Al2O3 Particles Research Articles

Investigations on microstructure, hardness and tribological behaviour of AA7075-Al2O3 composites synthesized via stir casting route

Aluminium matrix composite (AMC) materials play an important role in the field of automobile and aerospace industries due to their excellent properties. In this research, aluminium alloy (AA7075) was reinforced with alumina (Al2O3) particles to improve their hardness and tribological behaviour of the base alloy. Four composites were prepared by varying the content (4, 8 and 12 wt.%) of Al2O3 particles through the stir casting technique. The surface morphology of the proposed composites ensured the uniform distribution of Al2O3 particles into the matrix alloy. The hardness of the composite was measured using a Brinell hardness tester and the maximum value of hardness was found in the AA7075 - 8 wt.% Al2O3 composite. Hence, a tribological investigation was carried out on this AA7075 - 8 wt.% Al2O3 composite. Load (P), sliding speed (V) and sliding velocity (D) were taken as the wear parameters for conducting the experiments. A Technique for Order Preference by Similarity to Ideal Preferred Solution (TOPSIS) approach has been applied to find out the optimal conditions of parameters to obtain the lowest wear rate (WR) and the co-efficient of friction (COF). The results showed that the lowest WR and COF was obtained at ‘P’ of 15 N, ‘V’ of 1 m•s-1 and ‘D’ of 1000 m•s-1. ANOVA results revealed that ‘P’ is the factor with the most significant contribution (38.36%), followed by ‘D’ (28.32%). The worn surface morphology of the confirmation experiment specimen was investigated by SEM and the wear mechanism was reported.

Thermal Conductivity and Orientation Structure of Liquid Crystalline Epoxy Thermosets Prepared by Latent Curing Catalyst

Improvements in the performance of electronic devices necessitate the development of polymer materials with heat dissipation properties. Liquid crystalline (LC) epoxies have attracted attention because of the orientation of their polymer network chains and their resultant high thermal conductivity. In this study, a diglycidyl ether of 1-methyl-3-(4-phenylcyclohex-1-enyl)benzene was successfully synthesized as an LC epoxy and the LC temperature range was evaluated via differential scanning calorimeter (DSC). The synthesized LC epoxy was cured with m-phenylenediamine (m-PDA) as an amine-type curing agent and 1-(2-cyanoethyl)-2-undecylimidazole (CEUI) as a latent curing catalyst, respectively. The LC phase structure and domain size of the resultant epoxy thermosets were analyzed through X-ray diffraction (XRD) and polarized optical microscopy (POM). High thermal conductivity was observed in the m-PDA system (0.31 W/(m·K)) compared to the CEUI system (0.27 W/(m·K)). On the other hand, in composites loaded with 55 vol% Al2O3 particles as a thermal conductive filler, the CEUI composites showed a higher thermal conductivity value of 2.47 W/(m·K) than the m-PDA composites (1.70 W/(m·K)). This difference was attributed to the LC orientation of the epoxy matrix, induced by the hydroxyl groups on the alumina surface and the latent curing reaction.

Microstructure evolution and mechanical property of W-Ni3Al alloy by adding minor Co element

In this study, W-Ni3Al alloys with fine grain size and outstanding integrated mechanical properties were fabricated based on mechanical alloying and spark plasma sintering (SPS), modified by adding a small amount of cobalt powder. It was found that the alloy was strengthened by the diffusion of Co and W elements into the Ni3Al lattice to form (Ni,Co)3(Al,W) solid solution during the sintering, where Al2O3 particles in-situ formed at the interface between binder phase and tungsten grains, and therefore became obstacles to impeding the dislocation movement. Such obstacles would lead to restraints of dissolution-reprecipitation of tungsten grains, resulting in refined tungsten grains and strengthening effect in the sintered alloys. The synergistic effect of these two kinds of strengthening significantly improved the mechanical properties of W-Ni3Al alloy. As a result, the W-9Ni3Al-1Co alloy sintered at a low temperature of 1250 °C had the best room-temperature mechanical properties, and its bending strength, tensile strength and hardness were 1519.48 MPa, 783.24 MPa and 71.1 HRA, respectively.

