Dispersion Of Al2O3 Particles Research Articles

Preparation of thermal interface materials with high thermal conductivity through the synergistic effect of Monoalkoxy-Terminated polysiloxane and branched siloxane oligomers

Four mono-alkoxysilyl-terminated asymmetric siloxane oligomers and a dimethylvinylsilyl-terminated branched-chain structure siloxane oligomer were prepared by a series of reactions to improve the filling loads and dispersion of Al2O3 particles in the polysiloxane matrix. Their influence on the surface modification of Al2O3 particles and the viscosity of composite materials was investigated. When the branched-chain siloxane oligomer was not used, mono-trimethoxysilyl-terminated asymmetric siloxane oligomers exhibited the best modification effect on the Al2O3 surface, and the silicone paste prepared by filling 70.8 vol% mixed-size Al2O3 particles had the lowest viscosity. When the branched-chain siloxane oligomer was used, the filling load of the modified Al2O3 particles could be further increased to 84.3 vol% under the synergistic effect of the mono-trimethoxysilyl-terminated asymmetric siloxane oligomers and the branched-chain siloxane oligomer. The viscosity of the silicone paste decreased with the increase in the polymerization degree of the dimethylsiloxane segment in the-mono trimethoxysilyl-terminated asymmetric siloxane oligomers. Meanwhile, the thermal conductivity of these silicone pastes also exhibited an increasing trend with the increase in the polymerization degree of the asymmetric siloxane oligomers. A thermal interface material with a thermal conductivity higher than 8.0 W/(m·K) was successfully prepared by using the asymmetric siloxane oligomers as the surface modification agent for Al2O3 particles and the branched-chain siloxane oligomer as the fluidity modifier for silicone paste.

Effect of P and Ti on the agglomeration behavior of Al2O3 inclusions in Fe–P–Ti alloys

Abstract Nozzle clogging occurs in the interstitial free (IF) steel with high phosphorus (P) more frequently than in IF steel with lower P. To explore the effect of P and Ti on the inclusion behavior in liquid steel, the in situ experiment and theoretical calculations were conducted. High-temperature confocal laser scanning microscopy was used in situ to observe the inclusion behavior at the liquid Fe–P–Ti alloy surfaces, and the attractive and capillary forces were also calculated to quantitatively estimate the effect of P and Ti on the inclusion behavior. The results show that the agglomeration of Al2O3 inclusions involves four steps: dispersed Al2O3 particles in liquid alloy; formation of Al2O3 chain structure; bending of the Al2O3 chain, and sintering and densification of the chain structure. The addition of Ti and P in the steel can increase the agglomeration time of inclusions, indicating the impeding effect of P and Ti on the inclusion aggregation. Furthermore, the orientation factor is proposed to estimate the direction of movement of the small inclusion crossing between large inclusions, and the experimental results confirm its validity.

Microstructural and electrochemical behavior of spark plasma sintered (Cu-10Zn) + Al2O3 nanocomposites

The present work deals with developing Al2O3 reinforced α-brass (Cu-10Zn) nanocomposites through spark plasma sintering and evaluated its electrochemical properties in a 3.5% NaCl aqueous solution. Microstructural analysis revealed the uniform dispersion of Al2O3 particles with inter-particle spacing ∼2.45 µm in 3 wt.% Al2O3 nanocomposites. The initiation of Al2O3 clustering and vast clustering of particles with wide particles-free-zone were observed in 6 and 9 wt.% Al2O3 nanocomposites. X-ray diffraction peaks confirm the crystallinity and incorporation of Al2O3 in the α-brass matrix. The corrosion behavior was studied by measuring the change in open-circuit potential values, electrochemical impedance spectroscopy (EIS), linear sweep voltammetry (LSV), and potentiodynamic polarization (PDP) studies in 3.5% NaCl solution. The 3 wt.% Al2O3 nanocomposites exhibited lower icorr value than the Cu-10Zn matrix and other Al2O3 reinforced nanocomposites. The EIS results confirm the surface layer enhancement and resistance to charge transfer in 3 wt.% Al2O3 nanocomposites due to their uniform distribution in the matrix. The uniformly embedded reinforcement particles abridged the prospects of galvanic coupling, which resulted in the upliftment of corrosion resistance and passivation behavior. An increase in the icorr value beyond 3 wt.% Al2O3 nanocomposites was due to the clustering of reinforced nanoparticles and vast particle-free zones and caused intergranular corrosion.

