Influence of embedded particles on microstructure, corrosion resistance and thermal conductivity of CuO/SiO2 and NiO/SiO2 nanocomposite coatings

Homogeneous CuO/SiO₂ and NiO/SiO₂ nanocomposite coatings containing CuO and NiO nanoparticles in silica matrix were successfully synthesized by sol–gel process on an aluminum alloy substrate, respectively. The evolution of phase and morphology of both nanocomposites was characterized by XRD, SEM, TEM and FTIR. The effect of incorporating various nanoparticles on the corrosion behavior and the thermal conductivity of nanocomposite coatings was investigated by potentiodynamic polarization curve and comparative exponential method. The thermal conductivity as well as the corrosion resistance of nanocomposite coatings was significantly improved by the introduction of metal oxide particles. In comparison with NiO/SiO₂ nanocomposite coatings, CuO/SiO₂ composite coatings displayed lower protective behavior as well as higher thermal conductivity. Experimental results revealed that those improvements can directly be related to the nanocomposite effect and the nature of added nanoparticles.     

Finite element simulation of stress distribution and development in 8YSZ and double-ceramic-layer La2Zr2O7/8YSZ thermal barrier coatings during thermal shock

In this paper, the thermal stress of the double-ceramic-layer (DCL) La₂Zr₂O₇/8YSZ thermal barrier coatings (TBCs) fabricated by atmospheric plasma spraying (APS) during thermal shock has been calculated. The residual stress of the coating after being sprayed has been regarded as the initial condition of the first thermal cycle. The characteristic of the stress development during the thermal cycle has been discussed, and the influence of the defects on the failure mode during the thermal cycle has also been discussed systematically. Finite element simulation results show that there exist higher radial thermal shock stresses on the ceramic layer surface of these two coatings. There also exist higher thermal stress gradient at the interface between the ceramic layer and the metallic layer. Higher thermal stress in 8YSZ/NiCoCrAlY coating lead to the decrease of thermal shock property as compared to that of LZ/8YSZ/NiCoCrAlY coating. The addition of LZ ceramic layer can increase the insulation temperature, impede the oxygen transferring to the bond coating and can also reduce the thermal stress. Considering from the aspects of thermal insulation ability and the thermal shock resistance ability, DCL type LZ/8YSZ TBCs is a more promising coating material compared with the single-ceramic-layer (SCL) type 8YSZ TBCs for the application.     

激光重熔对等离子喷涂ZrO2-20%Y2O3热障涂层隔热性能的影响

采用大气等离子喷涂（APS）技术在铝基体表面制备氧化锆（ZrO2-20%Y2O3,质量分数）热障涂层,并用脉冲激光对其进行重熔处理,研究了激光重熔对涂层组织形貌、物相转变和隔热性能的影响。研究结果表明激光的比能量对涂层的成型及性能有重要影响,过高的比能量会使涂层表面粗糙度增加,涂层成型变差。在选用合适的低比能量激光重熔条件下,扫描电镜观察结果表明经激光重熔可消除喷涂态涂层的孔隙和层状结构。对粉末和重熔前后的涂层进行了X射线衍射分析,结果表明喷涂及重熔过程中都没有发生相变;隔热试验结果表明重熔后涂层的隔热温度有所下降。     

激光重熔对等离子喷涂ZrO_2-20%Y_2O_3热障涂层隔热性能的影响

采用大气等离子喷涂(APS)技术在铝基体表面制备氧化锆(ZrO2-20%Y2O3,质量分数)热障涂层,并用脉冲激光对其进行重熔处理,研究了激光重熔对涂层组织形貌、物相转变和隔热性能的影响。研究结果表明激光的比能量对涂层的成型及性能有重要影响,过高的比能量会使涂层表面粗糙度增加,涂层成型变差。在选用合适的低比能量激光重熔条件下,扫描电镜观察结果表明经激光重熔可消除喷涂态涂层的孔隙和层状结构。对粉末和重熔前后的涂层进行了X射线衍射分析,结果表明喷涂及重熔过程中都没有发生相变;隔热试验结果表明重熔后涂层的隔热温度有所下降。     