Assessing dispersion stability of alumina colloids via thermal characterization of the sediment layer

Colloidal suspensions incorporating particles are pivotal in diverse industries because of their distinct properties. However, challenges such as particle aggregation and sedimentation have impeded their widespread application. Existing techniques for assessing dispersion stability have limitations with respect to the particle type, concentration, and suspension properties. This study focuses on an innovative approach for assessing the dispersion stability and presents a streamlined method for analyzing the particle size and distribution. A theoretical model considering gravity, buoyancy, and viscous forces acting on the particles was developed to calculate the time-varying thickness of the sediment layer at the bottom of the sample colloid. The 3ω method is employed to measure thermal resistance changes at the sample droplet's bottom due to sedimentation. An empirical comparison utilizing Al2O3 particles in deionized water validates the efficacy of the method in understanding sedimentation mechanisms. In addition, a stability constant was proposed to quantitatively compare sedimentation phenomena, factoring in mixing methods, time, particle concentration, and shelf time. This study enhanced the quantification of the dispersion stability of colloids by enabling swift and precise assessment of particle concentration, size, and distribution inside a sample droplet.

Influence of ageing temperature on the tribological characteristics of LM25/Al2O3/SiC hybrid metal matrix composite for lightweight applications

The demand for hybrid composites has lately increased due to their extraordinary qualities, which include unique mechanical, tribological, and physical capabilities not found in other materials. These composites improve performance and utility by mixing different reinforcing components, making them highly sought after. However, there is a study gap on the effects of long-term ageing on the tribological characteristics of LM25 (Al–6.6Si–0.2Mg)/Al2O3/SiC metal matrix composites (MMCs). As a result, extensive studies on the influence of ageing temperature on the tribological properties of LM25/Al2O3/SiC MMCs via long-term ageing effects still need to be included. Therefore, this study investigated the metallurgical and hardness properties of stir-cast LM25 alloy reinforced with Al2O3 and SiC particulates with varying ageing temperatures. Furthermore, dry sliding wear behaviour is also examined. The investigation concluded that adding micron-sized Al2O3 and SiC particles to LM25 improves hardness and tribological properties. As the ageing temperature increased, the eutectic particles became coarser. Furthermore, the result illustrates that the coefficient of friction (COF) values also enhanced with wear rates. Higher loads increased the wear rate and COF, whereas higher sliding speeds decreased the COF and wear rate.

Studies on thermal stability, softening behavior and mechanism of an ADS copper alloy at elevated temperatures

An Al2O3 dispersion strengthened (ADS) alloy with an ultra-high softening temperature of ∼1200 K was fabricated by the in-situ internal oxidation and reduction methods. The evolution of the nanometer Al2O3 particles, grain size, and consequently the softening behavior of this ADS alloy, were investigated by conducting the annealing treatments in the range from 673 K to 1273 K for 60 min. These refined nanometer Al2O3 particles were found to be highly stable at elevated temperatures, leading to the high dislocation density and grain boundary stability of the matrix. The average grain size was found to increase extremely slowly from ∼0.60 μm to ∼0.74 μm with increasing annealing temperatures from 773 K to 1273 K. A criterion for grain boundaries migration and softening was established based on the competition between grain growth and pinning effect of Al2O3 particles. The strong pinning effect of Al2O3 particles was found when the grain size was between the lower limit (about 0.4–0.5 μm) and upper limit (2.18 μm). The occurrence of softening behavior was attributed to the rapid increase of the proportion of grains larger than the upper limit. A modified Hall–Petch relationship was established by introducing the integration of the grain size distribution, which can describe this correlation between softening behavior and the pinning effect of Al2O3 particles. The current study not only sheds light on the further understanding of the softening mechanism of ADS copper alloy but also provides a useful route for designing copper alloy with high softening resistance.