YÜKSEK ENERJİLİ ÖĞÜTME İLE ÜRETİLEN Al2O3 TAKVİYELİ CU KOMPOZİTLERDE PARÇACIK BOYUTUNUN ETKİSİ

Production of copper (Cu) composites with a reinforced Cu matrix using mechanical alloying with Aluminum oxide (Al2O3) particles of different sizes was achieved using high-energy ball milling procedure. The initial materials consisted of inert gas-atomized spherical electrolytic Cu powders containing 0.5 wt. % commercial Al2O3 powders, with particle sizes ranging from 10 µm to 1 µm. Cu powders with different particle sizes of Al2O3 were high-energy ball milled at 500 rpm for 3 hours to attain a consistent distribution of Al2O3 throughout in the Cu matrix. The powders that were high-energy ball milled were then subjected to cold-pressing at 500 MPa and isothermally sintered for 1.5 hours at 880°C in an Ar atmosphere. The fabricated copper composite materials were characterized using X-ray diffraction analysis (XRD), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDXS), density and macrohardness tests. The wear properties and mechanism were investigated through tribological pin-on-disc experiments, which revealed that the reinforcing effect was more significant when finely dispersed Al2O3 particles were combined into the Cu matrix compared to coarse Al2O3 particles.

Nanocrystalline Ag–Cu–Al Alloy thin films with densely dispersed alumina particles prepared using reactive sputtering method with Ar–O2 mixed gas

As a first step to challenge the fabrication of highly O2-permeable Ag membranes, thin films of nanocrystalline Ag–Cu–Al alloys with densely dispersed Al2O3 particles were successfully prepared via reactive sputtering using Ar–O2 mixed gas. The effect of O2 partial pressure on the thin film structure during sputtering was investigated. A critical O2 partial pressure was required to obtain a nanocrystalline structure via simultaneous internal oxidation during sputtering. The critical condition was correlated with the flux ratio of O2 to Al impinging on the Ag film surface and the stoichiometric ratio of O to Al in Al2O3.

Localised surface modification of high-strength aluminium–alumina metal matrix composite coatings using cold spraying and friction stir processing

ABSTRACT This study presents a novel approach for surface repairs of high-strength, cold-worked aluminium (Al) alloys, without negatively affecting the base material strength. Low-pressure cold spraying was used to fabricate Al–Al2O3 metal matrix composite overlays, with varying concentrations of Al2O3 deposited on an Al alloy. Friction stir processing (FSP) was employed to disperse and consolidate the overlay coating on the base material. The FSP was found to improve the Al2O3 particle distribution in the coating and reduce the mean free path between Al2O3 particles. The coating hardness increased after FSP. The post-FSPed overlays also exhibited lower wear rates compared to the as-sprayed condition. Remarkable improvement was observed in the tensile properties of the coatings, which were attributed to the improved dispersion of Al2O3 particles in the matrix, while the enhanced ductility was attributed to the possible grain refinement that occurred due to the recrystallisation of Al during FSP.