Influence of Co(CH3COO)2 concentration on thermal emissivity of coatings formed on titanium alloy by micro-arc oxidation

Ceramic thermal protection coatings on Ti6Al4V alloy were achieved by micro-arc oxidation (MAO) in the presence of Co(CH₃COO)₂. The morphology, crystallographic structure and chemical composition of the coating were characterized by various techniques. The thermal emission of the coating was measured by Fourier transform spectrometer apparatus. The bonding strength between the coating and substrate was studied, together with the thermal shock resistance of the coating. The results indicate that the content of Co in the coating layer significantly affects its thermal emissivity. Higher concentration of Co(CH₃COO)₂ in electrolytes leads to more Co ions into the coating, which enhances the emissivity of the coating. All the coatings show bonding strength higher than 10 MPa. In addition, the coating remains stable over 40 cycles of thermal shocking. The coating formed at 4 g/L Co(CH₃COO)₂ displays an average spectral emissivity value more than 0.9 and bonding strength about 10.4 MPa.     

Double-ceramic-layer thermal barrier coatings based on La2(Zr0.7Ce0.3)2O7/La2Ce2O7 deposited by electron beam-physical vapor deposition

Double-ceramic-layer (DCL) thermal barrier coatings (TBCs) of La₂(Zr_0.7Ce_0.3)₂O₇ (LZ7C3) and La₂Ce₂O₇ (LC) were deposited by electron beam-physical vapor deposition (EB-PVD). The composition, interdiffusion, surface and cross-sectional morphologies, cyclic oxidation behavior of DCL coating were studied. Energy dispersive spectroscopy and X-ray diffraction analyses indicate that both LZ7C3 and LC coatings are effectively fabricated by a single LZ7C3 ingot with properly controlling the deposition energy. The chemical compatibility of LC coating and thermally grown oxide (TGO) layer is unstable. LaAlO₃ is formed due to the chemical reaction between LC and Al₂O₃ which is the main composition of TGO layer. Additionally, the thermal cycling behavior of DCL coating is influenced by the interdiffusion of Zr and Ce between LZ7C3 and LC coatings. The failure of DCL coating is a result of the sintering of LZ7C3 coating surface, the chemical incompatibility of LC coating and TGO layer and the abnormal oxidation of bond coat. Since no single material that has been studied so far satisfies all the requirements for high temperature applications, DCL coating is an important development direction of TBCs.     

The effect of porosity on the laser induced damage threshold of TiO2 and ZrO2 single layer films

Monolayer ZrO₂ and TiO₂ films were prepared on BK7 glass by physical vapor deposition (PVD) and were subsequently annealed for 1 h at 300 °C. By using the transmission spectra of two samples and the envelope method, the refractive index dispersion and extinction coefficients have been calculated. Laser induced damage threshold (LIDT) measurement shows that despite slight differences between the extinction coefficients of the two samples, the LIDT parameter of the ZrO₂ film is greater than that of the TiO₂ film. This fact leads us to consider thermal conductivity as an important parameter for interpreting the LIDT difference. According to our theoretical analysis, as a consequence of increase in the number of thermal barriers along poorer film, its thermal conductivity, and hence LIDT, decreased, which is in agreement with our experimental results. The measured porosity of the two samples shows higher porosity for TiO₂ single layer, which is in agreement with atomic force (AFM) images. The gradual and smooth damage morphology of ZrO₂ observed in optical images implies higher thermal conductivity than TiO₂.     