Mechanism of self-reaction evolution of Fe@ Al2O3 catalyst for growing carbon nanotube array

In this work, for the synthesis of CNT arrays, a one-step heat-treated aluminum foil substrate-supported Fe(NO3)3 solution “self-reactive process” was developed to prepare Fe@Al2O3 nanoparticles with a diameter of about 20 nm and a catalyst layer thickness of about 2–3 mm. The results show that the key to maintain the small nanoparticle state is the interfacial interaction between the metal and the metal oxide, which enables the Fe nanoparticles to anchor on the Al2O3 surface and effectively prevents the aggregation or segregation of the Fe nanoparticles. Furthermore, by comparing the characterization parameters of the catalyst nanoparticles prepared under a series of different conditions, it was found that the aluminum foil substrate was oxidized to Al2O3 by the Fe(NO3)3 precursor in a one-step heat treatment, which could be explained by the oxidation of nitrate ions. Meanwhile, the core-shell structure formed by some of the Al2O3 particles with the catalyst prevented the agglomeration of the catalyst during the reduction process by co-deposition of metal oxides with Fe catalyst. This method saves a lot of time compared with other catalyst preparation methods for growing CNT.

NANOPARTİKÜL İLAVESİNİN BENZİNİN KIRILMA İNDİSİ VE YOĞUNLUĞU ÜZERİNDEKİ ETKİSİNİN ARAŞTIRILMASI

In this study, the use of Al2O3 and TiO2 nano particles with a size of 12 nm and a purity of 99.9% as gasoline fuel additives was investigated. Fuel mixtures were prepared using a 3-level factorial design technique, and density and refractive index values were determined. Al2O3 nano particles, due to their high surface area, increased the density by 0.17% (3.5 ppm) and 1.22% (7 ppm), while TiO2 nano particles increased the density by 0.22% (3.5 ppm) and 1.26% (7 ppm). It was observed that the nano particle with a higher surface area had a less significant effect on density. The refractive index values decreased by 0.11% (3.5 ppm) and 0.14% (7 ppm) for Al2O3 nano particles, and by 0.21% (3.5 ppm) and 0.24% (7 ppm) for TiO2 nano particles. This study highlighted the importance of particle size, purity, and surface area in the selection of nano particles. Based on the evaluations and preliminary tests, nano particle levels above 15 ppm exhibited a tendency for agglomeration in the fuel. It is crucial to limit the total concentration to 15 ppm, especially for nano particles with a high surface area like Al2O3, to achieve homogeneous fuel.

Effect of exposure temperature on the corrosion behavior of a FeNiCrCuAl high entropy alloy in supercritical water

The corrosion behavior of a FeNiCrCuAl high entropy alloy exposed to supercritical water at 380–650 °C and 25 MPa was investigated. The weight gain exhibited a nearly parabolic kinetics. At 380 °C, Al2O3 precipitated on Fe3O4 particles in FeCr-rich regions and intensified as the temperature increased to 650 °C, eventually resulting in an Al2O3 particle. A mixed Fe3O4 and NiAl2O4 outer layer developed on NiAl-rich regions at 380 °C, whereas an Al2O3 layer formed at 650 °C. Cu2O formed along the boundaries of NiAl-rich regions, regardless of exposure temperatures. The corrosion mechanism at different temperatures was elucidated.

The dominant factor of C/SiC composites in ablation environment with heat and particle flow

As thermal structure components in scramjet engines, carbon-reinforced silicon carbide (C/SiC) composites are often subject to an ablation coupled with heat and particle flows. This study simulates the working environment of the scramjet engine's thermal structure component by coupling an Al2O3 particle flow with a plasma flow. The ablation behaviour of C/SiC composites in the presence and absence of particle impact have been comprehensively analysed. The results show that the factor dominating the ablation behaviour varies with temperature. At relatively low temperatures, the particles have difficulty breaking down the dense SiO2 layer formed from the oxidation of SiC in the presence of heat flow which is the dominant factor. As the temperature rises, the SiC begins to shift towards active oxidation. A few defects appear in the oxide layer, leading to a significant particle mechanical flaking effect. Particle flow is the dominant factor. However, a higher temperature led to the substantial active oxidation of SiC, and the oxide layer dissipated, exposing more defects. The heat flow causes a strong oxidation reaction, and the scouring effect of the particles is significant as well, both of which play a dominant role in the ablation process.

