Roll coating is a vital industrial process used in printing,packaging,and polymer film production,where maintaining a uniform coating is critical for product quality and efficiency.This work models non-isothermal Carr...Roll coating is a vital industrial process used in printing,packaging,and polymer film production,where maintaining a uniform coating is critical for product quality and efficiency.This work models non-isothermal Carreau fluid flow between a rotating roll and a stationary wall under fixed boundary constraints to evaluate how non-Newtonian and thermal effects influence coating performance.The governing equations are transformed into non-dimensional form and simplified using lubrication approximation theory.Approximate analytical solutions are obtained via the perturbation technique,while numerical results are computed using both the finite difference method and the BVPMidrich technique.Furthermore,Response surface methodology(RSM)is employed for optimization and sensitivity analysis.Analytical and numerical results show strong agreement(<1%deviation).The model predicts coating thickness 0.55≤λ≤0.64,power input 1.05≤P_(w)≤1.99,and separation force 0.91≤S_(f)≤1.82 for 0.1≤We≤0.9 and 0.01≤F≤0.09.Increasing We enhances the coating thickness and power input but reduces velocity and separation force.The findings provide physical insight into elastic and viscous effects in roll coating,providing insight for optimizing coating uniformity,minimizing wear,improving industrial coating processes,and extending substrate lifespan.展开更多
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 cor...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.展开更多
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 a...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.展开更多
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 ...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.展开更多
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 ...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.展开更多
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 t...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.展开更多
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 th...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.展开更多
The lifespan of plasma-sprayed thermal barrier coating(TBC)systems is difficult to predict owing to the variety of microstructures and deterioration histories.In this study,we developed a novel TBC damage model to ref...The lifespan of plasma-sprayed thermal barrier coating(TBC)systems is difficult to predict owing to the variety of microstructures and deterioration histories.In this study,we developed a novel TBC damage model to reflect deterioration histories;thus,it can be applied to various TBCs.Damage to TBCs is classifed into oxidation and mechanical damage;therefore,a detailed deterioration history can be reflected.In addition,by introducing a virtual S–N diagram,a life prediction model that can be applied to TBCs with various microstructures was established.We used the proposed damage and life prediction models in isothermal aging and thermal cycle tests with different aging cycles.The predicted lifespan of TBCs by using the proposed models was within 95%of the results obtained by performing actual tests in the temperature range of 1150–1350℃.展开更多
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...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.展开更多
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 su...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.展开更多
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...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.展开更多
The failure mode and adhesion of thermal barrier coating (TBC) 8YSZ (ZrO2+8% (w/w) Y2O3) deposited on NiCoCrAlTaY bond coat by atmospheric plasma spraying were investigated. A grooved modified three-point bending spec...The failure mode and adhesion of thermal barrier coating (TBC) 8YSZ (ZrO2+8% (w/w) Y2O3) deposited on NiCoCrAlTaY bond coat by atmospheric plasma spraying were investigated. A grooved modified three-point bending specimen that can generate a single interface crack to facilitate the control of crack growth was adopted for testing, which was conducted at the ambient temperature of 100 °C. The morphology and composition of fractured surfaces were examined by means of a scanning electron microscopy (SEM) and an energy disperse spectroscopy (EDS). Images and spectrum show that cracks are initiated and propagated exclusively within YSZ layer adjacent to top/bond coat interface. The load-displacement curves obtained exhibit similar shapes that indicate two distinct stages in crack initiation and stable crack growth. Finite element analyses were performed to extract the adhesion strength of the TBCs. The delamination toughness of the plasma-sprayed 8YSZ coatings at 100 °C, in terms of critical strain energy release rate Gc, can be reliably obtained from an analytical solution.展开更多
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 ...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.展开更多
