Alumina Coatings Research Articles

Nano Particles Effect on Transformation Behavior and Mechanical Properties on Commercial Steel Used for Automobile Parts

A scientific study has been performed in this research work on the basis of experimental results and ramification to divulge the advancement of second phase particles and its influence on ferrite and austenite phase transformation in less carbon-manganese added steel. Two steels have been engaged in this competition with and without aluminum addition along with nitrogen. To fade out the already present particles, as received steel under investigation was solution heat treated at 1200°C and then both the steel samples were heat treated at 750°C and 810°C for 15, 20, 35, and 70 sec incubation time in the cyanide added liquid bath furnace and were rapidly cooled from elevated temperature at room temperature in ordinary water. Metallography was performed after etching technique in two etchant solutions microstructural features with advanced Olympus optical microscope with polarized light. To further enlarge the important microstructure SEM was used to capture the micrographs. It was concluded that aluminum combine with nitrogen stimulate the fine aluminum nitride (AlN) particles and these particles were the major source to hinder the grain boundary mobility and consequently phase transformation was interrupted in aluminum added steel and it lowers the critical temperatures. Surprisingly there was no such attitude was observed in without aluminum added steel.

Densification and anticorrosion performances of vacuum evaporated aluminium coatings on NdFeB magnets

Al coated NdFeB magnets obtained by vacuum evaporation technique were densified by high energy ball milling method. The surface morphology, metal composition and microstructure of the coatings were characterized by scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy, respectively. The anticorrosive properties were investigated by potentiodynamic polarization curves and neutral salt spray test. The pores in the Al coatings of columnar crystals (Al) induced by the evaporation technique, were apparently filled in the following ball milling process, leading to the densification of Al coatings and the evident improvement of the anticorrosive performances. When treated with ball milling for 30 min, the sample achieves the best anticorrosive performances with the self-corrosion potential of −0.87 V, self-corrosion current density of 1.65 μA/cm2 and the neutral salt spray (NSS) time of 144 h (red rust). The improvement of the anticorrosive performances of vacuum evaporated Al coating mainly lies in the densification effect of the coating, which depends on different loading conditions of ball milling process.

Promoting Lithium Electrodeposition Towards the Bottom of 3-D Copper Meshes in Lithium-Based Batteries

Lithium (Li) has been considered as the promising negative electrode in rechargeable batteries, owing to the negative redox potential (-3.04 V vs. SHE), low density (0.534 g/cm3), and high theoretical specific capacity (3,860 mAh/g). However, the non-uniform stripping/plating process of the metallic Li is still challenging.[1] As one of the solutions, three-dimensional (3-D) metallic scaffolds were introduced to the negative electrode. The uniform electric field applied in the porous scaffolds could suppress the dendritic growth of the Li during the plating process. In addition, a decrease in the effective current density prolonged Sand’s time.[2] However, such a Li deposition mainly proceeded on the top surface and led to rapid surface clogging due to the strong surface electric field. In this presentation, we show the preferred Li deposition inside the 3-D copper (Cu) scaffold using gold nanoparticles (Au NPs). The lower Li nucleation energy barrier on the Au surface than that on the typical Cu current collector was investigated intensively.[3] However, the role of Au for spatially promoting Li deposition was not studied in depth. We added the Au NPs with an average particle size of ~7.5 nm to the bottom of 3-D Cu. The Au NPs with a total ~28 nmol reduced the charge-transfer resistance, which suggested the fast Li nucleation on the Au. In addition, we coated aluminum oxide (Al2O3) layer with ~ 26 nm of thickness on the top surface of 3-D Cu scaffold through the atomic layer deposition (ALD) process. This insulating layer further suppressed the Li deposition on the surface. As a result, apparent Li deposition towards the bottom of 3-D Cu was clearly demonstrated. During Li plating/stripping cycles, the surface clogging of the 3-D Cu/Au by an accumulation of solid electrolyte interphase (SEI) was also dramatically alleviated even in the absence of Al2O3 layer. It demonstrated the continuous Li deposition towards the bottom of the 3-D Cu/Au scaffold. Besides, symmetric 3-D Cu/Au cells exhibited over 95 % of Coulombic efficiency (CE) for ~120 cycles. The full cells comprised of the 3-D Cu/Au and LiFePO4 (LFP) electrodes delivered stable 300 cycles with a capacity of ~140 mAh/g at 1 C-rate. I will discuss the detailed role of the Au NPs and the Al2O3 layer, and comparative cell performances in the presentation.