Pengaruh Penambahan Filler Al2O3 dan TiO2 pada Resin Polyester terhadap Sifat Fisik dan Mekanik

Polyester composites have been developed to have high strength and light density, but the fracture occurs due to very little plastic deformation or low strain values, pre-failure detection is difficult in these composites due to the rapid propagation of cracks in the composite system. To increase the strength and delay failure, the addition of filler in the form of Al2O3 and TiO2 particles is carried out. The use of particles as fillers in polymer composite materials is increasingly being developed. In this study, Al2O3 and TiO2 particles (0%, 2%, 4%, 6%, 8%, 10% vol.) were added in polyester matrix BQIN EX 157. by casting method; the liquid homogeneous mixture was carefully poured into a simple mould to be air dried. The composites were cut to serve as specimens for density test, mechanical tests such as tensile and compressive tests. The results showed a density of 1.23 g/cm3, a maximum strength of 47 MPa for 2% additional Al2O3 filler, (tensile, decreasing ̴11%) and 120 MPa (compressive) for a maximum of 2% additional Al2O3 (compressive, decreasing ̴3%) with TiO2 filler. The decrease in strength was caused by uneven particle dispersion, voids and agglomeration that occurred during the casting process.

Mechanical properties and corrosion behavior of titanium surface biocomposites reinforced with Al2O3 particles fabricated by friction stir processing

This study aims to investigate the effects of Al2O3 micro and nanoparticles on the microstructure, mechanical, and corrosion properties of the pure titanium surface biocomposites fabricated by friction stir processing (FSP). The microstructure, mechanical, and corrosion properties of samples were evaluated using optical microscopy (OM), electron-backscattered diffraction system (EBSD), hardness tests, tensile tests, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) analyses. The OM and EBSD analyses proved the highest amount of grain refinement associated with the formation of strain-free recrystallized grains by applying FSP at the presence of Al2O3 nanoparticles. However, the amount of micro-strain and grain size of FSPed titanium without particles and with Al2O3 microparticles were much higher than that of samples with Al2O3 nanoparticles. Notably, the hardness values improved by about 33 % and 52 % by introducing Al2O3 microparticles and nanoparticles, respectively. Mechanical tests demonstrated a noticeable enhancement in the tensile strength of the samples, from 200 MPa for the sample processed without Particles to the highest amount of 294 MPa for that processed in presence of nanoparticles. The corrosion test results revealed a significant improvement in the corrosion resistance of the titanium samples by adding Al2O3 nanoparticles in which the corrosion potential increased from 0.244 to 0.192 V and charge transfer resistance from 394 to 794 kΩ cm2.

Interaction of water mists with bibulous filter media and hygroscopic particles in pressure drop jump of fibrous filter media

This study aims to quantitatively evaluate the impact of humid airflows (unsaturated and saturated airflows with water mists), water absorption by filters (wood cellulose and polyester fibre filter media) and hygroscopic loading dust (KCl and Al2O3 particles) on the pressure drop jump. Additionally, proposed methods to alleviate this tendency are known as the “wet blockage” of filters in practice. The experimental results demonstrated that the water content of the airflows mainly contributed to the pressure drop jump in the filters. Increasing the water content from 4.2 g/m3 to 11.3 g/m3 resulted in a fourfold decrease in the water-loading capacity of the tested filter medium. However, increasing the water absorption of the filters by a factor of three times caused a reduction in the water-loading capacity of approximately 42 mg/cm2 based on the self-defined parameter tc. Furthermore, the non-hygroscopic particles delayed the pressure drop jump, which is associated with the dust-holding capacity of filters.

