The dynamic mechanical response of SiC particulate reinforced 2024 aluminum matrix composites

The compression properties of the aluminum alloy 2024 metal matrix composites reinforced with 50 vol.% SiC particles were investigated using Instron testing machine and split Hopkinson pressure bar (SHPB) in this paper. The compression stress–strain curves were obtained at the strain rates ranging from 1 × 10^− 3 to 2.5 × 10³/s. The fracture surfaces were characterized by scanning electron microscopy. The results showed that SiCp/2024 Al composites exhibited high strain-rate sensitivity. The strength of composites tended to increase–decrease with increasing of strain rates. The effect of the strain rate on elongation was also discussed.     

Structural and chemical characterization of precipitates in Al-2024/TiC composites

Structural characterizations based on transmission electron microscopy observations were carried out on as-fabricated and heat-treated Al-2024/TiC composites. These composites types reinforced with TiC particles were produced with a pressureless melt infiltration route at 1200 °C for 2 h under argon atmosphere. The composites were heat-treated at 530 °C during 150 min, cold-water quenched and subsequently artificial and natural aged at 190 °C for 12 h in an argon environment and at room temperature for 96 h, respectively. Different precipitate types were obtained and they were identified as CuAl₂, Al₃Ti, Ti₃AlC and Ti₃Al. Most of the precipitates were found to be uniformly distributed in the matrix and some regions show precipitates which have a cubic morphology (Ti₃Cu). High-resolution electron microscopy images were partially used for the characterization of the precipitates in these composites.     

Fe-based metallic glass particles reinforced Al-7075 matrix composites prepared by spark plasma sintering

Metallic glass (MG) reinforced aluminum matrix composites (AMCs) have attracted the interest of many researchers in the past few years. In this study, Fe₅₀Cr₂₅Mo₉B₁₃C₃ metallic glass (FMG) particles reinforced 7075 aluminum matrix (Al-7075) composites were prepared by spark plasma sintering (SPS) technique. The microstructure of the composites showed good interface bonding between the FMG particles and the matrix. The micro-hardness of the composite with 30 vol% FMG particles reached 160.63 HV, which was increased by 30% compared with that of Al-7075 (119.3 HV). The ultimate compression strength (UCS) of the composite was also improved significantly from 596 MPa for Al-7075 matrix to 749 MPa for the composite reinforced with 30 vol% FMG particles, and the compression strain of the composite reached 22%. These results indicate that the mechanical properties of the composites can be enhanced by adding high volume fraction FMG particles. The enhancement of the strength is resulted from multiple strengthening mechanisms, and the main contributions come from the thermal mismatch and grain refinement.     

Accumulative press bonding; a novel manufacturing process of nanostructured metal matrix composites

A new manufacturing process for metal matrix composites has been invented, namely accumulative press bonding (APB). The APB process provided an effective method to produce bulk Al/10 vol.% WC_p composite using tungsten carbide (WC) powder and AA1050 aluminum sheets as the raw materials. The microstructural evolutions and mechanical properties of the monolithic aluminum and Al/WC_p composite during various APB cycles were examined by scanning electron microscopy, X-ray diffractometry, X’pert HighScore software, and tensile test equipment. The results revealed that by increasing the number of APB cycles (a) the uniformity of WC particles in aluminum matrix improved, (b) the porosity of the composite eliminated, (c) the particle free zones decreased and (d) the cluster characteristics improved. Hence, the final Al/WC_p composite processed by 14 APB cycles showed a uniform distribution of WC_p throughout the aluminum matrix, strong bonding between particles and matrix, and a microstructure without any porosity and undesirable phases. The X-ray diffraction results also showed that nanostructured Al/WC_p composite with the average crystallite size of 58.4 nm was successfully achieved by employing 14 cycles of APB technique. The tensile strength of the composites enhanced by increasing the number of APB cycles, and reached to a maximum value of 216 MPa at the end of 14th cycle, which is 2.45 and 1.2 times higher than obtained values for annealed (raw material, 88 MPa) and 14 cycles APBed monolithic aluminum (180 MPa), respectively. Though the elongation of Al/WC_p composite lessened during the initial cycles of APB process, it increased at the final cycles of the mentioned process by 78%. Role of WC particles, uniformity of reinforcement, porosity, bonding quality of the reinforcement and matrix, grain refinement, and strain hardening were considered as the strengthening mechanisms in the manufactured composites.     

