Dispersed Al2O3 Research Articles

Effects of Sintering and Compress on Porosity, Mechanical Properties and Conductivity of Cu-Al<sub>2</sub>O<sub>3</sub> Composite Materials Fabricated by Mechano-Chemical Method

Nano Al2O3 dispersion - strengthened Cu-matrix composite materials were fabricated by mechano-chemical method. The method carries out at room temperature by mechanical milling in the attritor in 16h hours using the mixtures of CuO, Al and Cu powder ingredients, and then the mixtures were cold pressed into cylindrical samples and sintered at various temperatures (from 700°C to 900°C) and time (from 1 to 3 hours) in argon atmosphere. The XRD pattern and EDS results revealed that Al2O3 phases were formed and dispersed into Cu-matrix during mechano-chemical process. The Al peak disapeared at the end of mechano-chemical process and the final obtained products were Cu-Al2O3 composite materials with Al2O3 content of 3-10% volume. The SEM and EDS results also showed that the particle sizes of Al2O3 were in about (50÷100)nm and uniformly dispersed within the C-matrix. The porosity of materials strongly depends on pressure compress, sintering time and temperature. It decreases with increasing of these parameters and reaches about 5%. The porosity and Al2O3 content affected on mechanical properties of materials, such as micro-hardness and compress strength, due to the dispersion of nano-Al2O3 into Cu-matrix. The conductivity of materials decreases with increasing porosity and Al2O3 content.

Investigation of alumina nanofiller impact on the structural and dielectric properties of PEO/PMMA blend matrix-based polymer nanocomposites

Polymer nanocomposite (PNC) films have been prepared by the solution-cast method using a polymer blend of poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA) (PEO/PMMA = 50/50 wt%) as organic host matrix and x wt% Al2O3 nanoparticles (x = 0, 1, 3, and 5) as inorganic nanofiller. The morphological and structural behavior of these PNC films has been examined by employing the scanning electron microscope (SEM), X-ray diffractometer (XRD), and Fourier transform infrared (FTIR) spectrometer, whereas their dielectric polarization and relaxation processes are characterized by carrying out the dielectric relaxation spectroscopy (DRS) over the frequency range 2 × 101 to 1 × 106 Hz. Impact of Al2O3 nanofiller on the spherulite and porous morphology, degree of crystallinity, polymer-polymer and polymer-nanoparticle interactions, complex dielectric permittivity, ac electrical conductivity, and the polymers structural dynamics has been explored. It is revealed that initially 1 wt% dispersion of Al2O3 in the PEO/PMMA blend matrix significantly reduces the crystallinity and dielectric permittivity, and hinders the cooperative chain segmental dynamics of the polymers which unevenly changes with the further increase of Al2O3 concentration up to 5 wt%. The dielectric and electrical parameters of these materials have also been compared with the PNC materials based on other polar polymer host matrices containing different oxide inorganic nanoparticles. The results of this work provide a guideline to design and fabricate the alumina nanoparticles loaded flexible-type polymer nanodielectric materials for advanced technologies.

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.

200 MeV proton irradiation of the oxide-dispersion-strengthened copper alloy (GlidCop-Al15)

In search to identify extremely stable materials to perform the collimation function of the 7-TeV proton beam halo at the Large Hadron Collider (LHC), oxide dispersion strengthened (DS) copper alloys were explored. These internally oxidized copper alloys known as GlidCop are also leading candidates for high heat flux applications in fusion reactors and as divertor and first wall structure in ITER. These considerations have led to an extensive body of research on neutron-induced changes in the microstructure and physio-mechanical properties. This study focused primarily on the damage induced by 200 MeV protons on as wrought and cold-worked GlidCop Al15 DS copper ally selected as a candidate material of the LHC beam collimation structure to damage levels up to ∼10 displacements-per-atom (dpa) and irradiation temperatures up to ∼600 °C. For reference, low dose spallation neutron damage at sub-zero irradiation temperature was included in the study. Proton irradiation effects on dimensional stability, mechanical behavior, electrical resistivity and X-ray diffraction-based microstructural changes are presented in the paper. GlidCop Al15 exhibited excellent thermal stability and superior to pure Cu resistance to conductivity loss. Proton irradiation-induced hardening and embrittlement at distinct irradiation temperature regimes were shown to follow similar trends to what was reported under neutron exposure to even higher dpa damage. At Tirr ∼600 ± 20 °C the cold-worked DS copper alloy exhibited softening accompanied by elongation reduction while at Tirr ∼200 ± 10 °C the as-wrought experienced hardening with elongation increase. High resolution X-ray diffraction revealed that even low-dose neutron irradiation has a strong influence on the size and distribution of dispersed Al2O3 particles.

