Al Al2O3 Research Articles

Wear rate and hardness characteristics of Al7075/kyanite (Al2SiO5) composites

In the present work kyanite (Al2SiO5) used as reinforcement material by varying weight-percentage of 2 wt%, 4 wt%, 6 wt% and 8 wt% in Al7075 alloy matrix material. Al7075-kyanite composites prepared using vortex method by stir casting technique. Microstructural studies of cast composites is carried out using optical microscopy and X-ray diffraction studies. XRD studies shows the peaks subsequent to Al, Al2SiO5 and minor Al2O3, SiO2 phases. Optical microscopy results the uniform distribution of kyanite in Al7075 matrix. The dry pin-on-disc unlubricated wear tests conducted to observe the wear behaviour of the Al7075-alloy and its casted composites. The dry sliding wear tests carried out at various sliding speeds (0.6, 0.8 and 1 m/s), sliding distances (250, 500, 750 and 1000 m) and loads (20, 40 and 60 N). It is contingent that, wear rate of Al-Al2SiO5 composite is lesser than unreinforced Al 7075 in all combination of sliding speeds, sliding distances and loads. The wear rate is decreases 9.9 × 10−4 ± 6.1 × 10−4 mm3/m increase in wt% of kyanite in matrix material and sliding speed. Wear rate is decreases 7.19 × 10−4 ± 1.71 × 10−4 mm3/m increasing sliding distance. Wear rate is increases 1.52 × 10−3 ± 0.3 × 10−3 mm3/m increasing load. Brinell hardness tested increases hardness with increase in wt% of kyanite in matrix. Worn surface analysis is carried out to analyze the effect of reinforcement on worn surfaces. Hardness is superior for Al7075/8 wt% kyanite composites. Composites gives higher hardness and wear resistance compared to Al7075 matrix.

Sol\u2013gel alumina coating on quartz substrate for environmental protection

Transparent γ-Al2O3 thin film can be utilized as an absorbent or protective layer in environmental protection. The aim of the present research work is to improve the structural and optical properties of γ-Al2O3 thin film. Al2O3 thin films were synthesized by various newly developed routes based on colloidal technique and sol–gel chemistry. Many types of starting materials (Al acetate, nitrate, isopropoxide, boehmite, and Al2O3 powders) and additives (acetic acid, HCl, HNO3, citric acid) were used in the experiments. Suspension and gel-like precursor systems were compared for layer creation. The layers were characterized by their morphology (GIXRD), surface and thickness (SEM), as well as transparency (UV–visible spectroscopy). The best quality of layer (∼90% transmittance, 50–60 nm thickness, perfect covering) has been obtained by sol–gel technique starting from Al nitrate or Al acetate.

Reversed Photoeffect in Transparent Graphene Nanocapacitors

Electronic properties of ultrathin dielectric films consistently attract much attention since they play important roles in various electronic devices, such as field effect transistors and memory elements. Insulating properties of the gate oxide in transistors represent the key factor limiting Moore’s law. The dielectric strength of the insulating film limits how much energy can be stored in nanocapacitors. The origin of the electric current in the nanometer-scale insulating barrier remains unexplained. Here we present an optically transparent Al–Al2O3–graphene nanocapacitor suitable for studying electronic transport in calibrated nanoscale dielectric films under high electric fields and with light exposure. The controllable flow of photons provides an additional powerful probe helping to resolve the puzzle of the electric conductivity in these high-quality insulating films. The dielectric alumina, Al2O3, is deposited by atomic layer deposition technology. With this device we observe a photon-assisted field emission effect, in which the effective barrier height is reduced by a quantity equal to the photon energy. Our main finding is a reversed photoeffect. Namely, at sufficiently high bias voltages the current through the dielectric film decreases as the light intensity increases. Moreover, higher photon energies correlate with stronger decreases of the current. To explain this reversed photoeffect, we present a qualitative model based on a conjecture that electrons leak into the dielectric and form charged sandpile-like branching patterns, which facilitate transport and which can be dispersed by light.

