Effect of carbon on microstructure of CrAlC_xN_(1-x) coatings by hybrid coating system

A systematic investigation of the microstructure of CrA1CxN1-x coatings as a function of carbon contents was conducted. Quaternary CrA1CxN1-x coatings were deposited on Si wafers by a hybrid coating system combining an arc-ion plating technique and a DC reactive magnetron sputtering technique using Cr and AI targets in the Ar/N2/CH4 gaseous mixture. The effect of carbon content on microstructure of CrA1C^N~ x coatings was investigated with instrumental analyses of X-ray diffraction, X-ray photoelectron, and high-resolution transmission electron microscopy. The results show that the carbon content of CrA1CxN1-x coatings linearly increases with increasing CH4/（CH4/N2） gas flow rate ratio. The surface roughness of the CrA1CxN1-x coating layer decreases with the increase of carbon content.

Evaluation of long-term corrosion durability and self-healing ability of scratched coating systems on carbon steel in a marine environment

Defects in protective-coating systems on steel surfaces are inevitable in practical engineering applications. A composite coating system, including a primer, middle coat and topcoat, were used to protect carbon steel from corrosion in a marine environment. Two environmental additives, glass fibers and thiourea, were applied in the middle coat to modify the coating system. The long-term corrosion durability and self-healing ability of the scratched coating system were evaluated by multiple methods. Results of the electrochemical technologies indicated that the coating system that contained 0.5 wt.% fibers and 0.5 wt.% thiourea presented good corrosion protection and self-healing for carbon steel when immersed in 3.5% NaCl for 120 d. Evolution of localized corrosion factors with time, as obtained from the current distribution showed that fibers combined with thiourea could inhibit the occurrence of local corrosion in scratched coating systems and retarded the corrosion development significantly. Surface characterization suggested that adequate thiourea could be absorbed tmiformly on fibers for a long time to play an important role in protecting the carbon steel. Finally, schematic models were established to demonstrate the action of fibers and thiourea on the exposed surface of the carbon steel and the scratched coating system in the entire deterioration process.

Investigation on behavior of crack penetration/deflection at interfaces in intelligent coating system

Based on the three-phase model, the propagation behavior of a matrix crack in an intelligent coating system is investigated by an energy criterion. The effect of the elastic mismatch parameters and the thickness of the interface layer on the ratio of the energy release rate for infinitesimal deflected and penetrated crack is evaluated with the finite element method. The results show that the ratio of the energy release rates strongly depends on the elastic mismatch al between the substrate and the driving layer. It also strongly depends on the elastic mismatch a2 between the driving layer and the sensing layer for a thinner driving layer when a primary crack reaches an interface between the substrate and the driving layer. Moreover, with the increase in the thickness of the driving layer, the dependence on a2 gradually decreases. The experimental observation on aluminum alloys monitored with intelligent coating shows that the established model can better explain the behavior of matrix crack penetration and can be used in optimization design of intelligent coating.

Improvement of thermally grown oxide layer in thermal barrier coating systems with nano alumina as third layer

A thermally grown oxide （TGO） layer is formed at the interface of bond coat/top coat. The TGO growth during thermal exposure in air plays an important role in the spallation of the ceramic layer from the bond coat. High temperature oxidation resistance of four types of atmospheric plasma sprayed TBCs was investigated. These coatings were oxidized at 1000 °C for 24, 48 and 120 h in a normal electric furnace under air atmosphere. Microstructural characterization showed that the growth of the TGO layer in nano NiCrAlY/YSZ/nano Al2O3 coating is much lower than in other coatings. Moreover, EDS and XRD analyses revealed the formation of Ni（Cr,Al）2O4 mixed oxides （as spinel） and NiO onto the Al2O3 （TGO） layer. The formation of detrimental mixed oxides （spinels） on the Al2O3 （TGO） layer of nano NiCrAlY/YSZ/nano Al2O3 coating is much lower compared to that of other coatings after 120 h of high temperature oxidation at 1000 °C.