Effects of oxides nanoparticles on the microstructure and properties of Mo composites prepared via SPS sintering

Simultaneous achieving the second-phase particle strengthening, high density, and fine grain is a great difficulty for designing and preparing Mo alloys. In this study, the effects of γ-Al2O3 and Y2O3 nanoparticles on the microstructures and properties of Mo composites prepared via spark plasma sintering (SPS) were systematically investigated. It was found that for pure Mo and Mo–Y2O3 powders, Mo compact with both high density and fine grain size can't be achieved. However, Mo-Al2O3 composite with both a relatively high density (98%) and a fine grain size (1.67 μm) was synthesized successfully. The small γ-Al2O3 particles transformed into larger κ-Al2O3 particles by obvious grain boundary migration and grain growth in the sintering process, which effectively pinned the migration of Mo grain boundary with few effects on the surface atom diffusion of Mo. Moreover, there was a crystallographic orientation relationship between the κ-Al2O3 particles and Mo matrix (Mo (110)//Al2O3 (134‾1)). Ultrafine Mo composite containing dispersed Al2O3 particles with stable boundary adhesion can efficiently hinder dislocation movement and crack propagation, resulting in the obvious enhancements of bending strength, hardness and compressive yield strength.

Microstructure and Mechanical Properties of W-Al2O3 Alloy Plates Prepared by a Wet Chemical Method and Rolling Process.

The uneven distribution and large size of the second phase weakens the effect of dispersion strengthening in ODS-W alloys. In this article, the W-Al2O3 composite powders were fabricated using a wet chemical method, resulting in a finer powder and uniformly dispersed Al2O3 particles in the tungsten-based alloy. The particle size of the pure tungsten powder is 1.05 μm and the particle size of W-0.2 wt.%Al2O3 is 727 nm. Subsequently, the W-Al2O3 alloy plates were successfully obtained by induction sintering and rolling processes. Al2O3 effectively refined grain size from powder-making to sintering. The micro-hardness of the tungsten alloy plates reached 512 HV0.2, which is 43.7% higher than that of pure tungsten plates. The nano-hardness reached 14.2 GPa, which is 24.1% higher than that of the pure tungsten plate; the compressive strength reached 2224 MPa, which is 37.2% higher than that of the pure tungsten.

Non-uniform high-temperature oxidation behavior of twin wire and arc additive manufactured Ni3Al-based alloy

Ni3Al-based alloy fabricated by twin wire and arc additive manufacturing exhibited periodic remelting bands (RB) with unique microstructural characteristics. In this work, the deposited Ni3Al-based alloy was oxidized at 1100 °C for different times to investigate the high-temperature oxidation difference caused by RB. The differences in the microstructure, grain orientation, oxidation behavior, and oxidation mechanism between RB and non-RB were systematically studied. The results showed that these RB, epitaxially grown on the non-RB during each deposition layer, displayed similar Goss textures but a higher proportion of γ + γ′ dual-phase microstructure compared to non-RB. The oxidation of the deposited Ni3Al-based alloy obeyed parabolic growth kinetics at 1100 °C for 10 h and the oxidation scales were consisted of external NiO layer, intermediate NiAl2O4 layer with dispersed Al2O3 and TiO2 particles and internal Al2O3 layer. The outward diffusion of Al and Ti elements during the oxidation process led to the decomposition of γ′ precipitations and the formation of γ′-reduced layer beneath the Al2O3 layer. The cross-section microstructure of oxidation scales indicated that the RB displayed thicker scales and poorer oxidation resistance than non-RB. The oxidation rate of the deposited Ni3Al-based alloy was controlled by the outward transport rate of the total cations (Ni2+, Al3+, and Ti4+) through the Al2O3 layer. Initial oxidation and diffusion interface analysis demonstrated that the γ + γ′ dual-phase had a higher outward transport rate of the cations, which was responsible for the thicker oxide scales on the RB.

Morphological, mechanical, and thermal properties of polyurethane nanocomposites co‐incorporated with micro‐ Al 2 O 3 /nano‐ Al 2 O 3 for flexible thermal conductive component applications