Numerical study on the thermo-stress of ZrO2 thermal and barrier coatings by high-intensity pulsed ion beam irradiation

This paper studies numerically the thermo-mechanical effects of ZrO2 thermal barrier coatings (TBCs) irradiated by a high-intensity pulsed ion beam in consideration of the surface structure.Taking the deposited energy of ion beams in TBCs as the source term in the thermal conduction equation,the distribution of temperature in TBCs was simulated.Then,based on the distribution,the evolution of thermal stress was calculated by the finite element method.The results show that tensile radial stress formed at the valley of TBC surfaces after irradiation by HIPIB.Therefore,if cracks happen,they must be at valleys instead of peaks.As for the stress waves,no matter whether through peak or valley position,tensile and compressive stresses are present alternately inside TBCs along the depth direction,and the strength of stress decreases with time.     

Microstructure and mechanical properties of Al2O3-Al composite coatings deposited by plasma spraying

Al₂O₃ and Al₂O₃-Al composite coatings were prepared by plasma spraying. Phase composition of powders and as-sprayed coatings was determined by X-ray diffraction (XRD), while optical microscopy (OM) and scanning electron microscopy (SEM) were employed to investigate the morphology of impacted droplets, polished and fractured surface, and the element distribution in terms of wavelength-dispersive spectrometer (WDS). Mechanical properties including microhardness, adhesion and bending strength, fracture toughness and sliding wear rate were evaluated. The results indicated that the addition of Al into Al₂O₃ was beneficial to decrease the splashing of impinging droplets and to increase the deposition efficiency. The Al₂O₃-Al composite coating exhibited homogeneously dispersed pores and the co-sprayed Al particles were considered to be distributed in the splat boundary. Compared with Al₂O₃ coating, the composite coating showed slightly lower hardness, whereas the coexistence of metal Al phase and Al₂O₃ ceramic phase effectively improved the toughness, strength and wear resistance of coatings.     

Effect of spraying power on microstructure and bonding strength of MoSi2-based coatings prepared by supersonic plasma spraying

MoSi₂-based oxidation protective coatings for SiC-coated carbon/carbon composites were prepared using a supersonic plasma spraying at the power of 40 kW, 45 kW, 50 kW and 55 kW, respectively. Effect of spraying power on the microstructure and bonding strength of MoSi₂-based coatings was studied. The results show that coatings become more and more compact and the bonding strength increases when the spraying power increases from 40 kW to 50 kW. At the power of 50 kW, the coatings were dense and the bonding strength reached a maximum value of 14.5 MPa. As the spraying power is of sufficient magnitude, many cracks and pores reappaer in coatings and the bonding strength between coating and substrate also decreases.     

Influence of FeSO4 concentration on thermal emissivity of coatings formed on titanium alloy by micro-arc oxidation

Ceramic coatings with high emission were fabricated on Ti6Al4V alloy by microarc oxidation (MAO) with additive FeSO₄ into the electrolyte. The microstructure, chemical composition and chemical state of the coatings were determined by SEM, XRD, EDS and XPS, respectively. The bonding strength between the coating and substrate was studied by tensile strength test, together with the thermal shock resistance of the coating. The results showed that Fe content in the coating layer significantly affect its thermal emissivity. The relative content of Fe in the coatings surface increased at first and then decreased with increasing the concentration of FeSO₄ in electrolytes, so does the emissivity of the coatings. The bonding strength became weaker with increasing the concentration of FeSO₄. In addition, the coating remains stable over 40 cycles of thermal shocking. The coating formed at 3 g/L FeSO₄ demonstrates the highest an average spectral emissivity value around of 0.87, and bonding strength higher than 33 MPa.     

Preparation of nanocrystalline MnFe2O4 by doping with Ti ions using solid-state reaction route

Nanostructured manganese ferrites (MnFe₂O₄) with diameters in the range of 45–30 nm were synthesized by Ti⁴⁺ ion doping, using conventional solid-state reaction route. The substitution of Ti⁴⁺ ions created vacancies at Mn²⁺ sites and the coupling of ferrimagnetically active oxygen polyhedra was broken. This created nanoscale regions of ferrites. A reduction of magnetization for decreasing particle size was observed. Coercivity showed an increasing trend. This was explained as arising due to multidomain/monodomain magnetic behaviour of magnetic nanoparticles. DC resistivities of the doped specimens indicated the presence of an interfacial amorphous phase formed by the nanoparticles. Zero-field cooled and field-cooled curves from 30 nm sized particles showed a peak at T_B (∼125 K), typical of superparamagnetic blocking temperature.     