Oxidation and Hot Corrosion Behavior of a Composite Coating System

The oxidation and hot corrosion behavior of Co-Ni-Cr-AI-Ta-Y coating produced by magnetron sputtering with and without enamel coating has been investigated in air at 900℃ and in molten 75 wt pct NaCl+25 wt pct Na2SO4 at 850℃. The results show that the enamel coating possesses good hot corrosion resistance in the molten salts, in comparison with the sputtered Co-Ni-Cr-AI-Ta-Y coating. In the hot corrosion test, breakaway corrosion did not occur on the samples with enamel coating and the composition of enamel coating did not significantly change either. The oxidation resistance of the sputtered coating, which offers good adhesion, can be improved by the enamel coating.

Thermal properties of glass-ceramic bonded thermal barrier coating system

The thermal properties of a thermal barrier coating （TBC） system comprised of BaO-MgO-SiO_2 based glass-ceramic bond coating, 8% （mass fraction） yttria stabilized zirconia （8YSZ） top coating and nimonic alloy substrate were evaluated. The thermal diffusivity and thermal conductivity of the TBC coated substrate were lower than those of bare substrate and glass-ceramic coated substrate under identical conditions. The specific heat capacity, thermal diffusivity and thermal conductivity of the TBC coated substrate increase with the increase of the temperature. Further, it is observed that the thermal conductivity of the TBC system decreases with the increase in the top coating thickness.

Weakening effect of plastic yielding inception in thin hard coating systems

Hard coatings have been widely applied to enhance tribological performance of mechanical components.However,it was predicted that thin hard coatings may have a weakening effect which could reduce the coating/substrate system’s resistance to plastic yielding compared with the uncoated substrate material.In this paper,analytical simulation is utilized to investigate the origin of weakening effect.The functions of material mechanical properties and coating thickness on the weakening effect are theoretically investigated.Partial-unloading spherical nanoindentation tests are performed on tungsten coated single crystalline silicon and copper to acquire the stress-strain curves and compared with the uncoated cases.The experimental results are in consistence with the analytical solutions,demonstrating the presence of weakening effect.

Rheological Behaviour, Synthesis and Performance of Smart Thermal Barrier Coating Systems Based on Hollow Alumina

The stability of three water-based slurries containing different loads of Al microparticles was measured by laser scattering. The slurries displayed a Newtonian behaviour and the evolution of viscosity over nine days was found to be constant. Ground surfaces of nickel were also wetted similarly irrespective of the Al content in the slurries (30, 40 or 50 wt%) thereby demonstrating that the 1/10 PVA/H2O water based slurries are adequate for spraying. After deposition and annealing of the as-sprayed coatings, a thermal barrier coating system was formed with a top coat of hollow alumina spheres, an intermediate thermally grown oxide and a bottom aluminized bond coat. The coating system is shown to display very low thermal conductivity and remarkable oxidation resistance at high temperatures.

EFFECT OF ARTIFICIAL WEATHERING AND TEMPERATURE CYCLING ON THE ADHESION STRENGTH OF WATERBORNE ACRYLATE COATING SYSTEMS USED FOR WOODEN WINDOWS

The adhesion of coatings to wood is important for their long-term performance.In this study,the adhesion strength of water-based acrylate coatings used for wooden windows after exposure to artificial weathering(AW)and temperature cycling(TC)was investigated.The analysis of the adhesion quality of coatings was performed via a pull-off test and failure characteristics.The 3-layered and 4-layered white and brown acrylate dispersions from six different producers were compared and the effect of coating thickness on adhesion strength was investigated.The adhesion strength values proved to be very variable.After AW,the adhesion strength and its variability increased for all the samples.TC had no statistically significant effect on the adhesion strength values.White coating systems were initially characterized by lower adhesion strength,but after AW and TC,they reached higher adhesion strength values than brown ones.The overall highest adhesion after AW and TC was recorded for the coatings based on alkyd-acrylate hybrid basis(Producer 3),while the lowest adhesion variability after AW was measured for one type of tested acrylate coating(Producer 4).The effect of different layering on adhesion strength was not demonstrated in this study.