Thermoplastic polyurethane (TPU) nanocomposites (TPU/μmAl2O3-ACA/nmAl2O3) with excellent mechanical, thermal stability and thermal conductivity were fabricated by co-incorporating aluminate coupling agent DL-411 chemically functionalized micron Al2O3 (μmAl2O3-ACA) and nano-Al2O3 (nmAl2O3) through melt blending method. FTIR analysis indicated that DL-411 has been successfully grafted on the surface of μmAl2O3, which was beneficial to the homogeneous dispersion of Al2O3 particles and enhancements of interfacial interactions between Al2O3 particles and TPU matrix. Adding μmAl2O3-ACA and nmAl2O3 simultaneously showed obvious synergistic effects on improving the mechanical properties of TPU nanocomposites. The optimum mechanical properties were obtained at the mass ratio of μmAl2O3-ACA to nmAl2O3 of 3:1. Both μmAl2O3-ACA and nmAl2O3 particles were homogeneously dispersed, constructing relatively perfect thermal conductivity networks, as verified by FESEM and PLM observations. The thermal conductivity (k) of TPU nanocomposites increased continuously with the addition of μmAl2O3-ACA/nmAl2O3 particles, and the optimal k (0.28 W/m K) was achieved when the mass ratio of μmAl2O3-ACA to nmAl2O3 was 3:1, which increased by 53% compared with pure TPU (k = 0.183 W/m K). TGA showed that, in contrast to those of pure TPU, the maximum decomposition temperature of TPU/μmAl2O3-ACA/nmAl2O3 nanocomposites increased by 77.77°C, and the decomposition activation energy of TPU nanocomposite enhanced by 178%.

High anti-arc erosion performance of the Al2O3 reinforced Cu@W composites for high voltage circuit-breaker contacts

High voltage circuit-breakers with superior performance are demanded as the transmission distance extends and voltage rises, which are often subject to high current and voltage surges. Commercial circuit-breaker contacts are conventionally manufactured with CuW alloy by infiltration method, limiting their performance improvement in withstanding current (or voltage) and lifespan. In this paper, we optimize the microstructure and component of Al2O3 reinforced Cu@W80 composites (Al2O3/Cu@W80), which fabricates the Cu@W powder first by chemical coating and the composites by spark plasma sintering (SPS) method. The composites exhibit enhanced hardness (maximum value up to 273 HV) due to the addition of Al2O3 powder and a more homogeneous and refined tungsten phase compared to the CuW counterpart. Moreover, the dispersed Al2O3 particles with low work function become the preferred ablation phase and guide the electrical arcs, further improving the anti-arc erosion performance of Al2O3/Cu@W80. Our findings suggest that the Al2O3/Cu@W80 composite with optimized components could be potentially used as a candidate for high-voltage circuit-breaker contacts.

Preparation and properties of Al2O3 dispersed fine-grained W-Cu alloy

In this study, high-performance fine-grained W-Cu sintered blocks with the addition of dispersed Al2O3 particles were successfully produced by low temperature liquid-phase sintering, using the raw material of ultrafine W-Cu alloy powder. The ultrafine W-Cu alloy powder was obtained by a two-step reduction process composed of stages of carbothermal reaction and hydrogen deep deoxidation. The fine Al2O3 grains with uniform distribution in W-Cu alloy were introduced by spray method, leading to the decrease of W grain size and W-W connectivity. The relative densities of all sintered blocks were>97%, and a higher degree of densification ensures that the alloy has excellent comprehensive properties. With the increase of Al2O3 content, W grain size and W-W connectivity of sintered W-Cu samples decrease from 664 nm to 472 nm and 0.2 to 0.14, respectively. The W-Cu alloy with the ultimate tensile strength of 415 MPa and the highest elongation of 7.22% was obtained when the addition amount of Al2O3 was 0.5 wt%. At the same time, it also possessed the maximum bending strength of 1028 MPa and microhardness of 312 HV, respectively. In addition, due to the good network structure of Cu and uniform three-phase distribution, the sintered samples had excellent conductivity and compressive strength.

