation resistance of PHO coatings at high temperatures was greater than that of SHO coatings. Both SHO and PHO coatings have long thermal cycling life at low and medium temperatures and short thermal cycling life at high temperatures. The failure mechanisms of both type coatings were mainly associated with thermal expansion mismatch stress and fatigue stress generated during multiple thermal cycling.

A Review on Ceramic Matrix Composites and Environmental Barrier Coatings for Aero-Engine: Material Development and Failure Analysis

Ceramic matrix composites with environmental barrier coatings (CMC/EBCs) are the most promising material solution for hot section components of aero-engines. It is necessary to access relevant information and knowledge of the physical properties of various CMC and EBCs, the characteristics of defects and damages, and relevant failure mechanisms. Then, effective failure prediction models can be established. Individually assessing the failure of CMC and EBCs is not a simple task. Models considering the synergetic effect of coating properties and substrate fibrous architecture are more reasonable and more challenging. This paper offers a review and a detailed description of the materials features, failure mechanism, and failure modeling for both CMC substrate and EBC coatings. The various methods for failure analyses and their pros and cons are discussed. General remarks on technical development for failure modeling are summarized subsequently.

Microstructure, mechanical properties and tribological behaviors of (Co0.33Ni0.33Cr0.23Mo0.1)80−xNbx(B0.3Si0.7)20 high entropy amorphous alloy coatings

The (Co0.33Ni0.33Cr0.23Mo0.1)80−xNbx(B0.3Si0.7)20 high entropy amorphous alloy coatings (denoted as Nbx, x = 0, 2 and 4 at%) are successfully prepared by HVAF thermal spraying. The microstructure, mechanical properties and tribological behaviors of the as-sprayed coatings were comparatively investigated. The microstructure of as-sprayed coatings consists of amorphous phases, face-centered cubic (FCC) and (Cr, Mo)xB phases. Notably, the GFA (Glass-forming ability) of the as-sprayed coatings is improved and the precipitation of (Cr, Mo)xB phases is limited with the addition of Nb. The face-centered cubic (FCC) and (Cr, Mo)xB phases decrease with the Nb content increasing, and the Nb4 coating almost has a full amorphous structure. The Vickers hardness improves from 568.2 HV of Nb0 coating to 707.9 HV of Nb4 coating. The nanoindentation results indicate that the addition of Nb enhances the plastic deformation resistance and uniform deformation capacity of the coatings. For the as-sprayed coatings, the evolutions of tribological behaviors are consistent with the structural and mechanical variations. The addition of Nb decreases the oxidation wear and adhesion wear during friction process, which are the main wear failure mechanisms of as-sprayed coatings. The wear resistances of Nb4 coatings is increased by 49.54 % compared with that of the Nb0 coating, and the friction running-in time is decreased by 18.26 %.

Hydro-abrasive erosion behaviors of HVOF sprayed carbide-based cermet coatings in simulated seawater slurries

This paper aims at the hydro-abrasive erosion (HAE) behaviors in simulated seawater slurries under different flow velocities (FVs) and sand concentrations (SCs) of high-velocity oxygen-fuel (HVOF) sprayed carbide-based cermet coatings. The WC-Ni coating possessed worse anticorrosion property and superior HAE resistance regardless of FV and SC, and its HAE resistance was less affected by FV (80.6%) as well as SC (59.4%) in contrast with the Cr3C2-NiCr coating (141.4% and 103.8%) by taking the increment of VLR as the evaluation criteria. Higher FV and SC both contributed to the HAE degradation of the coatings, while FV had a greater effect on their HAE resistances than SC. The HAE failure mechanisms of both coatings under different FVs and SCs were also explained.

Thermal shock behaviour and failure mechanism of two-kind Cr coatings on non-planar structure

Cr coating is widely used as a protective coating on the inner and outer surface of industrial equipment. However, current researches on Cr coatings are predominantly conducted on plane specimens, and few works have considered the effect of irregular substrates on coatings. The thermal shock behaviour and failure mechanisms of two-kind Cr coatings prepared by electroplating and vacuum arc ion plating on non-planar structure at 900 °C were investigated. The microstructure and crystalline phases of the two-kind Cr coatings were analysed by scanning electron microscopy, energy dispersive spectrometry, and X-ray diffraction. The results indicate that vacuum arc ion plating Cr coating has better thermal shock resistance. There were two typical damaged regions for both Cr coatings, i.e.the concave corner of groove and the convex corner of land. By analysing the thermal shock damage behaviour of the coatings, it is concluded that fatigue stress, thermal mismatch stress, and the inherent properties of the two-kind Cr coatings are the main reasons for the difference in the overall damage degree, and the temperature stress concentration in the concave corner of groove is the cause for the higher degree of thermal shock damage.

Failure mechanisms of CrN and CrAlN coatings for solid particle erosion resistance

In this study, CrN and CrAlN coatings were deposited on the surface of aerospace titanium alloys using the arc ion plating technology to investigate the effect of the microstructure of the coatings on the mechanical and erosion resistance properties. The cross-sections of the coatings were observed by Scanning Electron Microscope(SEM), the microstructures were characterized by Transmission Electron Microscope(TEM), and the crystalline structures were tested by X-ray diffraction (XRD); furthermore, the hardness of the coatings was determined by a micro-Vickers hardness tester, the film-base bond strength was measured by a scratch tester, the change in curvature was measured by laser scanning and the residual stress was calculated. The fracture mechanism of the coating was elucidated by simulating the fracture pattern of the cross-section of the erosion crater. The results indicated that the thicknesses of the CrN and CrAlN coatings were almost the same, but the number of large particles on the surface of the CrAlN coating was higher. Both sets of coatings exhibited a nanocrystalline structure with a grain size of around 10 nm. Due to the doping of the Al element, the CrAlN coatings exhibited a hardness of 2846 HV and a higher residual stress of −1.831 GPa. Both the CrN and CrAlN coatings showed lower erosion rates than the titanium substrate at 30° and 90° angles of attack. The results of finite element simulations indicated that the more ductile CrN coating exhibited a better stress absorption capacity, and a typical brittle fracture failure mechanism was observed for both sets of coatings.