Process and performance of DAAF microspheres prepared by continuous integration from synthesis to spherical coating based on microfluidic system

In order to improve the energy output consistency of 3, 3’-diamino-4, 4’-azoxyfurazan(DAAF) in the new insensitive booster and the safety and efficiency in the preparation process, a continuous preparation system of DAAF from synthesis to spherical coating was designed and established in this paper, which combined ultrasonic micromixing reaction with microdroplet globular template. In the rapid micromixing stage, the microfluidic mixing technology with ultrasonic was used to synergistically strengthen the uniform and rapid mass transfer mixing reaction between raw materials to ensure the uniformity of DAAF particle nucleation-growth, and to prepare high-quality DAAF crystals with uniform structure and morphology and concentrated particle size distribution. In the microdroplet globular template stage, the microfluidic droplet technology was used to form a droplet globular template with uniform size under the shear action of the continuous phase of the dispersed phase solution containing DAAF particles and binder. The size of the droplet template was controlled by adjusting the flow rate ratio between the continuous phase and the dispersed phase. In the droplet globular template, with the diffusion of the solvent in the dispersed phase droplets, the binder precipitates to coat the DAAF into a ball, forming a DAAF microsphere with high sphericity, narrow particle size distribution and good monodispersity. The problem of discontinuity and DAAF particle suspension in the process was solved, and the coating theory under this process was studied. DAAF was coated with different binder formulations of fluororubber(F2604), nitrocellulose(NC) and NC/glycidyl azide polymer(GAP), and the process verification and evaluation of the system were carried out. The balling effects of large, medium and small droplet templates under different binder formulations were studied. The scanning electron microscope(SEM) results show that the three droplet templates under the three binder formulations exhibit good balling effect and narrow particle size distribution. The DAAF microspheres were characterized by powder X-ray diffraction(XRD), differential scanning calorimetry(DSC), thermo-gravimetric(TG) and sensitivity analyzer. The results showed that the crystal structure of DAAF did not change during the process, and the prepared DAAF microspheres had lower decomposition temperature and lower mechanical sensitivity than raw DAAF. The results of detonation parameters show that the coating of DAAF by using the above three binder formulations will not greatly reduce the energy output of DAAF, and has comparable detonation performance to raw DAAF. This study proves an efficient and safe continuous system from synthesis to spherical coating modification of explosives, which provides a new way for the continuous, safe and efficient preparation of spherical explosives.

Assessing the corrosion protection property of coatings loaded with corrosion inhibitors using the real-time atmospheric corrosion monitoring technique

The atmospheric corrosion monitoring(ACM)technique has been widely employed to track the real-time corrosion behavior of metal materials.However,limited studies have applied ACM to the corrosion protection properties of organic coatings.This study compared a bare epoxy coating with one containing zinc phosphate corrosion inhibitors,both applied on ACM sensors,to observe their corrosion protection properties over time.Coatings with artificial damage via scratches were exposed to immersion and alternating dry and wet environments,which allowed for monitoring galvanic corrosion currents in real-time.Throughout the corrosion tests,the ACM currents of the zinc phosphate/epoxy coating were considerably lower than those of the blank epoxy coating.The trend in ACM current variations closely matched the results obtained from regular electrochemical tests and surface analysis.This alignment highlights the potential of the ACM technique in evaluating the corrosion protection capabilities of organic coatings.Compared with the blank epoxy coating,the zinc phosphate/epoxy coating showed much-decreased ACM current values that confirmed the effective inhibition of zinc phosphate against steel corrosion beneath the damaged coating.