Computational damage analysis of metal matrix composites to identify optimum particle characteristics in indentation process

This paper presents an integrated numerical model that investigates the effects of Al2O3 particle volume fraction, distribution, size, shape, and clustering on the deformation, damage, and failure behaviors of particle-reinforced metal matrix composites. Additionally, the effects of the cohesive strength of the matrix-particle interface and the initial void volume fraction on these behaviors are investigated. In this study, random microstructure-based finite element modeling approach is used. The Gurson-Tvergaard-Needleman model is used to capture the plastic deformation and ductile cracking of the matrix, whereas the Johnson–Holmquist II model is used to model particle fracture. The matrix-particle interface decohesion is modeled using the surface-based cohesive zone method. A two-dimensional nonlinear finite element model augmented with Python-generated code is developed in ABAQUS/Explicit to analyze the damage mechanisms in AA6061-T6/Al2O3 particle-reinforced metal matrix composites. The results show that Al2O3 particle enhance the ability of particle-reinforced metal matrix composites to resist deformation. However, this enhancement is dependent on the indentation location, particulate characteristics, and the applied load. An increase in the particle volume fraction increases the risk of particle fracture, particularly when particles are close to the material surface. Circular particles are the optimal choice for the reinforcement of particle-reinforced metal matrix composites. The predictions are in good agreement with the experimental data, particularly in terms of Rockwell hardness and deformation characteristics.

Influence of gradation in the reinforcement particles on the interfacial microstructure and mechanical properties of functionally graded composites

In this research, Al6061 alloy-based Functionally Graded Composites (FGCs) were fabricated by hot pressing which is composed of 7 layers with different proportions of Al2O3 reinforcement particles. The addition of Al2O3 particles is gradually increasing in the other layers from top to bottom (Layer 1 - Pure Al6061 alloy, Layer 2–5 wt% Al2O3, Layer 3–10 wt% Al2O3, Layer 4–20 wt% Al2O3, Layer 5–30 wt% Al2O3, Layer 6–40 wt% Al2O3, Layer 7–50 wt% Al2O3). Moreover, three different Al2O3 particle sizes (8, 16 and 32 µm) were used to fabricate three sets of FGCs. Reciprocating wear studies were performed and the result shows that the FGC with 8 µm Al2O3 particle size shows 85.5% improved wear resistance. Further, various wear mechanisms were investigated and finally compressive strength analysis proved that the homogenous distribution of Al2O3 particles in the FGC with 16 µm Al2O3 particle size helps achieve the maximum compression stress of 476.04 MPa compared with other FGCs.

Microwave plasma-produced Al/Al2O3 microparticles as precursors for high-temperature high-strength composites

Microwave plasma-produced Al/Al2O3 microparticles as precursors for high-temperature high-strength composites

Investigation of the interface state characteristics of the Al/Al2O3/Ge/p-Si heterostructure over a wide frequency range by capacitance and conductance measurements

In this work, Al/Al2O3/Ge/p-Si heterostructures were fabricated by e-beam thermal evaporation. The EDX (energy dispersive X-ray spectroscopy) map visually obtained the basic distribution information in a two-dimensional graph. Three-dimensional atomic Force Microscope (AFM) analysis of the roughness of the Al/Al2O3/Ge/p-Si heterostructure shows that the Al2O3 particle has approximately 4.35 nm. Quantitative analysis via histogram plots for Al2O3 interlayer grown on p-Si shows a Gaussian-like distribution, and it has a sharp profile between 0 and 2 nm on silicon, located around 1.2 nm. The current-voltage (I–V) and capacitance-conductance-voltage (C-G/ω-V) measurements were used to investigate the electrical properties of the structure at room temperature. The I–V measurements revealed two distinct linear regions, attributed to barrier inhomogeneity and distribution of interfacial state/trap densities (Dit). For this reason, we obtained Dit distributions by considering the voltage dependence of the ideality factor n(V) in two regions. Diode parameters acquired through different methods are comparatively presented with a brief literature review. Then, the C-G/ω-V measurements were conducted across a broad frequency range (from 0.3 kHz to 3 MHz), and these measurements revealed notable alterations in the electrical parameters with regard to frequency. In order to probe interface states/traps, we employed the conductance/admittance method, which provided satisfactory information about trap lifetime, following the low-high frequency (LF-HF) and Hill-Coleman methods. The effects of these states/traps on the measurements according to voltage, frequency, and energy level (Eit-Ev) are discussed in detail.

