Determining the effect of flake matrix size and Al2O3 content on microstructure and mechanical properties of Al2O3 nanoparticle reinforced Al matrix composites

In this study, Al2024 matrix composites reinforced with Al₂O₃ nanoparticle contents ranging from 1 to 5?wt% were produced via a new method called as flake powder metallurgy (FPM). The effect of flake size and Al₂O₃ nanoparticle content on the reinforcement distribution, microstructure, physical, and mechanical properties of the composites were studied. SEM analysis was performed to investigate the microstructure of metal matrix and the distribution of nanoparticles. The hot-pressed density increased with decreasing the matrix size. The hardness of the Al2024–Al₂O₃ nanocomposites fabricated by using fine matrix powders increased as compared to the Al2024–Al₂O₃ nanocomposites produced by using coarse matrix powders. It has been found that the FPM method proposed in this study revealed to be an effective method for the production of nanoparticle reinforced metal matrix composites.     

Fabrication of nano-sized Al2O3 reinforced casting aluminum composite focusing on preparation process of reinforcement powders and evaluation of its properties

In this study, a novel approach was used to fabricate Al₂O₃ nanoparticle reinforced aluminum composites to avoid agglomeration of nanoparticles in matrix. Al₂O₃ nanoparticles were separately milled with aluminum and copper powders at different milling durations and incorporated into A356 alloy via stir casting method. The effects of milling process and milling time on mechanical properties of the composites were evaluated by hardness, tensile, and compression tests. Based on the results, some of the composites, reinforced with Al₂O₃-metallic mixed powders, showed higher mechanical performance compared with that of the pure Al₂O₃ nanoparticle reinforced composite. This enhancement is related to uniform distribution of individual nanoparticles and grain refinement of A356 matrix, shown in microstructural studies. Moreover, the results showed that an increase in milling time, led to a gradual decrease in mechanical performance of the samples. It can be related to further oxidation of metallic powders that can act as inclusions and also further probable contamination of nanoparticles with increase in milling time. Studies on the fracture surfaces revealed that the failure of matrix was the basic mechanism of fracture in the composites. Agglomerated nanoparticles were observed on dendrites in the fracture surface of the Al₂O₃–Al reinforcement samples.     

Microstructure,mechanical properties and corrosion behaviour of Al–Si–Mg alloy matrix/zircon and alumina hybrid composite

In the present study, the effect of reinforcement on microstructure, mechanical properties and corrosion behaviour of aluminium–silicon–magnesium (Al–Si–Mg) alloy matrix hybrid composites reinforced with varying amounts of zircon and alumina has been investigated. Hardness and room temperature compressive tests were performed on Al–Si–Mg alloy as well as composites. Hardness and compressive strength was found to be higher for composites containing 3.75?% ZrSiO₄?+?11.25?% Al₂O₃. Similarly, Al–Si–Mg alloy and its composites were studied for corrosion behaviour in 1 N HCl corrosive media. The weight loss of all the composites was found to decrease with time due to the formation of passive oxide layer on the sample surface. The results obtained indicate that composites exhibit superior mechanical properties and corrosion resistance compared to unreinforced alloy.     

Effect of surface modification of Fe3O4 nanoparticles on thermal and mechanical properties of magnetic polyurethane elastomer nanocomposites

Magnetic polyurethane elastomer nanocomposites were prepared by incorporating pure and thiodiglycolic acid (TDGA) surface-modified Fe₃O₄ nanoparticles into polyurethane matrix using in situ polymerization method. Surface modification of Fe₃O₄ nanoparticles was carried out to enhance the dispersion of the nanoparticles in polyurethane matrix. Pure and TDGA surface-modified Fe₃O₄ nanoparticles were synthesized by coprecipitation method and characterized by Fourier Transform Infrared Spectroscopy, X-ray diffraction, and Vibrating Sample Magnetometer. The morphology and dispersion of the nanoparticles in the magnetic polyurethane elastomer nanocomposites were studied by Scanning Electron Microscope. It was observed that surface modification of Fe₃O₄ nanoparticles with TDGA enhanced the dispersion of the nanoparticles in polyurethane matrices. Furthermore, effect of surface modification of Fe₃O₄ nanoparticles on thermal and mechanical properties of magnetic polyurethane elastomer nanocomposite was investigated by thermogravimetric analysis, dynamic mechanical thermal analysis, and an Instron type Tensile Tester. It was concluded that surface modification of Fe₃O₄ nanoparticles allowed preparation of the magnetic nanocomposites with better mechanical properties. Moreover, study of fibroblast cells interaction with magnetic nanocomposites showed that the products can be a good candidate for biomedical application due to their in vitro biocompatibility and non-toxicity.     