Effect of wet-rotating disc milling process for preparation of stable dispersed Al2O3 slurries and dense green bodies

Abstract A wet-rotating disc milling was used as a method to prepare ceramic slurry. The rheological measurements of the milled slurries showed that the apparent viscosity of the wet-rotating disc milled slurry was low and the slurry was nearly Newtonian behavior, whereas that of ball-milled slurry was more viscous and the slurry exhibited a very strong shear thinning effect. Furthermore, the internal structure composed of aggregated particles in the slurry of the ball-milled slurry was strong and fragile, whereas that of wet-rotating disc milled slurry was the soft structure due to good dispersion. Also, the relative densities of green compacts prepared by slip casting were measured by Archimedes’ method. The relative densities of green compact prepared by the wet-rotating disc milled slurries were higher than those of the ball-milled slurries, and were constant at around 65% without depending on the solids loading. The linear shrinkages of the sintered bodies prepared by ball-milled slurry increased from 14.2% to 21.2% with decreasing the solids loading of Al2O3 slurry. On the other hand, the linear shrinkages of sintered bodies prepared by wet-rotating disc milled slurries were constant at about 11%, resulting that the shrinkage of sintered body was suppressed by preparing well-dispersed and stable slurry with wet-rotating disc milling.

Fabrication, mechanical properties and electrical conductivity of Al2O3 reinforced Cu/CNTs composites

Copper is widely used in many applications due to its excellent electric conductivity, processing ductility and corrosion resistance. However, poor hardness and low strength are the major limitations of copper in many fields. Herein, we report a high-performance copper matrix composites prepared by powder metallurgy. The copper matrix composites were prepared by mixed acid treatment, molecular-level method, ball milling and spark plasma sintering (SPS) process. The fabrication, microstructure, mechanical properties and electrical conductivity of the composites were investigated. The results show that nano-Al2O3 can act as an active mixing agent to disperse CNTs in copper powders and increase the adhesion between CNTs and copper matrix in composites. Additionally, the uniform dispersion of Al2O3 and CNTs can restrict the grain growth and form a strong bonding interface. Thus, the synthesized Cu-1.5CNTs-0.5Al2O3 composite displays the highest comprehensive performance, such as 131 HV hardness, 345 MPa ultimate tensile strength, 324 MPa yield strength, 13.8% elongation, and 50.6 MS/m (87.2%IACS) electrical conductivity. This work provides a feasible way to prepare high-performance copper matrix composites.

Effect of laser-MIG hybrid welding on microstructure and properties of seismic steel plate for buildings

Abstract Single pass multi-layer welding tests were carried out on 10Ni5CrMoV steel plate for construction, the effects of welding energy input and welding speed on the microstructures, hardness and impact energy at −40 °C of 10Ni5CrMoV steel welded joints were studied. The results showed that, with the decrease of welding energy input and the increase of welding speed, the structure in the weld zone gradually transforms from granular bainite to martensite and a small amount of upper bainite, and the grain size in the coarse and fine grain areas in the heat affected zone gradually decreases, and the content of granular bainite decreases. The optimum welding process for 10Ni5CrMoV steel is welding energy input with 7.5 KJ/cm and welding speed with 1.25 m/min, at this time, the weld structure is granular bainite, acicular ferrite, a small amount of upper bainite and a small amount of martensite; The dispersed Al2O3, TiN or TiC composite phase formed during welding process can be used as nucleation core of ferrite, helpful to form acicular ferrite in the weld zone, and the welded joint of 10Ni5CrMoV steel has the best impact toughness.

Effects of thermal treatments on the residual stress and micro-yield strength of Al2O3 dispersion strengthened copper alloy

The microstructure, residual stress, and mechanical properties of a Cu-0.05wt%Al2O3 dispersion strengthened alloy in different treatment states were investigated. The alloy was cold forged with a reduction of 60%, followed by either normal annealing or creep annealing at 600 °C for 6 h. Compared with the cold forged alloy, the micro-yield strength and the residual stress of the creep annealed alloy were reduced by 8.2% and 80.3%, respectively. The significant decrease in residual stress after creep annealing could result from the elimination of voids and defects and the reduction of dislocation density in the sub-grains during heat treatment. The high micro-yield strength of the creep annealed alloy can be attributed to the well dispersed nano Al2O3 particles effectively pinning the sub-grain boundaries at the elevated temperature.