Precipitation strengthened high strength-conductivity copper alloys containing ZrC ceramics

Metal matrix composites (MMC) of copper and ZrC powders were prepared by the powder metallurgy route. Powders of both materials were introduced in stainless steel jag and mechanically mixed in a planetary mill under a protective atmosphere of argon during time ranging from 4 to 30 h. A characterization study of resulting powders indicated that a steady state particle distribution is developed after 12 h of milling. For this reason only these powders were consolidated by hot uniaxial pressing under 90 MPa at 923 K for 2 h. Residual porosity of these compacts was eliminated by rolling at 1073 K. Resulting materials present fine grained microstructure, tensile strength of 653 MPa and electrical conductivity up to 52% IACS. A detailed microstructural analysis by scanning and transmission electron microscopy showed not only ZrC particles but also the presence of very fine particles of carbides and oxides. WDX and EDX spectra of these particles revealed a high content of Fe and Cr for the carbides and Cu in the case of oxides.     

Characterization of oxide dispersion strengthened copper based materials developed by friction stir processing

The current study aims to show for the first time the ability of friction stir processing (FSP) in incorporating yttria particles into copper to produce an oxide dispersion strengthened material. The microstructure of the as-developed composites was characterized at various scales by light microscopy, electron probe microanalysis (EPMA) and scanning and transmission electron microscopy. The powder was found to be distributed in the Cu matrix as confirmed at various length scales from the micrometric to the nanometric level. The increase of the number of FSP passes leads to a more homogeneous and finer distribution of the particles as it favored the dissociation of the clusters of initial powder particles and the intergranular fracture of individual elemental particles. Transmission electron microscopy observations reveal that the constitutive crystallites of the initial powder, typically 10 nm in size, are frequently dissociated and dispersed into the copper matrix. In spite of their very low volume fraction, these 10 nm sized fragments which present the highest density among the various size classes of particles, exert a strengthening and work hardening effect.     

Microstructure and mechanical property of multi-walled carbon nanotubes reinforced aluminum matrix composites fabricated by friction stir processing

Aluminum matrix composites reinforced by different contents of multi-walled carbon nanotubes (MWCNTs) were fabricated by friction stir processing (FSP). The microstructure of nano-composites and the interface between aluminum matrix and MWCNTs were examined using optical microscopy (OM) and transmission electron microscopy (TEM). It was indicated that MWCNTs were well dispersed in the aluminum matrix throughout the FSP. Tensile tests and microhardness measurement showed that, with the increase of MWCNT content, the tensile strength and microhardness of MWCNTs/Al composites gradually increased, but on the contrary, the elongation decreased. The maximum ultimate tensile strength reached up to 190.2 MPa when 6 vol.% MWCNTs were added, and this value was two times more of that of aluminum matrix. Appearances and fracture surface micrographs of failed composite samples indicated that the composites become more and more brittle with the increase of the MWCNT content.     

Dry sliding tribological behavior and mechanical properties of Al2024–5 wt.%B4C nanocomposite produced by mechanical milling and hot extrusion

In this paper, tribological behavior and mechanical properties of nanostructured Al2024 alloy produced by mechanical milling and hot extrusion were investigated before and after adding B₄C particles. Mechanical milling was used to synthesize the nanostructured Al2024 in attrition mill under argon atmosphere up to 50 h. A similar process was used to produce Al2024–5 wt.%B₄C composite powder. The milled powders were formed by hot pressing and then were exposed to hot extrusion in 750 °C with extrusion ratio of 10:1. To study the microstructure of milled powders and hot extruded samples, optical microscopy, transmission electron microscopy and scanning electron microscopy (SEM) equipped with an energy dispersive X-ray spectrometer (EDS) were used. The mechanical properties of samples were also compared together using tension, compression and hardness tests. The wear properties of samples were studied using pin-on-disk apparatus under a 20 N load. The results show that mechanical milling decreases the size of aluminum matrix grains to less than 100 nm. The results of mechanical and wear tests also indicate that mechanical milling and adding B₄C particles increase strength, hardness and wear resistance of Al2024 and decrease its ductility remarkably.     