Tribological properties of Al6061–Al2O3 nanocomposite prepared by milling and hot pressing

Tribological properties of bulk Al6061–Al₂O₃ nanocomposite prepared by mechanical milling and hot pressing were investigated. Al6061 chips were milled for 30 h to achieve a homogenous nanostructured powder. A 3 vol.% Al₂O₃ nanoparticles (∼30 nm) were added to the Al6061 after 15 and 30 h from the beginning of milling. The milling times with Al₂O₃ in these two samples were then 15 h and 30 min, respectively. Additionally, 3 vol.% Al₂O₃ (1 μm and 60 μm) was added to the Al6061 after 15 h of milling; where, the micron size Al₂O₃ in these two samples, was milled 15 h with the matrix. Hot pressing of milled samples was executed at 400 °C under 128 MPa pressure in a uniaxial die. The hot pressed samples were characterized by micro-hardness test, bulk density measurements, pin on disc wear test, and finally scanning electron microscopy observations. Fifteen hour-milled nanocomposite with nanoscale Al₂O₃, showed improvement in wear resistance and bulk density compared with that of 30 min-milled nanocomposites due to better dispersion of Al₂O₃ nanoparticles, improved surface quality of nanocomposite particles before pressing and more grain refinement of Al matrix. Moreover, increasing the reinforcement size increased the wear rate because of reduction in relative density, hardness and inter-particle spacing.     

Effect of alumina particle size and thermal condition of casting on microstructure and mechanical properties of stir cast Al–Al2O3 composites

Abstract

Metal matrix composites are considered as a distinct category of the advanced materials, which have low weight, high strength, high modulus of elasticity, low thermal expansion coefficient and high wear resistance. Among them, Al–Al₂O₃ composites have achieved significant attention due to their desired properties. In the present research, Al–Al₂O₃ composites with 5 vol.-% alumina were produced by stir casting at a temperature of 800°C. Two different particle sizes of alumina were used as 53–63 and 90–105 μm. The microstructure of the samples was evaluated by SEM. In addition, the mechanical properties of the samples were measured, and hence, the optimum temperature and particle size of alumina to be added to the Al matrix were determined. The results demonstrated the positive effect of alumina on improving the properties of Al–Al₂O₃ composites.     

Improving compressibility and thermal properties of Al–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> 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.     

Deposition of Al nanoparticles and their nanocomposites using a gas aggregation cluster source

The study describes the preparation and properties of Al/Al _x O _y nanoparticles and their nanocomposites with hydrocarbon plasma polymer. The nanoparticles were deposited using a simple gas aggregation cluster source based on a planar magnetron. The influence of deposition parameters on size distribution was studied. It was found that Al nanoparticles may be deposited with mean diameter ranging from 30 to 60 nm by varying magnetron current from 0.4 to 0.2 A. Attention was also paid to the investigation of the charge of the nanoparticles. It is shown that a large portion of Al _x O _y nanoparticles leave the gas aggregation source as negatively charged. The nanoparticles were also embedded into the plasma polymer matrix by their simultaneous co-deposition with plasma-polymerized n-hexane. Morphology and chemical composition of such fabricated nanocomposites were determined. It was shown that Al _x O _y nanoparticles embedded into the polymeric matrix exhibit localized surface plasmon resonances in the deep ultraviolet region of the electromagnetic spectrum and the position of the plasmon peak is strongly correlated with nanoparticle size.     