Corrosion mechanism of CuAl-NiC abradable seal coating system——The influence of porosity,multiphase,and multilayer structure on the corrosion failure

In this study,the corrosion behavior of the CuAl-NiC abradable seal coating system in chloride solution was investigated to systematically research the effect of porosity,multiphase,and multilayer structure on the corrosion failure.Through the composition and structure analysis,the corrosion process of the system was predicted and then verified with mercury intrusion porosimetry,cross-section SEM/EDS analysis,and electrochemical measurements.The results demonstrated that the interphase selective corrosion caused the porosity of the top layer to decrease first and then increase during the corrosion development.The interlayer galvanic corrosion,determined by the pore connectivity,is crucial for corrosion failure.

Role of coatings and materials of external fixation pins on the rates of pin tract infection:A systematic review and meta-analysis

BACKGROUND Infection at the pin tract is a frequent and feared complication of external fixators(EF).The type of pin material and coatings have been regarded as possibly influencing infection rates.Over the last 20 years,few prospective clinical studies and systematic reviews addressed the role of coated pins on the rate of pin site infection in human clinical studies.AIM To assess the EF literature over the past 20 years on the clinical benefits of pins manufactured from varied materials and coating systems and their possible role in pin tract infection rates.METHODS We performed a systematic review according to the PRISMA and PICOS guidelines using four scientific platforms:PubMed,LiLacs,SciELO,and Cochrane.We searched the literature for related publications over the past 20 years.RESULTS A literature search yielded 29 articles,among which seven met the inclusion criteria.These studies compared stainless-steel pins and pins coated with hydroxyapatite(HA),titanium and silver.The pin tract infection definitions were arbitrary and not standardized among studies.Most studies included a low number of patients in the analysis and used a short follow-up time.Three metaanalyses were carried out,comparing stainless steel vs silver pins,stainless steel vs HA-coated pins,and titanium vs HA-coated pins.None of this analysis resulted in statistically significant differences in pin tract infection rates.CONCLUSION Currently,no clinical evidence supports the advantage of EF pins manufactured with materials other than stainless steel or coated over uncoated pins in reducing the rates of pin tract infections.A standardized definition of pin tract infection in external fixation is still lacking.

Simulation of residual stresses and their effects on thermal barrier coating systems using finite element method

Thermal barrier coating(TBC)systems are widely used in industrial gas-turbine engines.However,premature failures have impaired the use of TBCs and cut down their lifetime,which requires a better understanding of their failure mechanisms.In the present study,experimental studies of isothermal cycling are firstly carried out with the observation and estimation of microstructures.According to the experimental results,a finite element model is established for the analysis of stress perpendicular to the TBC/BC interface.Detailed residual stress distributions in TBC are obtained to reflect the influence of mechanical properties,oxidation,and interfacial roughness.The calculated results show that the maximum tensile stress concentration appears at the peak of TBC and continues to increase with thermal cycles.Because of the microstructural characteristics of plasma-sprayed TBCs,cracks initialize in tensile stress concentration(TSC)regions at the peaks of TBC and propagate along the TBC/BC interface resulting in the spallation of TBC.Also,the inclusion of creep is crucial to failure prediction and is more important than the inclusion of sintering in the simulation.

Preparation and Characterization of Controlled Heparin Release Waterborne Polyurethane Coating Systems

In this study, to improve hemocompatibility of biomedical materials, a waterborne polyurethane （WPU）haepafin release coating system （WPU/heparin） is fabricated via simply blending biodegradable WPU emulsions with heparin aqueous solutions. The surface compositions and hydrophilicity of these WPU/heparin blend coatings are characterized by attenuated total reflectance infrared spectroscopy （ATR-FTIR） and water contact angle measurements. These WPU/heparin blend coatings show effectively controlled release of heparin, as determined by the toluidine blue method. Furthermore, the biocompatibility and anticoagulant activity of these blend coatings are evaluated based on the protein adsorption, platelet adhesion, activated partial thromboplastin time （APTT）, thrombin time （TT）, hemolysis, and cytotoxicity. The results indicate that better hemocompatibility and cytocompatilibity are obtained due to blending heparin into this waterborne polyurethane. Thus, the WPU/heparin blend coating system is expected to be valuable for various biomedical applications.