Comparison of Mechanical Properties and Corrosion Behavior of Al-NanoAl2O3 with Al-MicroAl2O3 Composites Made by SPS Process

In this research, spark plasma sintering (SPS) was used as a new method in the fabrication of Al–Al2O3 composites. The effect of Al2O3 particle size (both nano and micron) and its amount on the relative density, hardness, resistance, corrosion and compressive strength in Al–Al2O3 composite were investigated. Evaluation and size characterization of nano particle was carried out by transmission electron microscope. The distribution of particles throughout sample, as well as the detection of the elements in the structure were studied by scanning electron microscopy equipped by corresponding energy dispersive X-ray spectrometer analysis. According to the results, in the sample containing 3 wt% of nanoparticle of Al2O3, the mechanical properties of composite and corrosion resistance were improved due to uniform distribution of Al2O3 nanoparticles. However, by increasing weight percent or particle size of Al2O3 in composite, properties such as corrosion resistance and mechanical strength were considerably reduced. It can be attributed to the porosity and agglomeration of particle that were produced in composite.

Electrochemical synthesis of Al–Al2O3 composites for selective laser melting

Novel electrochemical method for obtaining Al–Al2O3 composites for selective laser melting technology has been studied. The electrochemical cell with the flexible cathode and the anode device has been developed. The initial aluminum powder was characterized: aluminum content was more than 99.8 wt %; the average particle diameter was ∼40 μm. Oxidized aluminum powder was studied: γ–Al2O3 in the surface oxide layer form was detected; the increase in the particle diameter was 10–20 μm. Electrochemical oxidation technological parameters have been studied. At 0.1 A cm−2 cathodic current density electrolysis duration was 220 min, 24 V voltage along with 80 ° C electrolyte temperature reached. The oxidation mechanism of aluminum particles has been developed. The increase in the surface oxide layer occurred, and this led to an increase in voltage. The 3D object from the oxidized aluminum powder was synthesized by selective laser melting method. The 3D object was perfectly sintered and did not crumble. Good reinforcements distribution in the volume of the synthesized 3D object has been achieved.

Comparison of interfacial and critical current behaviour of Al+Al2O3 sheathed MgB2 wires with Ta and Ti diffusion barriers

We present a comparative study of the interfacial reactions for the MgB2 wires with different diffusion barriers (Ta or Ti) and the outer (Al + Al2O3) sheath with variable Al purity and Al2O3 content. The reaction of (Al + Al2O3) with Ta produces non-uniform but considerably thinner interfacial layer than with Ti. The critical currents (Ic) of the MgB2 wires with Ta barrier do not vary any significantly for different heat treatment conditions, and in contrast, those with Ti barrier show a strong variation with Al purity and volume % of Al2O3 particles in the (Al + Al2O3) sheath. For the (Al + Al2O3) sheathed wire with Ti barrier, the maximum Ic is attained when the highest purity of 99.995% Al is used although the thickest reaction zone has developed at the Ti–(Al + Al2O3) interface. The critical current values suggest that not the interfacial reaction kinetics of barrier–sheath rather the purity of the Al powder and the volume % of Al2O3 particles in sheath determine the current carrying ability of the MgB2 composite wires. The current-voltage characteristics of wires when combined with the reaction behaviour at barrier–sheath interfaces, the (Al + Al2O3) sheathed MgB2 wires with Ti diffusion barrier looks more promising than Ta for engineering applications.

Highly Reactive Prestressed Aluminum under High Velocity Impact Loading: Processing for Improved Energy Conversion

Harnessing greater power from metal particle combustion requires engineering the core‐shell particle structure to more rapidly release stored chemical energy upon ignition. This study examines the metallurgical process of prestressing to increase the strain inside aluminum (Al) particles, then links increased strain to altered reaction mechanisms under high velocity impact. Results show that the quenching rate during prestressing changes the Al reaction mechanism. At faster quenching rates (900 K min−1), roughly 50% of the interfacial surface between the Al core and Al2O3 shell delaminates based on a model developed to understand the measured strain. Without core reinforcement, the shell fractures readily upon impact causing dramatically increased ignition sensitivity (measured in terms of pressurization rate) and reactivity (measured in terms of flame spreading). For slower quenching rates (200 K min−1), the core‐shell interface remains intact but strain in the particle increases by an order of magnitude. In addition, elastic stiffness in the shell may increase during prestressing. Increased elastic stiffness can effectively reduce ignition sensitivity and higher strain may contribute energy toward the nearly 40% increase in reactivity for the slower quenched aluminum powder. These results establish a link between altering mechanical properties of particles and their ignition and reactivity under dynamic loads.