Interface strengthening and fracture behavior of multilayer TWIP/TRIP steel

Abstract Series of multilayer TWIP/TRIP steels were hot rolled at 1000 °C with different rolling reduction ratios of 25%, 50%, 60%, 70%, 80%, 90% and 94%, and some in-situ reacted Al2O3 whiskers were identified at the clad interface based on selection oxidation. The continuous oxidized films or walls were broken and separated into fine dispersed reinforcements with increasing rolling reduction ratio, which are beneficial to strengthen the interface and toughen the multilayer steels. At low rolling reduction ratio, the thick oxidation walls inhibit the grain growth and alloy element diffusion, leading to the weakness of interface bonding and interface delamination. However, at high rolling reduction ratio, the fine dispersed Al2O3 whiskers bridge the clad interface and induce grain crossing, resulting into strong interfaces and high uniform plastic deformation capacity. Moreover, the grain crossing phenomenon and inner TWIP/TRIP coordination deformation mechanism provide a novel approach for improving fracture elongation of multilayer steels.

Corrosion and Wear Characteristics of Electroless Ni–P, Ni–P–W and Composite Ni–P–W/Al2O3 Coatings on AZ91 Sheet

Electroless Ni–P–W was coated on AZ91 sheets with various W contents and both the corrosion and wear resistance characteristics of these coatings were observed. The increase in W content resulted in a decrease in P content and an increase in the crystallinity of the electroless coatings. The corrosion resistance of the electroless coatings increased upon increase in W content of the electroless coatings up to approximately 5%. Above this content, however, the corrosion resistance tended to decrease due to the disturbed grain structure of the electroless coating. But both the surface hardness and wear resistance increased concurrently due to the positive contribution of W solid solution hardening. The applied heat treatment resulted in a decrease in the corrosion resistance due to the disappearance of the amorphous structure and increase in both the surface hardness and wear resistance due to the precipitation hardening. Al2O3 dispersion was better with the nonionic surfactant, as compared to the anionic and cationic surfactants. Composite coating reduced the corrosion resistance and increased the wear resistance of the electroless Ni–P–W coatings. The applied heat treatment was observed to have positive contribution to Ni–P–W coatings in getting the optimum corrosion and wear resistance combination.

Influence of grain boundaries with dispersed nanoscale Al2O3 particles on the strength of Al for a wide range of homologous temperatures

The deformation and strengthening behavior of an ultra-fine grained (UFG) Al fabricated via powder metallurgy was investigated over a wide range of homologous temperatures (TH). Our results reveal that the presence of a high density of γ-Al2O3 nanoparticles, located primarily at high angle grain boundaries (HAGBs), promoted remarkable stabilization of the Al grain structure up to TH = 0.94. The 0.2% strain offset yield stress (YS0.2) of the materials annealed at 600 °C for 24 h with grain sizes (d3D) of 0.57, 1.67, 2.33 and 2.99 μm was systematically studied from room temperature (RT) to 600 °C. Our study reveals that with decreasing d3D the strain hardening ability of the materials gradually decreased, and this behavior became pronounced at elevated T, which was attributed to the onset of plastic instability. The YS0.2 of the materials at all T followed the relation YS0.2 = a + k d3D−0.5. As determined on the basis of data interpolation, a positive transition from an established Hall-Petch (HP) relation at RT occurred at d3D = ∼8 μm. As the parameter a was negative at RT and 300 °C the documented strength–structure relationship cannot be explained on the basis of a Hall-Petch relation. The γ-Al2O3 particles located at HAGBs did not contribute notably to RT strengthening, whereas GBs played a significant role in the overall strength. The materials showed a high YS0.2 up to a TH of 0.94. The YS0.2 was observed to be linearly correlated with the reciprocal square root of the d3D and the coefficient k followed k = 224.4–0.376 T relation. The HP model overestimated the YS0.2 values at elevated T namely for the materials with a smaller d3D. It is proposed that softening occurred as a result of the γ-Al2O3 particles densely distributed within a 3D network, which were included in Hansen's strengthening model; particle strengthening played a role at elevated T.

Dispersing Nanoparticles by Chiral Liquid Crystalline Elastomers for Performance Enhancement of Epoxy Nanocomposites

AbstractEpoxy nanocomposites with novel chiral side‐chain liquid crystalline elastomers (CSLCE) as dispersant grafted alumina (Al2O3) nanoparticles are prepared. The CSLCE are grafted onto the surface of Al2O3 by esterification, improving the dispersion of Al2O3 in organics. The side chain of CSLCE is composed of M1 containing a chiral mesogenic unit, a liquid crystal cross‐linking agent M2 containing a nematic mesogenic unit, and M3 containing carboxyl groups, which is because the structures can determine the characteristics of polymers. Optical rotation emerges via chiral mesogenic units in CSLCE, and the liquid crystal cross‐linking agent in the side chain causes the polymer to be linked into chains. The fracture toughness and thermal conductivity of Al2O3‐CSLCE/epoxy nanocomposites are significantly improved due to the good dispersion of Al2O3 nanoparticles in the epoxy and the synergistic interaction between Al2O3 and CSLCE. Meanwhile, the glass transition temperatures and thermal stability are enhanced.