Strengthening mechanism and effect of Al2O3 particle on high-temperature tensile properties and microstructure evolution of W–Al2O3 alloys

The W–Al2O3 alloy rods were successfully fabricated by the powder metallurgy process and hot swaging. Subsequently, the high-temperature tensile tests were conducted to characterize the mechanical properties of the W–Al2O3 alloy. At 800 °C, the ultimate tensile strength of W-0.25 wt% Al2O3 alloy is 611.1 MPa, which is 18% higher than that of pure W. After tension, the microstructure evolution was evaluated using metallographic microscope and transmission electron microscopy. For the pure W undergoing deformation at 1000 °C, dynamic recrystallization occurs, leading to the sharp decrease of the strength. However, the microstructure of the W-0.25 wt% Al2O3 alloy contains a large number of sub-grain and low-angle grain boundaries, which does not significantly change in the temperature range of 800–1200 oC, and the work hardening plays a leading role during the high-temperature deformation process. Due to high hardness, the dispersed Al2O3 particles effectively prevent the dislocation movement, displaying a significant strengthening effect.

Studies and Research on the Influence of Deposit Parameters on the Characteristics of Composite Coatings Ni-Al2O3 Obtained by Electrochemical Methods

The paper presents the characterization of composite coatings with nickel matrix using as dispersed phases Al2O3 particles, both from the microstructural point of view and from the point of view of the layer thickness, micro-hardness and corrosion behavior in saline fog. The presence of dispersed phase particles led to the finishing of the structure because they acted as nucleus centres, reducing the size of nickel crystallites. The parameters of the deposits influence the structure and properties of the obtained layers.

Flexible transparent projection screen of polycarbonate matrix integrated with functionalized alumina particles

AbstractSolution blending approach was introduced to prepare flexible Polycarbonate (PC)‐based composited films with excellent transparent projection performance. After modified by an aluminate coupling agent DL‐411(ACA‐1), alumina (Al2O3) possesses improved dispersity. There may form oxygen bridge between aluminum atoms on Al2O3and ACA‐1. With the long aliphatic chain directing outwards, the compatibility between PC and modified Al2O3was significantly improved. The dispersion of Al2O3particles in PC was therewith promoted. After vacuum drying, well‐blended mixtures were developed and PC films containing Al2O3clusters can be prepared. The composite films have good light transmission and diffuse reflection effects. When Al2O3/PC mass ratio is beneath 0.2, the composited films possess excellent transparency comparable with pure PC film. The diffuse reflection performance of PC composite films is gradually enhanced with the increase of Al2O3content. When Al2O3/PC ratio attains 0.1, the visible light reflectance amounts 15%, which can even exceed 30% with the ratio reaches 0.5. The composite films show improved resistance to UV irradiation as the visible light reflectance and transparency are comparable to un‐radiated samples. The hydrophobicity of composite films with a certain Al2O3amount increases, which brings forth good anti‐moisture property for these transparent projection screen films.

Effect of Friction Stir Processing Parameters on the Properties of AA7075-T73/Al2O3 Surface Metal Matrix Composite

Friction Stir Processing (FSP) technology was wielded to output the Al7075/ Al2O3 surface composite. The effects parameters of processing method on particle distribution have been studied. The microstructure and mechanical characteristics of the samples were examined using the optical microscope, SEM and hardness examination. Acquired consequences, showed that Al2O3 particles were in a good interior distribution inside the basement. This technique produced excellent bonding between the surface composite and the base material. On other hand the surface hardness was increased about 25% as compared with the substrate. In addition, grain matrix refinement and enhanced particle distribution were obtained after each FSP pass. Also the dispersion of Al2O3 particles in the stirred area became more homogeneous and the average hardness improved by increasing the number of passes.

Experimental study on corrosion-erosion behavior of ITER blanket structure materials in flowing Pb-17Li

Abstract A rotating corrosion test device has been developed to study the compatibility between liquid tritium breeder material and structure materials for fusion facility. The corrosion behaviors of three samples made of reduced activation ferritic/martensitic steel (RAFMS), 316 L stainless steel and oxide dispersion strengthened steel (ODS), are studied in liquid Pb-17Li at 500℃ for an exposure of 1000 h. The weight changes of the specimens are obtained before and after test. The analyses of surface morphology and component are characterized by SEM, EDS and XRD methods. Results show that weight-loss rate of RAFMS is lower than that of 316 L and ODS in the experiment. It indicates that the corrosion mechanism is governed by some or all dissolution of alloy elements (such as Cr, Ni) from the sample surface into liquid Pb-17Li and the exfoliation from the corroded surface by the flowing Pb-17Li. Specifically, the dispersed Al2O3 particles in ODS is easy to be corroded in liquid Pb-17Li and then provide corrosion points to accelerate dissolution of Ni-Fe austenite. The compatibility of RAFMS with liquid Pb-17Li is slightly better than that of 316 L and ODS in the current experimental period.