Effect of Al2O3 nanoparticles content and compaction temperature on properties of Al–Al2O3 coated Cu nanocomposites

This paper presents experimental investigation on the effect of Al2O3 content and compaction temperature on mechanical and wear properties of Al–Al2O3 coated Cu nanocomposites. With the aim of improving wettability and dispersion of high weight fraction of Al2O3 nanoparticles in Al matrix, Al2O3 nanoparticles were electroless coated by Cu particles. High-energy ball milling followed by hot compaction was applied to manufacture Al–Al2O3 coated Cu nanocomposites. The results showed that increasing Al2O3 nanoparticles content up to 10 wt% improved hardness and wear properties of samples compacted at 400 ᵒC, while by increasing Al2O3 content to 15 wt%, the properties were negatively affected due to the agglomeration of Al2O3 nanoparticles and the high reduction of relative density. However, well dispersion of high content of Al2O3, 15 wt%, was achieved in samples compacted at 700 MPa which improved hardness by 105% compared to pure Al. The hot compaction temperature highly influenced structural, mechanical and wear properties of compacted samples. Increasing compaction temperature, reduced crystallite size (49 nm) and increased the relative density of Al–Al2O3 coated Cu nanocomposites which improved mechanical and wear properties of the produced samples. Applying electroless deposition of Cu over Al2O3 nanoparticles followed by high-energy ball milling and hot compaction at 700 MPa is an efficient procedure for production of Al–Al2O3 coated Cu nanocomposite with relatively high Al2O3 content.

Effect of nanoparticle reinforcement on mechanical properties and erosion–corrosion behavior of cast aluminum

AbstractThe effect of mixing alumina (Al2O3) nanoparticles in pure aluminum has been investigated, with a characterization of the mechanical properties and erosion–corrosion (E–C) behavior. Specimens of pure aluminum and Al with nanoparticles added as reinforcement have been produced by casting. Uniform dispersion of nanoparticles in the molten aluminum matrix has been achieved by mechanical stirring. Mechanical properties such as yield strength, ultimate strength, modulus of elasticity, and hardness of the new composites have been measured. E–C tests have been conducted to investigate the effect of the nanoparticle additives on the weight loss and surface properties of the new composites. Scanning electron microscopy, electron backscatter diffraction, and energy dispersive spectrometry have been employed to analyze, characterize, and compare pure aluminum and the composites. Al–Al2O3 nanocomposites have been obtained successfully and with a reasonable distribution by adding 1 wt.-% of alumina nanoparticles (100 nm or 20 nm in size) to molten aluminum. The alumina nanoparticles have increased the yield strength and hardness of the new composites when compared to pure aluminum. Enhancement in E–C resistance is also observed under various conditions.

Characterization of Hot Deformation Behavior of Nanosized Al₂O₃ Reinforced Al6061 Composites.

The hot deformation behavior of Al6061/Nano-Al₂O₃ composites were investigated at temperatures of 300 to 500 °C and strain rates of 0.001∼1/s using compression tests. The composite fabricated by the infiltration method consisted of an Al matrix and Al₂O₃ particles with a mean size of 200 nm. Interestingly, the true stress-true strain curves under all compressive conditions showed a peak stress at the initial stages of deformation, in which the peak stress increased with decreasing temperature and faster strain rate. The Z parameter, which is known as the temperature-compensated strain rate showed a linear relationship with the flow stress. The hot deformation mechanism is believed to occur through dynamic recrystallization, where fine equiaxed grains and dislocations were observed at the deformed specimens. A processing map was applied to evaluate the hot workability and flow instability region to determine the optimal deformation conditions of the composite.