Thermal barrier coating(TBC)is crucial for the performance of turbine blades at high temperatures;however,it degrades the microstructure of single-crystal superalloy(SX),thereby reducing creep life.Despite this,the de...Thermal barrier coating(TBC)is crucial for the performance of turbine blades at high temperatures;however,it degrades the microstructure of single-crystal superalloy(SX),thereby reducing creep life.Despite this,the degradation mechanisms associated with the complex multi-layer damage and inter-layer diffusion behavior for TBC/SX systems have not yet been fully elucidated.In this study,using integrated experimental efforts and multiscale characterization techniques,the creep degradation mechanisms of TBC/SX systems at 900℃/500 MPa,980℃/300 MPa,and 1050℃/160 MPa are systematically investigated.Results demonstrate that the creep degradation from TBC intensifies with increasing temperature(T)and stress(σ)ratio(T/σ),exhibiting significant dependency on these two factors,and primarily reduces lifespan of the steady-state stage,with minimal effects on the accelerating stage.During creep deformation,the cracking behavior caused by thermally grown oxide(TGO)beneath the top coat(TC)layer,voids resulting from internal oxidation and interdiffusion in the bond coat(BC)layer,and the recrystallization growth driven by the sandblasting process in the secondary reaction zone(SRZ)are temperature-sensitive damages.In contrast,the initiation and propagation of cracks associated with the topologically close-packed(TCP)phases in the SRZ exhibit pronounced stress sensitivity.Furthermore,the formation of the substrate diffusion zone(SDZ)and the decomposition ofγ/γ′interfacial dislocation networks driven by the Cr-Ru diffusion,as well as the increased stacking fault energy in theγ′phase due to Co loss,are responsible for the acceleration of steady-state creep rate at 1050℃/160 MPa.This work provides a comprehensive and in-depth understanding of the degradation mechanisms under thermal-mechanical coupling in TBC/SX systems,offering new insights into targeted design optimization for multilayered coatings.展开更多
To mitigate the impact of interdiffusion reactions between the silicide slurry and Ta12W alloy substrate during vacuum sintering process on the oxidation resistance of the silicide coating,a micro-arc oxidation pretre...To mitigate the impact of interdiffusion reactions between the silicide slurry and Ta12W alloy substrate during vacuum sintering process on the oxidation resistance of the silicide coating,a micro-arc oxidation pretreatment was employed to construct a Ta_(2)O_(5)ceramic layer on the Ta12W alloy surface.Subsequently,a slurry spraying-vacuum sintering method was used to prepare a Si-Cr-Ti-Zr coating on the pretreated substrate.Comparative studies were conducted on the microstructure,phase composition,and isothermal oxidation resistance(at 1600℃)of the as-prepared coatings with and without the micro-arc oxidation ceramic layer.The results show that the Ta_(2)O_(5)layer prepared at 400 V is more continuous and has smaller pores than that prepared at 350 V.After microarc oxidation pretreatment,the Si-Cr-Ti-Zr coating on Ta12W alloy consists of three distinct layers:an upper layer dominated by Ti_(5)Si_(3),Ta_(5)Si_(3),and ZrSi;a middle layer dominated by TaSi_(2);a coating/substrate interfacial reaction layer dominated by Ta_(5)Si_(3).Both the Si-Cr-Ti-Zr coatings with and without the Ta_(2)O_(5)ceramic layer do not fail after isothermal oxidation at 1600℃for 5 h.Notably,the addition of the Ta2O5 ceramic layer reduces the high-temperature oxidation rate of the coating.展开更多
Black nickel coatings have emerged as a research hotspot in materials science due to their excellent performance and broad application prospects.In this study,nickel-based black coatings were fabricated on low-carbon ...Black nickel coatings have emerged as a research hotspot in materials science due to their excellent performance and broad application prospects.In this study,nickel-based black coatings were fabricated on low-carbon steel substrates via photo-assisted electrodeposition.A systematic investigation was conducted on the effects of cerium ion concentration and nano-ceria(CeO_(2))particle content in the electrolyte on the coating properties,along with an analysis of the temporal evolution of coating’s corrosion resistance.When the cerium ion concentration in the electrolyte was 0.05 mol/L,the coating exhibited a uniform black appearance with a light absorption rate of 95%,an emissivity of 0.87,maximum impedance,and the lowest corrosion tendency,demonstrating optimal comprehensive performance.The coating prepared with a nano-ceria concentration of 6 g/L in the electrolyte exhibited an emissivity of 0.9,achieved a 5B adhesion grade(ASTM D3359-09),and demonstrated a one-order-of-magnitude reduction in corrosion current density compared to coatings fabricated without nano-ceria in the electrolyte.With prolonged storage time,the coating's impedance slightly increased,leading to improved corrosion resistance.展开更多
The Sn−2Al filler metal was utilized to bond W90 tungsten heavy alloys by the ultrasonic-assisted coating technology in atmospheric environment at 250℃.The effects of ultrasonic power and ultrasonic time on microstru...The Sn−2Al filler metal was utilized to bond W90 tungsten heavy alloys by the ultrasonic-assisted coating technology in atmospheric environment at 250℃.The effects of ultrasonic power and ultrasonic time on microstructure and interfacial strength of Sn−2Al/W90 interface were investigated.The ultrasound improved the wettability of Sn−2Al filler metal on W90 surface.As the ultrasonic power increased and ultrasonic time increased,the size of Al phase in seam decreased.The maximum value of Sn−2Al/W90 interfacial strength reached 30.1 MPa.Based on the acoustic pressure simulation and bubble dynamics,the intensity of cavitation effect was proportional to ultrasonic power.The generated high temperature and high pressure by cavitation effect reached 83799.6 K and 1.26×10^(14) Pa,respectively.展开更多