Microstructure, Mechanical Properties and Wear Behavior of the Rheoformed 2024 Aluminum Matrix Composite Component Reinforced by Al2O3 Nanoparticles

The 2024 nanocomposite reinforced with Al2O3 nanoparticles was fabricated by the ultrasonic assisted semisolid stirring (UASS) method and rheoformed into a cylinder component. Microstructure, mechanical properties, and wear behavior of the rheoformed composite components were investigated. The results showed that the composite components with complete filling status and a good surface were rheoformed successfully. The deformation of semisolid slurries was mainly dominated by flow of liquid incorporating solid grains (FLS), sliding between solid grains (SSG), and plastic deformation of solid grains (PDS). Mechanical properties of the rheoformed composite components were influenced by stirring temperature, stirring time, and volume fraction of Al2O3 nanoparticles. The optimal ultimate tensile strength (UTS) of 358 MPa and YS of 245 MPa were obtained at the bottom of the rheoformed composite components after a 25-min stirring of composite semisolid slurry with 5% Al2O3 nanoparticles at 620 °C. Enhancement of mechanical properties was attributed to high density dislocations and dislocation tangles and uniform dispersed Al2O3 nanoparticles in the aluminum matrix. Natural ageing led to the occurrence of needle-like Al2CuMg phase and short-rod-like Al2Cu phase. UTS of 417 MPa and YS of 328 MPa of the rheoformed composite components were achieved after T6 heat treatment. Improvement of mechanical properties is due to the more precipitated needle-like Al2CuMg phase and short-rod-like Al2Cu phase. Wear resistance of the rheoformed composite components was higher than that of the rheoformed matrix component. Wear resistance of the rheoformed composite component increased with an increase in Al2O3 nanoparticles from 1% to 7%. A slight decrease in wear rate resulted from 10% Al2O3 nanoparticles due to greater agglomeration of Al2O3 nanoparticles. A combination mechanism of adhesion and delamination was determined according to worn surface morphology.

Heterogeneous microstructure of an Al2O3 dispersion strengthened Cu by spark plasma sintering and extrusion and its effect on tensile properties and electrical conductivity

Introducing coarse grains into nanocrystalline (NC) and ultrafine grained (UFG) metallic materials can lead to an excellent combination of strength and ductility. In this study, we produced Al2O3 dispersion-strengthened (Al2O3-DS) Cu with heterogeneous microstructure by mechanical alloying (MA) of Cu-Al2O3 powder mixture followed by spark plasma sintering (SPS) and hot extrusion (HE). For direct comparison, one sample was prepared by hot extrusion only without prior SPS of mechanically alloyed (MAed) powders. The microstructure of materials produced via a combination of SPS and HE possessed the heterogeneous microstructure consisting of Al2O3-free coarse grained (CG) Cu bands and Al2O3-rich UFG Cu regions. These different microstructural regions were found to play different roles on the tensile and electrical properties and their presence can be tuned to achieve desired mechanical and electrical properties. We also discuss the possible mechanisms responsible for the formation of the heterogeneous microstructure in the samples produced by a combined process of SPS and HE.

Fabrication of Al2O3 nano-micro patterns by Al2O3 dispersion resin using UV imprint lithography

Aluminum oxide (Al2O3) has excellent properties in terms of hardness, abrasion resistance, refractive index, electrical insulation and chemical stability; therefore, it has been used in various optical applications such as for resistance random access memory active layers and nano-micro polishing. In this study, a functional Al2O3 nanoparticle resin with refractive index control was developed and various nano-micro structures were formed using UV-nanoimprint lithography. It is also possible to adjust and measure the desired optical properties by controlling the specifications of the formed Al2O3 structures. It was confirmed that imprinting is possible not only on traditional rigid substrates but also on flexible ones. Furthermore, scanning electron microscopy showed that the various Al2O3 nano-micro structures were well formed. The effect of annealing temperature on the phase change and crystallinity was investigated by X-ray diffraction. The hardness and Young's modulus were also measured by using a nanoindenter. The refractive index of Al2O3 dispersion resin composition was examined using an ellipsometer. Moreover, the optical characteristics of each Al2O3 nano-micro structure were measured by UV–visible spectroscopy.