On the in situ synthesis of (Fe,Cr)Al and (Fe,Cr)Al–Al2O3 nanostructured materials

In the present work, FeAl, (Fe,Cr)Al and (Fe,Cr)Al–Al2O3 intermetallic compounds were synthesized by mechanical alloying (MA), in which the intermetallic compounds were formed in one step at room temperature, and the nanocrystalline structure led to significant improvements of strength and ductility. Specifically, MA of a Fe50Al50 powder mixture led to the formation of the FeAl compound in 30 h with a grain size of about 80 nm. Increasing milling time to 100 h decreased the grain size to about 50 nm. In the next step, a Fe40Cr10Al50 power mixture was converted into a solid solution and then an intermetallic compound with a grain size of about 30 nm after 100 h of MA. Finally, the synthesis of nanocomposites with (Fe,Cr)Al intermetallic compound containing Al2O3 as the reinforcing phase was investigated. For this purpose, two different methods, the reduction of chromium oxide (Cr2O3) and hematite (Fe2O3), were examined. In the first method, a mixture of Fe–Al–Cr2O3 powder aluminum was milled and alumina phase was formed, but after 100 h of MA, the Cr2O3 phase was still observed. In the second method, a Cr–Al–Fe2O3 mixture was milled, and the heat of reaction immediately resulted in the formation of (Fe,Cr)Al nanoparticles with a grain size of about 29 nm, along with Al2O3 crystalline particles. The results of nanoindentation tests on these particles revealed that their hardness increases by chromium addition as well as Al2O3 reinforcing nanoparticles.

Investigation of strain-hardening characteristics of cold-sprayed Al–Al2O3 coatings: a combined nanoindentation and expanding cavity models approach

ABSTRACT The paper has taken a fundamental approach to study the nano-scale deformation behavior of Al-Al2O3 cermet coatings deposited by low-pressure cold spraying (LPCS) on AZ31 magnesium and Al6056 lightweight alloy substrates. Coating microstructural characteristics were first evaluated and correlated with LPCS process parameters using metallurgical characterization techniques: SEM, 3D optical profilometry, and XRD, followed by their microhardness and wear depth measurements and comparing with uncoated substrates under three-body abrasion wear. These properties were analyzed/mapped against probable deformation scenarios for nano-scale yield strength determination using the combined experimental nanoindentation load-depth curve method and computational expanding cavity models (ECMs). Obtained yield strength with key coating parameters like hardness and Young’s modulus were taken for modeling and simulation of strain-hardening effect under a peak loading of 165 mN in ABAQUS finite element (FE). Results from both combined experimental/computational and FE approaches indicate a progressive elasto-plastic mode being the dominating coating deformation mechanism with a strain hardening exponent of 0.15, under the studied loads.

Peculiarities of Granulation of the PAP-2 Aluminum Powder in the Technology of the Al–Al2O3 Powder Composite with a Layered Structure

An analysis of modern scientific-and-technical information evidences great prospects for using composite materials (CMs) based on the Al–Al2O3 system. It is shown in works of the Materials Science Department of the Moscow Aviation Institute that one promising method of fabricating aluminum-based CMs is the reaction sintering in air of blanks made of highly dispersed powders of the PAP-2 brand. However, to implement the proposed method in practice, it is necessary to solve a series of problems, in particular, associated with their low manufacturing properties, such as a lack of fluidity and extremely low apparent density. To granulate the PAP-2 aluminum powder, various process approaches are applied. They are based on process operations such as powder heating in air with subsequent isothermal holding at 350°C, introducing water-diluted sodium silicate glass into its composition, mechanical processing of the powder in a high-energy planetary mill, its heat treatment in vacuum at 650°C, and initiating the stearin saponification reaction on the surface of the PAP-2 flaked particles with the formation of the organic plasticizer component. It is found that the proposed granulation methods of the industrial PAP-2 powder make it possible to improve and vary the process characteristics of the initial powder, as well as modifying its composition and structure. The highest apparent density (up to 1.25 g/cm3) is attained when using the mechanical treatment of the initial powder in a high-energy planetary mill with the formation of rounded granules 50–150 μm in size. The most producible and cost-effective method is based on the initiation of the chemical reaction of stearin saponification on the surface of powder particles (the apparent density is ~0.4 g/cm3).