Mechanical properties of nanostructured Al2024–MWCNT composite prepared by optimized mechanical milling and hot pressing methods

Nanostructured Al2024–multiwall carbon nanotubes (MWCNTs) composites were produced using optimized mechanical milling and hot pressing methods. Nanostructured Al2024 powder was first prepared through 30 h mechanical milling of the alloy powder. MWCNTs up to 3 vol.% were added to the milled Al2024 powder and milled for different times. Differential thermal analysis (DTA) and X-ray diffraction (XRD) were used to assess the structural changes and thermal behavior during mechanical milling and hot pressing. Hardness and compression tests were applied on bulk samples to evaluate their mechanical properties. Mechanical milling applied on Al2024 powders for 30 h resulted in the grain refinement to ～30 nm. DTA analysis showed an endothermic peak at ～632 °C due to Al2024 melting and an exothermic peak between 645 and 658 °C related to Al and MWCNTs reaction. Mechanical milling of nanocomposite powder for 4 h and following hot pressing at 500 °C under a pressure of 250 MPa for 0.5 h were selected as optimized conditions for bulk nanocomposite preparation. With MWCNTs addition up to 2 vol.%, relative density remained at 98%, and hardness increased to 245 HV. Compressive strength of nanocomposites found a maximum value of 810 MPa at 2 vol.% MWCNTs addition which is 78%, 34% and 12% greater than that for Al2024–O, Al2024–T6 and nanostructured Al2024, respectively.     

Electromagnetic shielding effectiveness of aluminum alloy–fly ash composites

The cenosphere and precipitator fly ash particulates were used to produce two kinds of aluminum matrix composites with the density of 1.4–1.6 g cm⁻³ and 2.2–2.4 g cm⁻³ separately. The electromagnetic interference shielding effectiveness (EMSE) properties of the composites were measured in the frequency range of 30.0 kHz–1.5 GHz. The results indicated the EMSE properties of the two types of composites were nearly the same. By using the fly ash particles, the shielding effectiveness properties of the matrix aluminum have been improved in the frequency ranges 30.0 kHz–600.0 MHz and the increment varied with increasing frequency. The EMSE properties of 2024Al are in the range −36.1 ± 0.2 to −46.3 ± 0.3 dB while the composites are in the range −40.0 ± 0.8 to −102.5 ± 0.1 dB in the frequency range 1.0–600.0 MHz. At higher frequency, the EMSE properties of the composites are similar to that of the matrix. The tensile strength of the matrix aluminum has been decreased by addition of the fly ash particulate and the tensile strength of the composites were 110.2 MPa and 180.6 MPa separately. The fractography showed that one composite fractured brittly and the other fractured in a microductile manner.     

Effect of submicron size SiC particles on microstructure and mechanical properties of AZ31B magnesium matrix composites

The magnesium matrix composites reinforced with three volume fractions (3, 5 and 10 vol.%) of submicron-SiC particles (∼0.5 μm) were fabricated by semisolid stirring assisted ultrasonic vibration method. With increasing the volume fraction of the submicron SiC particles (SiCp), the grain size of matrix in the SiCp/AZ31B composites was gradually decreased. Most of the submicron SiC particles exhibited homogeneous distribution in the SiCp/AZ31B composites. The ultimate tensile strength and yield strength of the 10 vol.% SiCp/AZ31B composites were simultaneously improved. The study of interface between the submicron SiCp and the matrix in the SiCp/AZ31B composite suggested that submicron SiCp bonded well with the matrix without interfacial activity.     

Development of NiFe-CNT and Ni3Fe-CNT nanocomposites by mechanical alloying

NiFe-CNT and Ni₃Fe-CNT nanocomposites were fabricated by high energy mechanical alloying method. X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) and optical microscopy were employed for evolution of phase composition, morphology and microstructure of the powder particles. Ball milled powders were heat treated at 500 °C for 1 h to release the milling induced stresses. Bulk samples were prepared by sintering of cold pressed (300 MPa) samples at 1040 °C for 1 h. XRD patterns of powders, as-milled and after annealing at 500 °C did not show any peak related to CNTs or excess phases due to the interaction between CNTs and matrix. SEM micrographs showed that the addition of CNTs caused a reduction of powder particles size. The hardness value of as-milled NiFe and Ni₃Fe powders reach to 660 and 720 HV, respectively. According to optical microscopy evaluations, the amount and size of the porosities of the composites bulk samples decreased in comparison with matrix ones.     