Annealing Effects on Microstructure and Mechanical Properties of Ultrafine-Grained Al Composites Reinforced with Nano-Al2O3 by Rotary Swaging

Microstructure evolution and variations in mechanical properties of Al-Al2O3 nanocomposite produced by powder metallurgy were investigated and compared with commercially pure aluminum (Al-1050) after furnace annealing. Fine gas-atomized Al powder compacts were first sintered in flowing nitrogen, subsequently consolidated into wires by rotary swaging and eventually annealed at 300 and 500 °C for 24 h each. Scanning and transmission electron microscopy with energy-dispersive spectroscopy was utilized to document the microstructure evolution. Rotary swaging was proven to lead to a marked decrease in grain size. After heavy swaging to true deformation degree of φ = 6 and annealing at 500 °C, obvious recrystallization was observed at Al-1050’s existing grain boundaries and the crystals began to grow perpendicular to the flow direction. In the Al-Al2O3 nanocomposite, fabricated from d50 = 6 μm Al powder, recrystallization partially occurred, while grains were still extremely fine. Due to the dual role of fine-grained Al2O3 dispersion strengthening, the nanocomposite showed improved mechanical performance in terms of tensile strength, approximately twice higher than Al-1050 after annealing at 500 °C.

Influence of the Procedure of Getting of a Highly Dispersed Additive on the Properties of Corundum Ceramics

We present the results of investigations of the process of sintering and the changes in the properties of corundum ceramics depending on the content and type of introduced highly dispersed Al2O3. The specimens are produced by the slip casting and sintered at various temperatures. It is shown that, for the other identical conditions, it is reasonable to use highly dispersed powders with spherical particles with an aim to improve the physicomechanical properties of corundum ceramics. In the production of dense ceramics, the shape of particles of highly dispersed powders does not have any significant influence on the decrease in the temperature of sintering.

Synthesis and luminescence properties of Al2O3@YAG: Ce core–shell yellow phosphor for white LED application

A monodispersed Al2O3@YAG: Ce core-shell phosphor has been synthesized by coating Y2O3: Ce film on Al2O3 particle. The phosphor has particles size of 60–120 nm and shows high dispersity due to the high dispersed Al2O3 particles prepared by nonaqueous precipitation method. The core-shell structured phosphor consists of a corundum core and a YAG shell. The Al2O3@YAG: Ce core-shell yellow phosphor presents high yellow emission. The light-emitting diode (WLED) based on this yellow phosphor and InGaN blue chip displays high white purity. This Al2O3@YAG: Ce core–shell phosphor can be viewed as a promising candidate yellow phosphor for white LEDs.

Melting enhancement of a latent heat storage with dispersed Cu, CuO and Al2O3 nanoparticles for solar thermal application

Abstract The performance of all latent heat storage system depends on the quality of phase change material used. In the present study, paraffin-based nanofluid dispersed with 5% of Cu, 5% of CuO and 5% of Al2O3 nanoparticles are used to investigate its effect on the storage characteristics. A 3-D numerical model of a shell and tube regenerative type latent heat storage is developed using®COMSOL Multiphysics 4.3a to predict the average temperature and melt fraction of paraffin-based nanofluid. The validation with the established pieces of literature and experiments indicated a sound agreement. The effect of adding nanoparticles on melting/solidification rate and energy storing/releasing rate are also studied. The result revealed that addition of 5% of Cu, 5% of Al2O3 and 5% of CuO nanoparticles improved the melting rate by 10 times, 3.46 times and 2.25 times and the discharged rate by 8 times, 3 times and 1.7 times, respectively compared to the pure paraffin filled latent heat storage system. However, it decreased the specific heat and heat of fusion which reduced the sensible and latent heat storing capacity. Additionally, orientations of cylinder and tube arrangement are also studied numerically using paraffin as phase change material.

Reaction of 1-(het)aryl-3-bromoprop-2-ynones with furans in solid metal oxides or salts: cross-coupling or cycloaddition?

1-(Het)aryl-3-bromoprop-2-ynones react with 2-(2-furyl)pyrrole in the Al2O3 or K2CO3 dispersion (room temperature, 1 h) to afford the cross-coupling products either at the furan or pyrrole rings. Furan and 2-methylfuran with 3-bromo-1-phenylprop-2-ynone under the same conditions give the Diels–Alder cycloadducts, while furan-2-carbaldehyde andits acetals are inactive.