Design of the 3.0∼5.0 μm Band Wire-Grid Polarizer with Dielectric MgF2 and Metal Al Layers

Low refractive index magnesium fluoride (MgF2) dielectric layers with anti-reflection function were inserted between metal Al gratings and Al2O3 substrates in the form of continuous thin film and grating to construct type-I and type-II sub-wavelength wire-grid polarizers, respectively. The two types of wire-grid polarizers (type-1 and type-11) were designed to operate in the wavelength range of 3.0 similar to 5.0 Am. The structures of type-1 and type-II polarizers were optimized in terms of the substrate material, refractive index and thickness of dielectric layer using the finite-difference time-domain method. The results show that surface plasmon modes at the interface between Al gratings and Al2O3 substrate are weakened owing to the introduction of MgF2 dielectric layer, and a cavity mode in Al grating grooves begins to play a major role. In addition, equivalent refractive index of MgF2 dielectric grating is lower and MgF2 dielectric film is larger than the refractive index of ideal anti-reflection layer. Thus, MgF 2 dielectric grating has better antireflection function and higher transmittance towards the transverse magnetic polarization light. The distribution of electric field intensity indicates the existence of a cavity mode and stronger electric field intensity in the metal grating grooves of type-II. Higher TM transmittance and extinction ratio are achieved for type-11, which are obtained to be 99% and 30 dB at the wavelength of 4.0 mu m, respectively.

HITEMAL-an outer sheath material for MgB2 superconductor wires: The effect of annealing at 595–655 °C on the microstructure and properties

An aluminum material stabilized with a 1.6 vol% of nanometric Al2O3 dispersoids, named HITEMAL, was fabricated by hot extrusion of a fine atomized Al powder. The Al2O3 dispersoids stemmed from a native Al2O3 films on an aluminum powder surface. An extruded rod of the material was then cold-deformed out into a thin wire by rotatory swaging, hydro extrusion and rolling. Such severely deformed HITEMAL was studied as a prospective outer sheath stabilizer material for MgB2 core superconductor wires. An emphasis was put on the effect of annealing realized at various temperatures close to the melting point of Al, which is typically applied to form an in-situ MgB2 superconductive core, on the mechanical and electrical properties of the HITEMAL wire. A systematic investigation was performed of changes to a severely deformed Al grain structure and Al2O3 dispersoids upon annealing the as-deformed wire from 595 to 655 °C for 30 min. Mechanical and electrical properties of the wire were measured at room and cryogenic temperatures. The results showed that the ultrafine-grained Al + 1.6 vol% Al2O3 wire exhibited advantageous properties, and surface integrity after annealing up to 642 °C. It is thus a lightweight material of choice for outer sheaths of MgB2 superconductors.

Optimization of UV luminescence from ZnO thin film: A combined effect of Al concave arrays and Al2O3 coating

A synergistic effect of surface plasmons (SPs) and surface passivation on ZnO thin film optical performance was studied. The ZnO thin film of thickness of ca. 40 nm was deposited on Al concave arrays with a period (Dc) of about 125, 252, and 340 nm. Next, the Al2O3 coating thickness was tested with respect to UV light enhancement. About 20-fold enhancement of the UV emission was achieved upon simultaneous application of Al concave array with Dc ≈ 340 nm and 10 nm thick Al2O3 coating. Moreover, it was found that the Al concave array with Dc of ca. 125 nm does not sustain the SP resonance in UV region.