TiB_(2)coatings can significantly enhance the high-temperature oxidation resistance of molybdenum,which would broaden the application range of molybdenum and alloys thereof.However,traditional methods for preparing Ti...TiB_(2)coatings can significantly enhance the high-temperature oxidation resistance of molybdenum,which would broaden the application range of molybdenum and alloys thereof.However,traditional methods for preparing TiB_(2)coatings have disadvantages such as high equipment costs,complicated processes,and highly toxic gas emissions.This paper proposes an environmentally friendly method,which requires inexpensive equipment and simple processing,for preparing TiB_(2)coating on molybdenum via electrophoretic deposition within Na3AlF6-based molten salts.The produced TiB_(2)layer had an approximate thickness of 60μm and exhibited high density,outstanding hardness(38.2 GPa)and robust adhesion strength(51 N).Additionally,high-temperature oxidation experiments revealed that,at900℃,the TiB_(2)coating provided effective protection to the molybdenum substrate against oxidation for 3 h.This result indicates that the TiB_(2)coating prepared on molybdenum using molten salt electrophoretic deposition possesses good high-temperature oxidation resistance.展开更多
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 ye...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.展开更多
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...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.展开更多
基金supported by the Talent Project of Tianchi Young-Doctoral Program in Xinjiang Uygur Autonomous Region of China(No.51052401510)Natural Science Foundation General Project(Grant Number 2025D01C36)of the Xinjiang Uyghur Autonomous Region of China+1 种基金This study received financial support from the National Natural Science Foundation of Xinjiang Province(Grant Nos.2022TSYCTD0019 and 2022D01D32)the China Scholarship Council(CSC)(Grant No.2021SLJ009915).
文摘Roll coating is a vital industrial process used in printing,packaging,and polymer film production,where maintaining a uniform coating is critical for product quality and efficiency.This work models non-isothermal Carreau fluid flow between a rotating roll and a stationary wall under fixed boundary constraints to evaluate how non-Newtonian and thermal effects influence coating performance.The governing equations are transformed into non-dimensional form and simplified using lubrication approximation theory.Approximate analytical solutions are obtained via the perturbation technique,while numerical results are computed using both the finite difference method and the BVPMidrich technique.Furthermore,Response surface methodology(RSM)is employed for optimization and sensitivity analysis.Analytical and numerical results show strong agreement(<1%deviation).The model predicts coating thickness 0.55≤λ≤0.64,power input 1.05≤P_(w)≤1.99,and separation force 0.91≤S_(f)≤1.82 for 0.1≤We≤0.9 and 0.01≤F≤0.09.Increasing We enhances the coating thickness and power input but reduces velocity and separation force.The findings provide physical insight into elastic and viscous effects in roll coating,providing insight for optimizing coating uniformity,minimizing wear,improving industrial coating processes,and extending substrate lifespan.
基金financially supported by the National Natural Science Foundation of China(No.51671198)。
文摘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.
基金Project supported by a grant from the Fundamental R&D Program for Core Technology of Materials funded by the Ministry of Knowledge Economy, KoreaProject (2010-0001-226) supported by NCRC(National Core Research Center) Program through the National Research Foundation of Korea funded by the Ministry of Education, Science and Technology
文摘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.
基金Supported by the Open Project of Key Laboratory of Marine New Materials of CNITECH(No.LMMT-KFKT-2014-008)the National Basic Research Program of China(973 Program)(No.2014CB643304)
文摘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.
基金financially supported by the National Natural Science Foundation of China(Nos.51173118,51273124 and51273126)the National Science Fund for Distinguished Young Scholars of China(No.51425305)+1 种基金the Youth Science and Technology Innovation Team of Sichuan Province(No.2015TD0001)State Key Laboratory of Polymer Materials Engineering(No.sklpme2014-2-03)
文摘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.
基金financed by Institutional Scholarship provided by Universiti Teknologi Malaysia and the Ministry of Higher Education of Malaysiathe Ministry of Higher Education of Malaysia and Universiti Teknologi Malaysia(UTM)for providing research facilities and financial support under the grant Q.J130000.2524.02H55
文摘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.
基金Project supported by the National Natural Science Foundation of China(No.51175404)
文摘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.