Superior high-temperature resistance of aluminium nitride particle-reinforced aluminium compared to silicon carbide or alumina particle-reinforced aluminium

Aluminium-matrix composites containing AlN, SiC or Al₂O₃ particles were fabricated by vacuum infiltration of liquid aluminium into a porous particulate preform under an argon pressure of up to 41 MPa. Al/AlN had similar tensile strengths and higher ductility compared to Al/SiC of similar reinforcement volume fractions at room temperature, but exhibited higher tensile strength arid higher ductility at 300–400 °C and at room temperature after heating at 600 °C for 10–20 days. The ductility of Al/AIN increased with increasing temperature from 22–400 °C, while that of Al/SiC did not change with temperature. At 400 °C, Al/AlN exhibited mainly ductile fracture, whereas Al/SiC exhibited brittle fracture due to particle decohesion. Moreover, Al/AlN exhibited greater resistance to compressive deformation at 525 °C than Al/SiC. The superior high-temperature resistance of Al/AlN is attributed to the lack of a reaction between aluminium and AlN, in contrast to the reaction between aluminium and SiC in Al/SiC. By using Al-20Si-5Mg rather than aluminium as the matrix, the reaction between aluminium and SiC was arrested, resulting in no change in the tensile properties after heating at 500 °C for 20 days. However, the use of Al-20Si-5Mg instead of aluminium as the matrix caused the strength and ductility to decrease by 30% and 70%, respectively, due to the brittleness of Al-20Si-5Mg. Therefore, the use of AIN instead of SiC as the reinforcement is a better way to avoid the filler-matrix reaction. Al/Al₂O₃ had lower room-temperature tensile strength and ductility compared to both Al/AlN and Al/SiC of similar reinforcement volume fractions, both before and after heating at 600 °C for 10–20 days. Al/Al₂O₃ exhibited brittle fracture even at room temperature, due to incomplete infiltration resulting from Al₂O₃ particle clustering.     

Physical, chemical, and mechanical properties of nanostructured materials

Nanocrystalline materials have special physical, chemical, and mechanical properties. To a significant extent, these properties are attributed to a high density of grain boundaries and other defects in nanocrystalline compounds. We study the microstructure and mechanical properties of nanomaterials (Al, Al-alloys, Cu, Ni, Ti, and stainless steel) and nanocomposites (Al₂O₃/Ni-P) by the methods of transparent and scanning electron microscopy, X-ray diffraction analysis, and microhardness and tensile tests. The experimental methods include the procedures of measuring the electric and corrosion resistances. The materials are prepared by using contemporary methods, namely, by hydrostatic extrusion (nanometals) and by sintering ceramic powders covered with Ni-P nanoparticles under high pressure by using the procedure of nonelectric chemical metallization (Al₂O₃/Ni-P nanocomposites). Published in Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 1, pp. 82–89, January–February, 2006.     

Mechanical and functional properties of ultrafine grained Al wires reinforced by nano-Al2O3 particles

A powder metallurgy route based on high-energy ball milling, powder consolidation by hot extrusion and cold rolling was used to produce Al composite wires reinforced with Al₂O₃ nanoparticles. The process was capable of preparing fully dense nanocomposites characterized by well dispersed nanoparticles in a ultra-fine grained matrix. Ball milling led to the fragmentation of the passivation oxide layer that covers the aluminum particles and of the alumina particle clusters added ex-situ in addition to embedding these nano-sized particles in the Al matrix and thus producing optimal precursors for subsequent consolidation. The nanocomposites showed improved mechanical performances in term of hardness and tensile strength. They also exhibited excellent damping behavior at high temperatures.     

Synthesis and characterisation of nanostructured Al–Al3V and Al–(Al3V–Al2O3) composites by powder metallurgy

In this study, the formation and characterisation of Aluminium (Al)-based composites by mechanical alloying and hot extrusion were investigated. Initially, the vanadium trialuminide (Al₃V) particles with nanosized structure were successfully produced by mechanical alloying and heat treatment. Al₃V–Al₂O₃ reinforcement was synthesised by mechanochemical reduction during milling of V₂O₅ and Al powder mixture. In order to produce composite powders, reinforcement powders were added to pure Al powders and milled for 5?h. The composite powders were consolidated in an extrusion process. The results showed that nanostructured Al-10?wt-% Al₃V and Al-10?wt-% (Al₃V–Al₂O₃) composites have tensile strengths of 209 and 226?MPa, respectively, at room temperature. In addition, mechanical properties did not drop drastically at temperatures of up to 300°C.     