Effect of Electrically Assisted Accumulative Roll Bonding (EARB) Process on the Mechanical Properties and Microstructure Evolution of AA5083/Al2O3 Composites

Abstract In this study, electrically assisted accumulative roll bonding (EARB) process has been proposed and applied to produce metal matrix composite (MMC: AA5083/-1 % aluminum oxide [Al2O3]). This process can be used to fabricate the MMCs needed in various industries such as automobile and aerospace with appropriate mechanical properties. The alloy was deformed in various electricity current levels, i.e., at 0, 100, 200, and 300 A up to six ARB cycles (ε = 4.8). The mechanical properties of the deformed material have been measured by a tensile test, Vickers microhardness test, and scanning electron microscopy. Microstructure evolution during the EARB cycles leads to improvement of the strength and elongation amount of samples. According to the results obtained, uniform dispersion of Al2O3 particles improves both the strength and tensile toughness of the composites. Also, it was established that the electricity current had a significant effect on the mechanical and microstructure properties of the manufactured MMCs. High strength, low elongation, and high average Vickers microhardness were obtained for the material processed at lower current intensities. Whereas, by increasing the electricity current intensity up to 300 A, the tensile toughness and elongation amplitudes improved considerably.

Al2O3 Coatings on Zinc for Anti-Corrosion in Alkaline Solution by Electrospinning

The severe corrosion accompanied with hydrogen evolution reaction has become the main obstacle restricting the utilization of zinc as an electrode in alkaline batteries. Al2O3 coating helps control the corrosion of zinc in alkaline solution. Herein, a stable Al2O3 coating is fabricated through facile electrospinning from Al(NO3)3 as an efficient anti-corrosion film on zinc. The electrospinning technique facilitates uniform dispersion of Al2O3 particles, therefore the corrosion inhibition efficiency could be up to 88.5% in this work. The Al2O3 coating prevents direct contact between zinc and the alkaline solution and minimize hydrogen evolution. Further, the effects of the thickness of Al2O3 coating on corrosion behavior of zinc are investigated through hydrogen evolution reaction, Tafel polarization, and impedance test. The results show that the thicker Al2O3 coating possessed better corrosion inhibition efficiency due to the higher corrosion resistance and lower porosity. The 18 μm Al2O3 coating on zinc provides corrosion current density of 60.6 mA/cm2, while the bare zinc substrate delivers as much as 526.3 mA/cm2.This study presents a promising approach for fabricating Al2O3 coating for corrosion-resistant applications.

Development of Accident-Tolerant FeCrAl Steels Containing Al2O3 Particles by Means of Internal Al Oxidation

FeCrAl ferritic steels containing dispersed Al2O3 particles instead of Y2O3 or Ce2O3 particles were developed for accident-tolerant fuel cladding in light-water reactors. Forcible addition of only oxygen through mechanical alloying can create Al2O3 particles by precipitation during annealing above 973 K. The oxygen content was controlled to use oxidation of internal aluminum to form Al2O3 particles and increase the number density of Al2O3 particles with an average diameter of around 40 nm. The size and number density of Al2O3 particles are significantly affected by lattice misfit, and thus interfacial energy between Al2O3 particles and the matrix, and by aluminum solubility into the ferrite matrix. The estimated Al2O3 particle strengthening stress is consistent with measured tensile stress at 973 K. Both stresses are slightly improved with increasing oxygen content, but are half the level of that in steel strengthened by Ce2O3 and CeAlO3 particles.