热聚合法制备纳米级Li3V2(PO4)3/C作为锂离子电池正极材料的性能研究

通过热聚合法成功制备出纳米级Li₃V₂（PO₄）₃/C正极材料,中间产物和最终材料的Li₃V₂（PO₄）₃/C颗粒均小于200 nm,无定形碳的含量为4.6%,处于Li₃V₂（PO₄）₃颗粒表面和颗粒与颗粒之间.该材料在3.0sim4.3 V和0.1 C电流下放电比容量为124 mAh/g,100次循环之后无衰减,表现出较好的循环性能.其倍率性能优异,在3.0sim4.3 V和20 C的条件下放电比容量达到80 mAh/g,在3.0sim4.8 V和10 C的条件下放电比容量达到100 mAh/g.     

Influences of laser remelting on microstructure of nanostructured Al2O3-13 wt.% TiO2 coatings fabricated by plasma spraying

The effects of laser remelting on microstructure of nanostructured Al₂O₃-13 wt.% TiO₂ ceramic coatings prepared by plasma spraying with agglomerated powders were studied. The microstructure of the feedstock, as-sprayed and laser-remelted coatings were investigated by using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffractometry (XRD). The results indicate that the plasma-sprayed ceramic coating consists of both fully melted regions and partially melted regions. The totally ceramic coating, especially the fully melted regions, has a typical plasma-sprayed lamellar-like structure as the conventional coating, and has some pores. According to the difference of microstructures, the partially melted regions can be divided into liquid-phase sintered regions (a three-dimensional net or skeleton-like structure: Al₂O₃-rich submicron particles embedded in the TiO₂-rich matrix) and solid-phase sintered regions (remained nanoparticles). The lamellar defect of the as-sprayed coating is erased, and the compactness of the coating is improved significantly after laser remelting. The laser-remelted region composed of fine equiaxed grains, which are different from the conventional column-like crystals along the direction of the heat current. Due to the rapid solidification of laser remelting process, there are still some nanoparticles in the remelted region because of an insufficient time for grains growth.     

Vanadium-Al2O3 nanostructured thin films prepared by pulsed laser deposition: Optical switching

The formation and optical response of VO_x nanoparticles embedded in amorphous aluminium oxide (Al₂O₃) thin films by pulsed laser deposition is studied. The thin films have been grown by alternate laser ablation of V and Al₂O₃ targets, which has resulted in a multilayer structure with embedded nanoparticles. The V content has been varied by changing the number of pulses on the V target. It is found that VO_x nanoparticles with dimensions around 5 nm have been formed. The structural analysis shows that the vanadium nanoparticles are oxidized, although probably there is not a unique oxide phase for each sample. The films show a different optical response depending on their vanadium content. Optical switching as a function of temperature has been observed for the two films with the highest vanadium content, at transition temperatures of about −20 °C and 315 °C thus suggesting the presence of nanoparticles with compositions V₄O₇ and V₂O₅, respectively.     

Stabilization of a very high-k crystalline ZrO2 phase by post deposition annealing of atomic layer deposited ZrO2/La2O3 dielectrics on germanium

The impact of the ZrO₂/La₂O₃ film thickness ratio and the post deposition annealing in the temperature range between 400 °C and 600 °C on the electrical properties of ultrathin ZrO₂/La₂O₃ high-k dielectrics grown by atomic layer deposition on (1 0 0) germanium is investigated. As-deposited stacks have a relative dielectric constant of 24 which is increased to a value of 35 after annealing at 500 °C due to the stabilization of tetragonal/cubic ZrO₂ phases. This effect depends on the absolute thickness of ZrO₂ within the dielectric stack and is limited due to possible interfacial reactions at the oxide/Ge interface. We show that adequate processing leads to very high-k dielectrics with EOT values below 1 nm, leakage current densities in the range of 0.01 A/cm², and interface trap densities in the range of 2-5 × 10¹² eV⁻¹ cm⁻².     