Effect of cold spray processing parameters on the microstructure, wear, and corrosion behavior of Cu and Cu–Al2O3 coatings deposited on AZ31 alloy substrate

Cold spray coatings represent a newly emerging and recently implemented approach to enhance the poor wear and corrosion resistance of AZ31 magnesium alloy. In this study, the authors applied pure Cu and Cu-50 wt% Al2O3 composite coatings on an AZ31B substrate using the cold spray deposition method and investigated the effects of gas pressure (1, 2, and 3 MPa) and stand-off distance (1, 2, and 3 cm) on their microstructure characteristics. An increase in gas pressure from 1 MPa to 3 MPa resulted in a decrease in porosity, ranging from 33 % to 38 %, across varying stand-off distances. Increasing the stand-off distance from 1 to 3 cm resulted in a nearly four-fold rise in porosity for 2 and 3 MPa pressures and about 1.5 times for 1 MPa. The porosity increased with higher pressure due to the fragmentation of Al2O3 particles but decreased with greater spraying distance due to reduced Al2O3 retention. Additionally, the incorporation of Al2O3 particles into Cu coatings led to a significant improvement in sliding wear resistance, by up to 50 %, compared to the bare substrate. Abrasive wear and delamination were identified as the dominant wear mechanisms for the composite coatings based on friction coefficient values and micromorphology of wear tracks. Electrochemical results indicated a significant increase in the corrosion resistance of the Cu coating compared to both the bare Mg substrate and Cu–Al2O3 coating, attributed to improved resistance to galvanic corrosion.

High-strength, high-porosity and low-shrinkage Al2O3 ceramics prepared by flexible adjustment of CaCO3 size and content

A high-strength, high-porosity and low-shrinkage Al2O3 ceramics was prepared by direct ink writing method (DIW) using CaCO3 as a mineralizer. The effect of CaCO3 size and content on the phase formation, microstructural evolution and properties of porous Al2O3 ceramics sintered at 1400 ℃ were systematically investigated. The results showed that the properties of the porous Al2O3 ceramics were significantly affected by the particle size and content of CaCO3. The fine particle size and increased CaCO3 content could enhance the effective contact area between CaCO3 and Al2O3, facilitating the reaction at high temperatures during the sintering at 1400 ℃. It was found that the favorite sintering condition promoted the formation of calcium hexaluminate (CA6) and calcium dialuminate (CA2). Microstructure analysis revealed that CA6 exhibited a lamellar and tabular morphology, concentrated primarily at the pore boundaries, while some CA6 were adhered on the surface of Al2O3 particles. CA2 were mainly embedded around Al2O3 particles. The increase of CA6 and CA2 contents improved the flexural strength and porosity, and decreased the shrinkage rate. The Al2O3 ceramics with high flexural strength, high porosity and low shrinkage rate were successfully fabricated by adding 20 wt% CaCO3 with the particle size D90 below 7.8 µm. The resulting flexural strength and porosity were 8.9 MPa and 71.9%, respectively, representing an improvement of 21.9% and 19.8% compared to Al2O3 ceramics without CaCO3. Additionally, the shrinkage rate in the X (0.9%), Y (1.1%), and Z (1.5%) directions decreased significantly, and the corresponding reductions were 75.0%, 73.2%, and 74.1%, respectively.

Microzone characterization and corrosion resistance of water-based epoxysilane/Ti/Zr composite chemical conversion coating on multi-metals

A water-based epoxy silane and titanium/zirconium composite chemical conversion coating was prepared on the surfaces of 6061 aluminum alloy, 7075 aluminum alloy, and galvanized steel simultaneously. Our findings revealed that the composite chemical conversion coating exhibited the strongest anti-corrosion effect on multi-metals surfaces as the concentration of silane was 0.4 vol% and the conversion time was 90 s. The analysis showed that a notable deposition of TiO2 and ZrO2 in close proximity to intermetallic compounds, segregation phases enriched with copper, and inclusions. Notably, the formation of the composite chemical conversion coatings on the multi-metals surface primarily follows a synergistic mechanism involving adsorption, oxidation, and readsorption. Consequently, a crosslinked siloxane network structure is formed, which offers additional filling sites for surplus particles of Al2O3, TiO2, ZrO2, and Fe2O3.