Potential bioactive coating system for high-performance absorbable magnesium bone implants

Magnesium alloys are considered the most suitable absorbable metals for bone fracture fixation implants.The main challenge in absorbable magnesium alloys is their high corrosion/degradation rate that needs to be controlled.Various coatings have been applied to magnesium alloys to slow down their corrosion rates to match their corrosion rate to the regeneration rate of the bone fracture.In this review,a bioactive coating is proposed to slow down the corrosion rate of magnesium alloys and accelerate the bone fracture healing process.The main aim of the bioactive coatings is to enhance the direct attachment of living tissues and thereby facilitate osteoconduction.Hydroxyapatite,collagen type I,recombinant human bone morphogenetic proteins 2,simvastatin,zoledronate,and strontium are six bioactive agents that show high potential for developing a bioactive coating system for high-performance absorbable magnesium bone implants.In addition to coating,the substrate itself can be made bioactive by alloying magnesium with calcium,zinc,copper,and manganese that were found to promote bone regeneration.

Computerized three-dimensional design system for rectangular tile coating on hull surface

To better guide the coating process of rectangular tiles on a ship hull, a computerized three-dimensional design method is proposed. Research was done on a tile generating algorithm, tile laying design flow, tiles gap examination algorithm, and tiles slight displacement, as well as cutting and rotating algorithms.A three-dimensional design system was developed using an MDT platform. The application of this system indicates that using the design arrangement to coat tiles on a ship’s hull can result in enhanced coating quality.

Review of the fatigue behavior of hard coating–ductile substrate systems

With the wide application of coating materials in aerospace and other fields, their safety under fatigue conditions in service is important.However, research on the fatigue properties of ceramic hard coatings started late, and a unified standard is yet to be established to evaluate the fatigue life of hard coating–ductile substrate systems.Studies also present different opinions on whether coatings can improve or reduce the fatigue life of substrates.In this paper, the influence of the properties of ceramic coatings on fatigue performance is reviewed, and the effects of coating on the mechanism of fatigue crack initiation in substrates are discussed, aiming to help readers understand the fatigue behavior of hard coating–ductile substrate systems.

ISO/TR 20498-5 Traditional Chinese Medicine-Computerized tongue image analysis system-Part 5:Method of acquisition and expression of tongue colour and tongue coating colour

International Organization for Standardization(ISO)officially released ISO/TR 20498-5 Traditional Chinese medicine-Computerized tongue image analysis system--Part 5:Method of acquisition and expression of tongue colour and tongue coating colour on January 11,2019.ISO/TR 20498-5 was formulated by the team of Professor Wang Yiqin,from School of Basic Medicine of Shanghai University of TCM and Shanghai Key Laboratory of Health Identification and Evaluation,and jointly completed by East China University of Science and Technology and Suzhou Jingyu Medical Instrument Co.,LTD.

Experimental study and numerical modeling of the damage evolution of thermal barrier coating systems under tension

This study investigated the damage evolution(i.e., formation of vertical cracks, transformation of vertical cracks to interfacial crack and delamination) of thermal barrier coating systems under tension by using experimental and numerical methods.Experimental results revealed that the first transverse crack that was perpendicular to the load direction occurred when the strain of the top coat reached 0.5%. The full-scale strain of the top coat layer obtained by using the Digital Image Correlation technique indicated that surface cracks formed due to the coalescence of micro-cracks. Moreover, the results of the finite element method demonstrated that the vertical cracks initiated from the coating surface and extended through the thickness of the coatings. The density of the surface cracks was used as a damage evolution indicator such that numerical simulation could predict the cracking behaviour under tension loading. The results were consistent with those of the experimental study.