Nano-sized aluminum oxide reinforced commercial casting A356 alloy matrix: Evaluation of hardness,wear resistance and compressive strength focusing on particle distribution in aluminum matrix

Achieving a uniform distribution of reinforcement within the matrix is a challenge which impacts directly on the properties and quality of the composite material. In the present study a fabrication and evaluation approach was used focusing on particle distribution in metal matrix. Al and Cu powders were separately milled with nano-Al₂O₃ particles and incorporated into A356 alloy via vortex method to produce cylindrical A356/nano-Al₂O₃ composites. The stirring was carried out in various durations. The variations of density, hardness, compressive strength, and wear resistance were measured throughout the cylindrical samples. The evaluation of mechanical properties and microstructural studies showed that an increase in stirring time led to a more uniform dispersion of particles in the matrix and also led to a decrease in mechanical properties due to an increase in porosity content of the composites compared with those of the samples stirred for shorter durations. Moreover, milling process affected particle distribution. Nanoparticles more uniformly dispersed in the Al₂O₃–Cu reinforced samples compared with that of the samples reinforced with Al₂O₃–Al or pure alumina powders.     

Evaluation of the fracture properties of polymer mortars reinforced with nanoparticles

Polymer-based nanocomposites have shown superior mechanical, thermal, as well as multifunctional properties when compared to plain polymer matrices. This fact has lead to a great research activity focused on incorporating polymeric materials with nanoparticles over the last years. The present research investigates the influence of nanoparticles reinforcement on fracture properties of polymer mortars, with particular regards to fracture and toughening mechanisms. This investigation was carried-out for a series of polymer mortars, containing varying amounts of aluminum oxide (Al₂O₃) and iron oxide (Fe₂O₃) nanoparticles dispersed in epoxy matrices.     

Effects of ball milling and high-pressure torsion for improving mechanical properties of Al–Al2O3 nanocomposites

Pure Al powders were mixed with a 30 % volume fraction of Al₂O₃ powders having particle sizes of ~30 nm. The mixed powders were first subjected to ball milling (BM) and thereafter consolidated by high-pressure torsion (HPT) at room temperature under a pressure of 3 GPa for 10 turns. The Al–Al₂O₃ composite produced by BM and HPT (BM + HPT) had a more uniform dispersion of the nano-sized Al₂O₃ particles in the Al matrix. Hardness values of the BM + HPT composites were higher than those of the composites without BM. It is shown that the use of BM powders for HPT is more effective in achieving a uniform dispersion of the nano-sized Al₂O₃ particles and in improving mechanical properties of the Al–Al₂O₃ nanocomposites.     

Microstructure,tensile and fatigue properties of AA6061/20 vol.%Al2O3p friction stir welded joints

Metal matrix composites reinforced with Al₂O₃ particles combine the matrix properties with those of the ceramic reinforcement, leading to higher stiffness and superior thermal stability with respect to the corresponding unreinforced alloys. However, their wide application as structural materials needs proper development of a suitable joining processes. The present work describes the results obtained from microstructural (optical and scanning electron microscopy) and mechanical evaluation (hardness, tensile and low-cycle fatigue tests) of an aluminium alloy (AA6061) matrix composite reinforced with 20 vol.% fraction of Al₂O₃ particles (W6A20A), welded using the friction stir welding process. The mechanical response of the FSW composite was compared with that of the base material and the results were discussed in the light of microstructural modifications induced by the FSW process on the aluminium alloy matrix and on the ceramic reinforcement. The FSW reduced the size of both particles reinforcement and aluminium grains and also led to overaging of the matrix alloys due to the frictional heating during welding. The FSW specimens, tested without any post-weld heat treatment or surface modification showed lower tensile strength and higher elongation to failure respect to the base material. The low-cycle fatigue life of the FSW composite was always lower than that of the base material, mainly at the lower strain-amplitude value. The cyclic stress response curves of the FSW composite showed evidence of progressive hardening to failure, at all cyclic strain-amplitudes, while the base material showed a progressive softening.     