Fabrication of Pt-Nanoparticle-Loaded Mesoporous Alumina Coating through Anodizing of an Al-Pt Alloy

Noble metal nanoparticles, usually dispersed in a mesoporous support, have widespread applications. However, uploading nanoparticles into mesoporous materials and preventing the nanoparticles from aggregation during the fabrication and application processes remain major challenges. Herein, we report a novel, simple and low-cost method for fabrication of Pt-nanoparticle-loaded mesoporous alumina coating through anodizing of an Al-Pt alloy (98.5 at% Al and 1.5 at% Pt) prepared by magnetron sputtering. It was found that the Al-Pt alloy could be effectively anodized at voltages between 2.8 and 4.5 V (SCE), in 0.4 M sulfuric acid solution, at room temperature. The anodizing processes resulted in Pt-nanoparticles of 5∼50 nm dimensions uniformly-dispersed in the porous anodic alumina film. The proposed method can be implemented on a large scale and extended to other alloy systems consisting of a valve metal and different alloying elements with Gibbs free energy of oxide formation less negative than that of the valve metal.

Evaluation on the Corrosion and Wear Properties of C-Fibers Doped Aluminum Coatings Obtained Using Arc Spray Technolgoy

Aiming at the wear and corrosion problems of fittings in 500-kV power transmission lines, a functional aluminum-based coating is prepared by an electric arc spraying process and self-made aluminum-based powder-cored wire. The experimental results showed that the friction coefficient of the coating is reduced from 0.4 to 0.2 after adding carbon fiber and that the wear rate is reduced from 2 × 10−3 to 8 × 10−4 mm3/(N·m). The electrochemical behavior of the composite coating is similar to that of the pure aluminum coating. After a 720-h salt spray test, there is no obvious corrosion products on the coating surface, and the thickness of the corrosion layer is only 29 μm. The new composite coating not only has a good anti-wear effect, but also maintains good corrosion resistance of the aluminum coating.

Characterization of multilayer coatings of aluminium, tungsten and molybdenum on steel substrate using laser-induced breakdown spectroscopy

Laser induced breakdown spectroscopy (LIBS) has been applied for the depth profiling of multilayer metallic coating structure which is simulated to the ITER-like wall materials in fusion devices such as EAST tokamak. The coatings were produced by magnetron sputtering and characterized by LIBS using a Nd:YAG laser at 1064 nm with pulse duration of 5 ns. The light from the resulting plasma was analyzed as a function of both number of laser pulse (N) and elemental spectral line intensity. The depth profile of the multilayer coating was determined by three different spectral signal processing methods; intensity background subtraction, intensity normalization and linear Pearson correlation. The intensity normalization method provides the best outcomes/solutions for thickness measurement and analysis of interfaces of multilayer coatings among other methods. The evolution of spectral intensity representing different materials was properly examined for 90 consecutive laser shots at the same spot. The ablation behaviour of the coating materials was analyzed in terms of ablation rate under the laser pulse of various fluences. In a much deep crater, some factors originating from laser ablation, such as material re-deposition and plasma shielding effect were analyzed. As a comparison, the depth, shape and diameter of craters were also measured using SEM and a profilometer. The influence of laser power density on the ablation rate and crater profile was investigated. The elemental composition, inside the crater, was verified by the EDX technique. The results indicate that LIBS has a potential power for in-situ depth profiling of multilayer coatings on the wall of the EAST.

Conformal Coating of Freestanding Particles by Vapor-Phase Infiltration.

A novel atomic layer method for encapsulating individual micro- and nano-particles with thin (sub-10-nm) dielectric films is presented. This method leverages the diffusion of vapor-phase precursors through an underlying inert polymer film to achieve growth of a metal oxide film on all sides of the particle simultaneously; even on the side that is in contact with the substrate. Crucially, the deposition is performed on stationary particles and does not require an agitation mechanism or a special reaction chamber. Here, conformal coatings of alumina are shown to improve stability in aqueous environments for two optically-relevant particles: compound semiconductor laser microparticles and lead halide perovskite nanocrystals.

Statistical Analysis of the Flexural Strength of Free-Standing Flame-Sprayed Alumina Coatings Prior and After Thermal Shock

The impact of thermal shock upon the scatter of flexural strength data of free-standing thin flame-sprayed Al2O3 coatings was examined. As published in the literature, thermally sprayed ceramic systems exhibit superior thermal shock resistance and against this background, the statistical evaluation of strength data prior and after the thermal shock was intensified. Thus, the Weibull parameters m and σ0 were compared before and after thermal shock from 1000 °C to room temperature. The flexural strength was determined utilising the ball-on-three-balls method. Although the general scale of the Weibull modulus m was rather low (< 6), considerable differences were shown after thermal shocking as the Weibull modulus decreased by a factor of about 3.