Lightweight MgB2 wires with a high temperature aluminum sheath made of variable purity Al powder and Al2O3 content

The properties of high temperature aluminum (HITEMAL, hereinafter HIT) composites made of powders with different particle sizes ranging from 0.8–3 μm and purities of 99.9%–99.996% were tested. The thermal, electrical, and mechanical properties of these materials were examined and compared with pure Al. Three different HIT materials were used for the outer sheath of single-core MgB2 wires with a Ti barrier manufactured by internal magnesium diffusion into a boron process. The critical currents, thermal stability, and strain tolerances of the MgB2/Ti/HIT wires were measured at liquid He temperature. It was found that the Al powder purity and particle size used for HIT affect the performance of MgB2 wires. A sheath made of high purity Al powder allows better thermal stability of MgB2 wire, but the strain tolerance is lower in comparison to the wire with HIT made of less pure powder and higher Al2O3 content. The presented wire configurations are promising for lightweight, thermally stabile, and strain tolerant superconducting MgB2 wires.

Improving compressibility and thermal properties of Al–Al2O3 nanocomposites using Mg particles

This work presents an efficient technique to improve compressibility and thermal properties of Al–Al2O3 nanocomposites. The compressibility behavior was examined by cold compaction test, and the thermal conductivity was calculated through the measured electrical resistivity of the prepared samples. The results showed that the addition of Al2O3 to Al matrix improves the compressibility behavior of the produced nanocomposite. However, it has a negative effect on the thermal conductivity of the produced composite. Adding Al2O3 hard particles accelerates the fracturing process which improves the compressibility behavior. However, it causes some agglomeration at the grain boundaries which reduce the thermal conductivity. The addition of Mg to Al–Al2O3 nanocomposite improves both the compressibility behavior and the thermal conductivity. This is due to the great reduction in the particle size and the agglomeration of reinforcement particles on the grain boundaries which improve the compressibility behavior and the thermal conductivity.

Electron backscattered diffraction analysis of friction stir processed nanocomposites produced via spark plasma sintering.

In the present study, Spark Plasma Sintered (SPSed) aluminium matrix composites were severely deformed through Friction stir processing (FSP). Pure aluminium powders and bimodal sized Al2 O3 particles (80 nm and 25 μm) were firstly mixed by ball milling and then consolidated by spark plasma sintering. The effect of the heat input as well the bimodal particle size of the alumina on the materials' microstructure and texture development was evaluated by electron back scattered diffraction (EBSD) analysis. The EBSD analysis clearly showed that the SPSed nanocomposites possessed bimodal aluminium matrix grain structure as well as a crystallography characterised by random texture. In addition, microstructural examination revealed that the partial recrystallisation occurred during SPS for all the nanocomposites. Also, it is revealed that the Zener pinning effect of Al2 O3 nanoparticles retarded recrystallised grain growth following recrystallisation during FSP and then leading to grain refinement of the aluminium. The results revealed that the heat generated during FSP has a remarkable effect on the grain distribution as well as on the crystallographic orientation. Also, a mixture of {112} <110> shear elements and an ideal strong B/B¯ component were observed. The microstructural changes, occurred during FSP in the stir zone region for Al-Al2 O3 nanocomposites, were attributed to both the discontinuous along with the continuous recrystallisation (DDRX/CDRX). It should be pointed out that with increasing the heat input, recrystallised grains portion increased.

Effect of metal coating of reinforcements on the microstructure and mechanical properties of Al-Al2O3 nanocomposites

ABSTRACTThe effects of various methods of reinforcement modification on the microstructure and mechanical properties of Al–Al2O3 nanocomposites were investigated. Alumina nanoparticles were modified by electroless deposition of Cu, Ni and Co. Subsequently, aluminium matrix nanocomposites reinforced with uncoated and coated nanoparticles were produced by the stir casting method. The results of microstructural analysis showed improved wettability of coated nanoparticles in the molten aluminium alloy. Furthermore, coated nanoparticles exhibited a more desirable interface with the matrix and were homogenously distributed within it. The mechanical properties of the nanocomposites were improving significantly when coated nanoparticles were used as reinforcements. Among the reinforcement modification methods, Ni-coating was recognised as being more effective for improving the mechanical properties of Al–Al2O3 nanocomposites.