基金supported by the Korea Institute of Energy Technology Evaluation and Planning(KETEP)grant,funded by the Korean government(MOTIE)(No.20193310100030)the National Research Foundation of Korea(NRF)grant funded by the Korean government(MSIT)(No.2018R1A2A1A05077886)。
文摘The lifespan of plasma-sprayed thermal barrier coating(TBC)systems is difficult to predict owing to the variety of microstructures and deterioration histories.In this study,we developed a novel TBC damage model to reflect deterioration histories;thus,it can be applied to various TBCs.Damage to TBCs is classifed into oxidation and mechanical damage;therefore,a detailed deterioration history can be reflected.In addition,by introducing a virtual S–N diagram,a life prediction model that can be applied to TBCs with various microstructures was established.We used the proposed damage and life prediction models in isothermal aging and thermal cycle tests with different aging cycles.The predicted lifespan of TBCs by using the proposed models was within 95%of the results obtained by performing actual tests in the temperature range of 1150–1350℃.
基金This work was supported by the National Natural Science Foundation of China(Grant No.59971052).
文摘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.
文摘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.
基金Project supported by the National Natural Science Foundation of China(Grant No.51705533)the National Science and Technology Major Project of China(Grant No.2017-VII-0013-0110)+1 种基金the Fundamental Research Funds for the Central Universities,China(Grant No.2020YQJD17)the Tribology Science Fund of State Key Laboratory of Tribology(Grant No.SKLTKF18B15).
文摘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.
基金Project (No 2007CB707702) supported by the National Basic Research Program (973) of China
文摘The failure mode and adhesion of thermal barrier coating (TBC) 8YSZ (ZrO2+8% (w/w) Y2O3) deposited on NiCoCrAlTaY bond coat by atmospheric plasma spraying were investigated. A grooved modified three-point bending specimen that can generate a single interface crack to facilitate the control of crack growth was adopted for testing, which was conducted at the ambient temperature of 100 °C. The morphology and composition of fractured surfaces were examined by means of a scanning electron microscopy (SEM) and an energy disperse spectroscopy (EDS). Images and spectrum show that cracks are initiated and propagated exclusively within YSZ layer adjacent to top/bond coat interface. The load-displacement curves obtained exhibit similar shapes that indicate two distinct stages in crack initiation and stable crack growth. Finite element analyses were performed to extract the adhesion strength of the TBCs. The delamination toughness of the plasma-sprayed 8YSZ coatings at 100 °C, in terms of critical strain energy release rate Gc, can be reliably obtained from an analytical solution.
文摘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.
基金supported by the National Science and Technology Major Project of China(No.J2019-Ⅲ-0008-0051)the National Natural Science Foundation of China(Nos.52201140,52375225,and 92360307)the Natural Science Foundation for Youths of Shaanxi Province(No.2023-JC-QN-0521).
文摘Thermal barrier coating(TBC)is crucial for the performance of turbine blades at high temperatures;however,it degrades the microstructure of single-crystal superalloy(SX),thereby reducing creep life.Despite this,the degradation mechanisms associated with the complex multi-layer damage and inter-layer diffusion behavior for TBC/SX systems have not yet been fully elucidated.In this study,using integrated experimental efforts and multiscale characterization techniques,the creep degradation mechanisms of TBC/SX systems at 900℃/500 MPa,980℃/300 MPa,and 1050℃/160 MPa are systematically investigated.Results demonstrate that the creep degradation from TBC intensifies with increasing temperature(T)and stress(σ)ratio(T/σ),exhibiting significant dependency on these two factors,and primarily reduces lifespan of the steady-state stage,with minimal effects on the accelerating stage.During creep deformation,the cracking behavior caused by thermally grown oxide(TGO)beneath the top coat(TC)layer,voids resulting from internal oxidation and interdiffusion in the bond coat(BC)layer,and the recrystallization growth driven by the sandblasting process in the secondary reaction zone(SRZ)are temperature-sensitive damages.In contrast,the initiation and propagation of cracks associated with the topologically close-packed(TCP)phases in the SRZ exhibit pronounced stress sensitivity.Furthermore,the formation of the substrate diffusion zone(SDZ)and the decomposition ofγ/γ′interfacial dislocation networks driven by the Cr-Ru diffusion,as well as the increased stacking fault energy in theγ′phase due to Co loss,are responsible for the acceleration of steady-state creep rate at 1050℃/160 MPa.This work provides a comprehensive and in-depth understanding of the degradation mechanisms under thermal-mechanical coupling in TBC/SX systems,offering new insights into targeted design optimization for multilayered coatings.