Alumina coating for dispersion management in ultra-high Q microresonators

Silica optical microspheres often exhibit ultra-high quality factors, yet their group velocity dispersion, which is crucial for nonlinear optics applications, can only be coarsely tuned. We experimentally demonstrate that group-velocity dispersion of a silica microsphere can be engineered by coating it with conformal nanometric layers of alumina yet preserving its ultra-high optical quality factors (∼107) at telecom wavelengths. Using the atomic layer deposition technique for the dielectric coating, which ensures nm-level thickness control, we not only achieve a fine dispersion tailoring but also maintain a low surface roughness and material absorption to ensure a low optical loss. Numerical simulations supporting our experimental results show that the alumina layer thickness is a promising technique for precise tuning of group-velocity dispersion. As an application, we demonstrate the generation of Kerr optical frequency combs, showing that the alumina coatings can also sustain the high optical intensities necessary for nonlinear optical phenomena.

Destruction electrospark deposits during Joule heating of base metal

Electrospark coating deposited on the surfaces of machine parts is a common surface hardening method. Hard materials are normally used for depositing to improve wear resistance or other properties. In this investigation electrospark deposition intended for use as micro-alloying of welds by deposition on to the surface of the base metal and in this case it remelts completely. Intense heating and destruction occurs before remelting, which changes the chemical composition of the melt. The aluminum and titanium coatings is shown to deteriorate at 500 to 650 °C generating a liquid phase due to eutectic available in both metals in this temperature range. Most of titanium and aluminum oxidized at that. It is found that a solid layer, appears after electrospark depositing using both coatings. For aluminum coating, after high-temperature heating, a thicker white layer appears with the same microhardness level as that of the base metal, and a thin layer of partial decarburizing. Fusion sectors are detected in the titanium coating that are harder than the base metal and have a dendritic structure, followed by a thin zone of complete decarburization and quite an extended zone of partial decarburization.

Surface modification of low carbon steel to improve corrosion resistance

Issues of improving the operational properties of low-carbon steels by coating are considered. It is shown that aluminum and chromium coatings increase the corrosion resistance of precision alloys without deterioration of their magnetic properties. It has been established that chromium coatings are more promising.

Comparison of Ordering Characteristics of Anodicformed Nanostructured Aluminum and Titanium Oxides Coatings

This article is concerned with the analysis of ordering the arrays of TiO2 and Al2O3 nanotubes using the correlation-spectral methods. As the tools, the spatial Fourier spectrum and one-dimensional autocorrelation function of SEM-image have served. It was shown that the arrays of the aluminum oxide nanotubes can have a nearly ideal ordering on a small scale at the expense of two-stage anodizing. It this case, the degree of order depends also on the purity of initial aluminum and sample preparation method. The introduced characteristics can serve as the measures of the structure order-disorder sensitive to both type and degree of order as a whole and to configuration of structural elements themselves.

Thick-Layer Nanostructured Electrospark Coatings of Aluminum and Its Alloys

It is shown that it is possible to obtain nanostructured layers with an increased thickness (up to 2 mm), suitable for the repair of worn surfaces of component parts made of aluminum alloys during electrospark alloying of the surface of the aluminum alloy (D1) by the processing electrode of an Al–Sn alloy (20% Sn) with the use of the high current density and two-phase technology for producing a multilayer coating (applying–melting).

Effect of Chlorella vulgaris Biofilm Adhesion on Electrochemical Behaviors of Wire Arc-Sprayed Aluminum Coatings

Thermal-sprayed aluminum (Al) coatings are widely used for corrosion protection in marine environments. The corrosive nature of seawater and the synergy with marine microbes make for aggressive service environments for Al coatings. In this study, Al coatings were deposited on 316L stainless steel (316L SS) substrates by using wire arc spraying. Chlorella vulgaris, a typical marine fouling algae, was used to investigate the effects of biofilm adhesion on the electrochemical behavior of wire arc-sprayed Al coatings in artificial seawater environment. Electrochemical measurements via dynamic potential polarization curves and electrochemical impedance spectroscopy were used to monitor the corrosion behavior after attachment of microbes on Al coatings and bare, uncoated 316L SS. Analysis of the corrosion products was conducted using scanning electron microscope and energy-dispersive spectrum. The results showed that the Chlorella vulgaris biofilm slowed the corrosion of the Al coatings. This suggested that Chlorella vulgaris biofilm was a critical contributing factor to the corrosion behavior of the Al coatings. Moreover, a mechanism was suggested to illustrate the corrosion behavior of Al coatings in the presence of Chlorella vulgaris.