Optimization of annealing conditions of In2S3 thin films deposited by vacuum thermal evaporation

In₂S₃ thin films were grown on glass substrates by means of the vacuum thermal evaporation technique and subsequently thermally annealed in nitrogen and free air atmosphere from 250 to 350 °C for different durations. Experimental parameters have been adjusted in order to optimize the annealing conditions, and to obtain high band gap energy at low deposition temperature, as required for photovoltaic applications. In order to improve our understanding of the influence of the deposition and annealing parameters on device performance, we have investigated our indium sulfide material by X-ray diffraction, energy dispersive X-ray analysis (EDAX), atomic force microscopy (AFM) and spectrophotometry. The optical and structural properties of the films were studied as a function of the annealing temperature and durations. X-ray diffraction analysis shows the initial amorphous nature of deposited In-S thin films and the phase transition into crystalline In₂S₃ upon thermal annealing. Films show a good homogeneity and optical direct band gap energy about 2.2 eV. An annealing temperature of 350 °C during 60 min in air atmosphere were the optimal conditions.     

High resolution surface imaging of Co/ZrO2 catalyst by TOF-SIMS

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) is a useful tool for the characterization of supported catalyst. Especially, the possibility of surface imaging appears very interesting. The images of not only elements distribution but also molecules or their fragments may be performed. Owing to the fast improvement of time-of-flight secondary ions mass spectrometers, obtaining the surface images with lateral resolution even below 100 nm is possible. The application of TOF-SIMS to the high resolution surface imaging of catalysts surfaces was shown. The influence of the preparation conditions of Co/ZrO₂ catalyst on the dispersion and composition of the active phase was investigated. The Co⁺/Zr⁺ and CoOH⁺/Zr⁺ intensity ratio values were calculated.     

SHS等离子喷涂制备FeAl2O4-Al2O3-Fe纳米复合涂层的研究

利用SHS等离子喷涂技术，将经过机械团聚法制备的Fe₂O₃-Al复合粉体送入等离子焰流，沉积出厚度约为400 μm的复合涂层.利用XRD，SEM 和TEM等检测手段对涂层的成分和组织进行了分析，测定了涂层的显微硬度、断裂韧性以及耐磨性.结果表明涂层为具有纳米结构的FeAl₂O₄-Al₂O₃-Fe纳米复合组织；涂层的显微硬度为HV_100g870；断裂韧性是普通Al₂O₃涂层的2倍；无润滑磨损的耐磨性是普通Al₂O₃涂层的2.5倍. 关键词： SHS等离子喷涂 纳米涂层 断裂韧性     

Laser surface remelting of plasma sprayed nanostructured Al2O3-13wt%TiO2 coatings on titanium alloy

Plasma sprayed nanostructured coatings were successfully fabricated on a titanium alloy (Ti-6Al-4V) substrate using the as-prepared nanostructured Al₂O₃-13wt%TiO₂ feedstock. A CO₂ laser was used to remelt the plasma sprayed coatings. The effects of laser remelting on the phase constituents, microstructure and properties of the ceramic coatings were investigated. The laser remelted coatings (LRmC) possessed a much denser and more homogenous structure and excellent metallurgical bonding to the substrate. The average porosity of the LRmC was reduced to 0.9%, compared with 6.2% of the as-sprayed coatings. The net-like structure in the as-prepared feedstock remained in the coatings before and after laser remelting. The metastable γ-Al₂O₃ phase in the as-sprayed coatings transformed to stable α-Al₂O₃ during laser remelting. The LRmC could remain nanostructure. The microhardness of the coatings was enhanced to 1000-1400 HV_0.3 after laser remelting, which was much higher than that of the plasma sprayed coatings and 2-3 times higher that of the substrate. Significant decreases in surface roughness were also found in the LRmC.