基金National Natural Science Foundation of China(52071274)Key Research and Development Projects of Shaanxi Province(2023-YBGY-442)Science and Technology Nova Project-Innovative Talent Promotion Program of Shaanxi Province(2020KJXX-062)。
文摘To mitigate the impact of interdiffusion reactions between the silicide slurry and Ta12W alloy substrate during vacuum sintering process on the oxidation resistance of the silicide coating,a micro-arc oxidation pretreatment was employed to construct a Ta_(2)O_(5)ceramic layer on the Ta12W alloy surface.Subsequently,a slurry spraying-vacuum sintering method was used to prepare a Si-Cr-Ti-Zr coating on the pretreated substrate.Comparative studies were conducted on the microstructure,phase composition,and isothermal oxidation resistance(at 1600℃)of the as-prepared coatings with and without the micro-arc oxidation ceramic layer.The results show that the Ta_(2)O_(5)layer prepared at 400 V is more continuous and has smaller pores than that prepared at 350 V.After microarc oxidation pretreatment,the Si-Cr-Ti-Zr coating on Ta12W alloy consists of three distinct layers:an upper layer dominated by Ti_(5)Si_(3),Ta_(5)Si_(3),and ZrSi;a middle layer dominated by TaSi_(2);a coating/substrate interfacial reaction layer dominated by Ta_(5)Si_(3).Both the Si-Cr-Ti-Zr coatings with and without the Ta_(2)O_(5)ceramic layer do not fail after isothermal oxidation at 1600℃for 5 h.Notably,the addition of the Ta2O5 ceramic layer reduces the high-temperature oxidation rate of the coating.
文摘Black nickel coatings have emerged as a research hotspot in materials science due to their excellent performance and broad application prospects.In this study,nickel-based black coatings were fabricated on low-carbon steel substrates via photo-assisted electrodeposition.A systematic investigation was conducted on the effects of cerium ion concentration and nano-ceria(CeO_(2))particle content in the electrolyte on the coating properties,along with an analysis of the temporal evolution of coating’s corrosion resistance.When the cerium ion concentration in the electrolyte was 0.05 mol/L,the coating exhibited a uniform black appearance with a light absorption rate of 95%,an emissivity of 0.87,maximum impedance,and the lowest corrosion tendency,demonstrating optimal comprehensive performance.The coating prepared with a nano-ceria concentration of 6 g/L in the electrolyte exhibited an emissivity of 0.9,achieved a 5B adhesion grade(ASTM D3359-09),and demonstrated a one-order-of-magnitude reduction in corrosion current density compared to coatings fabricated without nano-ceria in the electrolyte.With prolonged storage time,the coating's impedance slightly increased,leading to improved corrosion resistance.
基金supported by the National Natural Science Foundation of China(Nos.52105330,52175307)the Natural Science Foundation of Shandong Province,China(No.ZR2023JQ021)。
文摘The Sn−2Al filler metal was utilized to bond W90 tungsten heavy alloys by the ultrasonic-assisted coating technology in atmospheric environment at 250℃.The effects of ultrasonic power and ultrasonic time on microstructure and interfacial strength of Sn−2Al/W90 interface were investigated.The ultrasound improved the wettability of Sn−2Al filler metal on W90 surface.As the ultrasonic power increased and ultrasonic time increased,the size of Al phase in seam decreased.The maximum value of Sn−2Al/W90 interfacial strength reached 30.1 MPa.Based on the acoustic pressure simulation and bubble dynamics,the intensity of cavitation effect was proportional to ultrasonic power.The generated high temperature and high pressure by cavitation effect reached 83799.6 K and 1.26×10^(14) Pa,respectively.
基金supported by the Original Exploratory Program of the National Natural Science Foundation of China(No.52450012)。
文摘TiB_(2)coatings can significantly enhance the high-temperature oxidation resistance of molybdenum,which would broaden the application range of molybdenum and alloys thereof.However,traditional methods for preparing TiB_(2)coatings have disadvantages such as high equipment costs,complicated processes,and highly toxic gas emissions.This paper proposes an environmentally friendly method,which requires inexpensive equipment and simple processing,for preparing TiB_(2)coating on molybdenum via electrophoretic deposition within Na3AlF6-based molten salts.The produced TiB_(2)layer had an approximate thickness of 60μm and exhibited high density,outstanding hardness(38.2 GPa)and robust adhesion strength(51 N).Additionally,high-temperature oxidation experiments revealed that,at900℃,the TiB_(2)coating provided effective protection to the molybdenum substrate against oxidation for 3 h.This result indicates that the TiB_(2)coating prepared on molybdenum using molten salt electrophoretic deposition possesses good high-temperature oxidation resistance.
文摘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.
基金supported by the National Natural Science Foundation of China(Grant Nos.11232008 and 11372118)the Tsinghua University Initiative Scientific Research Program
文摘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.