Vibration and Corrosion Analysis of Modified Alumina Coating over Aluminum Alloy

This analysis is concerned with the investigation of the capability of alumina coating deposited by spray coating method using oxime-modified aluminum(III) isopropoxide as a sol–gel precursor to improve vibration damping and anti-corrosion properties of aluminum alloys. Coating microstructures, thickness and roughness were investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM) studies, respectively. To this end, the quality of the coating was determined by the corrosion rate which was analyzed by mean of electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. The vibration and noise technique were applied to measure comparison of vibration and noise damping of bare and alumina coated samples. The results indicate the alumina coating deposited over aluminum alloy by spray coating method is uniform, homogenous, crack free, having high vibration damping and anti-corrosive behavior.

Tribological Properties of Plasma Sprayed Alumina, Alumina-Titania and Alumina-Zirconia Coatings

Tribological Properties of Plasma Sprayed Alumina, Alumina-Titania and Alumina-Zirconia Coatings

Combustion of nitrate ester plasticized polyether propellants

Nitrate ester plasticized polyether (NEPE) is a kind of high-energy solid propellant that has both good mechanical properties and high specific impulse. However, its unique composition makes its combustion mechanism different from both double-base propellants and composite propellants. In order to study the combustion mechanism of NEPE propellants, we improved the free radical cracking model of previous research to make it capable of predicting the burning rate of NEPE propellants. To study the combustion characteristics and provide data support for the model, an experimental system was built and four kinds of NEPE propellants with different compositions and grain size distributions were tested. The results show that our modified model can reflect the combustion characteristics of NEPE propellants with an acceptable accuracy. The difference between the model and the experimental data is mainly caused by uncertain environmental factors and the ignorance of interactions between components. Both the experimental data and the results predicted by the model show that increasing the backpressure helps to increase the burning rate of NEPE propellants. Furthermore, the grain size of the oxidizer inside the NEPE propellant has a more severe impact on the burning rate but a lighter impact on the burning rate pressure exponent in comparison with the grain size of aluminum. For aluminum-free NEPE propellants, the reaction in the gas phase is dominant in the combustion process while adding aluminum into the propellant makes the solid phase dominant in the final stage. The combustion of fine aluminum particles near the burning surface generates heat feedback to the burning surface which evidently influences the surface temperature. However, the agglomeration of coarse aluminum particles has little effect on the burning surface temperature.

Influence of the Alumina Ceramic Coating on Friction and Stability of the Iron Contacts

Abstract The study focuses on monitoring influence of the alumina coatings on friction and stability of the microscale iron contacts by the smoothed particle hydrodynamics. The obtained results show a better stability and a higher value of the friction coefficient of the coated surface compared to those of the uncoated one. This study also supposes that in concern of stability of the surface the coating should be done with only the substrate surface accompanied with the roughness of the coating layer. The proportion of the coated particles is found to be strongly resulting in the friction properties, and the roughness of the coating layer also slightly results in those. The surface reaches the most stability at the proportion of around 70%.

Damping Behavior of Layered Aluminium and Aluminide Coatings on AISI 316 Austenitic Steel

Several coating configurations on AISI 316 steel were obtained by a hot dipping process followed by isothermal interdiffusion. Six different kind of multilayered specimens were produced and characterized. These coatings, typically employed as bond coat in thermal barrier coating (TBC), can also be effective as vibration reduction elements at intermediate and high temperatures. This preliminary work was focused on the microstructural design and processing effects of the coatings. The damping of the produced specimens was measured up to 450 °C and compared with that of the steel substrate. The most performing coatings contain an Al-Si layer and exhibit a steep damping increase above 200 °C, reasonably due to dislocation movements by plastic straining of soft alloy layer and to the interface sliding between layers with different elastic moduli.

Synergetic enhancement in the reactivity and stability of surface-oxide-free fine Al particles covered with a polytetrafluoroethylene nanolayer

Surface oxide (Al2O3) of reactive fine aluminum (Al) particles for solid fuels, propellants, and brazing materials often restricted oxidative performance, though the passivation film acts to protect Al particles from exploding. Here, we report fine Al particles fully covered with a polytetrafluoroethylene (PTFE) layer instead of an Al2O3 film on the surface. This advance is based on the introduction of strong Al–F bonds, known to be an alternative to the Al–O bonds of surface oxides. The DSC results on the PTFE-coated Al particles exhibit higher reactive-exothermic enthalpy energy (12.26 kJ g−1) than 4.85 kJ g−1 by uncoated Al particles. The artificial aging test of the PTFE layer on the Al particles show long-time stability to the external circumstance compared to those by Al2O3. The activation energy for oxidation was investigated from cyclic voltammetry assessment and the measured peak potentials of the anode curve for PTFE/Al (− 0.45 V) and uncoated Al (− 0.39 V) are achieved, respectively. This means that the PTFE layer is more stable against a sudden explosion of Al particles compared to Al2O3. These results are very useful given its capability to control both the reactivity and stability levels during the oxidation of Al particles for practical applications.