Structural and morphological study of a 2024 Al–Al2O3 composite produced by mechanical alloying in high energy mill

2024 Al composite reinforced with Al₂O₃ particles was obtained by mechanical alloying (MA) using Al, Cu and Mg elemental powders as raw materials and Al₂O₃ nanoparticles as reinforcement. The results shown that as the MA time increased, the non-reinforced (WR) and Al₂O₃ reinforced powders (R1A and R2A) morphology changed from flake-flattened to equiaxed. Regarding the average particle size, WR group displayed a continuous decreasing value even for a processing time of 10 h while R2A and R1A groups shown a constant value for the same time. This led to the conclusion that steady state of the process was reached in shorter times in presence of Al₂O₃ nanoparticles. It was found that the reinforcement was present in the matrix like isolated particles and small agglomerates which affected the dislocation motion, and it was assumed that this fact caused the increase observed in the microhardness values. There was no evidence of new phase precipitation through MA process.     

Effect of 10Ce-TZP/Al2O3 nanocomposite particle amount and sintering temperature on the microstructure and mechanical properties of Al/(10Ce-TZP/Al2O3) nanocomposites

A zirconia/alumina nanocomposite stabilized with cerium oxide (Ce-TZP/Al₂O₃ nanocomposite) can be a good substitute as reinforcement in metal matrix composites. In the present study, the effect of the amount of 10Ce-TZP/Al₂O₃ particles on the microstructure and properties of Al/(10Ce-TZP/Al₂O₃) nanocomposites was investigated. For this purpose, aluminum powders with average size of 30 μm were ball-milled with 10Ce-TZP/Al₂O₃ nanocomposite powders (synthesized by aqueous combustion) in varying amounts of 1, 3, 5, 7, and 10 wt.%. Cylindrical-shape samples were prepared by pressing the powders at 600 MPa for 60 min while heating at 400–450 °C. The specimens were then characterized by scanning and transmission electron microscopy (SEM and TEM) in addition to different physical and mechanical testing methods in order to establish the optimal processing conditions. The highest compression strength was obtained in the composite with 7 wt.% (10Ce-TZP/Al₂O₃) sintered at 450 °C.     

Epoxy nanocomposites - fracture and toughening mechanisms

This study focuses to provide information about reinforcing influences of nanoparticles exerted on the mechanical and fracture mechanical properties of epoxy resins, particularly with regard to fracture and toughening mechanisms. A comprehensive study was carried out on series of nanocomposites containing varying amounts of nanoparticles, either titanium dioxide (TiO₂) or aluminium oxide (Al₂O₃). Nanocomposites were systematically produced by applying high (shear) energy during a controlled dispersion process, in order to reduce the size of agglomerates and to gain a homogeneous distribution of individual nanoparticles within the epoxy resin. The mechanical performance of the nanocomposites was then characterized by flexural testing, dynamic mechanical analysis (DMA), and furthermore, by fracture mechanics approaches (LEFM) and fatigue crack growth testing (FCP). The microstructure of specimens and the corresponding fracture surfaces were examined by TEM, SEM and AFM techniques in order to identify the relevant fracture mechanisms involved, and to gain information about the dispersion quality of nanoparticles within the polymer. It was found that the presence of nanoparticles in epoxy induces various fracture mechanisms, e.g. crack deflection, plastic deformation, and crack pinning. At the same time, nanoparticles can overcome the drawbacks of traditional tougheners (e.g. glass beads or rubber particles) by simultaneously improving stiffness, strength and toughness of epoxy, without sacrificing thermo-mechanical properties.     

Fabrication and characterisation of copper–alumina nanocomposites prepared by high-energy fast milling

Two different methods are used to prepare Cu–20 vol-% Al₂O₃ nanocomposite powders via high-energy planetary fast milling. In the solid solution method, CuO powder was added to the Cu–Al solid solution powder, and the composite was fabricated by milling after 100?h. In the direct mixing method, Cu and Al₂O₃ powders were mechanically milled via high-energy planetary fast milling for 100?h. The transition electron micrographs (dark and white fields) revealed the presence of Al₂O₃ nanoparticles in crystalline Cu matrices for both methods. However, the density and bending strength of the nanocomposites produced via the solid solution method were higher than those of the samples produced via the direct mixing method.