An investigation of the synthesis,consolidation and mechanical behaviour of Al 6061 nanocomposites reinforced by TiC via mechanical alloying

Nanostructured Al 6061–x wt.% TiC (x = 0.5, 1.0, 1.5 and 2.0 wt.%) composites were synthesised by mechanical alloying with a milling time of 30 h. The milled powders were consolidated by cold uniaxial compaction followed by sintering at various temperatures (723, 798 and 873 K). The uniform distribution and dispersion of TiC particles in the Al 6061 matrix was confirmed by characterising these nanocomposite powders by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), differential thermal analysis (DTA) and transmission electron microscopy (TEM). The mechanical properties, specifically the green compressive strength and hardness, were tested. A maximum hardness of 1180 MPa was obtained for the Al 6061–2 wt.% TiC nanocomposite sintered at 873 K, which was approximately four times higher than that of the Al 6061 microcrystalline material. A maximum green compressive strength of 233 MPa was obtained when 2 wt.% TiC was added. The effect of reinforcement on the densification was studied and reported in terms of the relative density, sinterability, green compressive strength, compressibility and Vickers hardness of the nanocomposites. The compressibility curves of the developed nanocomposite powders were also plotted and investigated using the Heckel, Panelli and Ambrosio Filho and Ge equations.     

Evaluation of microstructure and mechanical properties of Al/Al2O3/SiC hybrid composite fabricated by accumulative roll bonding process

In this investigation, a new kind of metal matrix composites with a matrix of pure aluminum and hybrid reinforcement of Al₂O₃ and SiC particles was fabricated for the first time by anodizing followed by eight cycles accumulative roll bonding (ARB). The resulting microstructures and the corresponding mechanical properties of composites within different stages of ARB process were studied. It was found that with increasing the ARB cycles, alumina layers were fractured, resulting in homogenous distribution of Al₂O₃ particles in the aluminum matrix. Also, the distribution of SiC particles was improved and the porosity between particles and the matrix was decreased. It was observed that the tensile strength of composites improved by increasing the ARB passes, i.e. the tensile strength of the Al/1.6 vol.% Al₂O₃/1 vol.% SiC composite was measured to be about 3.1 times higher than as-received material. In addition, tensile strength of composites decreased by increasing volume fraction of SiC particles to more than 1 vol.%. Scanning electron microscopy (SEM) observation of fractured surfaces showed that the failure mechanism of broken hybrid composite was shear ductile rupture.     

Toughening performance of glass fibre composites with core–shell rubber and silica nanoparticle modified matrices

The fracture energies of glass fibre composites with an anhydride-cured epoxy matrix modified using core–shell rubber (CSR) particles and silica nanoparticles were investigated. The quasi-isotropic laminates with a central 0°/0° ply interface were produced using resin infusion. Mode I fracture tests were performed, and scanning electron microscopy of the fracture surfaces was used to identify the toughening mechanisms.The composite toughness at initiation increased approximately linearly with increasing particle concentration, from 328 J/m² for the control to 842 J/m² with 15 wt% of CSR particles. All of the CSR particles cavitated, giving increased toughness by plastic void growth and shear yielding. However, the toughness of the silica-modified epoxies is lower as the literature shows that only 14% of the silica nanoparticles undergo debonding and void growth. The size of CSR particles had no influence on the composite toughness. The propagation toughness was dominated by the fibre toughening mechanisms, but the composites achieved full toughness transfer from the bulk.     

Sol–gel derived nanoscale bioactive glass (NBG) particles reinforced poly(ε-caprolactone) composites for bone tissue engineering

This study investigated the effect of the addition of sol–gel derived nanoscale bioactive glass (NBG) particles on the mechanical properties and biological performances of PCL polymer, in order to evaluate the potential applications of PCL/NBG composites for bone tissue regeneration. Regardless of the NBG contents (10, 20, and 30 wt.%), the NBG particles, which were synthesized through the sol–gel process using polyethylene glycol (PEG) polymer as a template, could be uniformly dispersed in the PCL matrix, while generating pores in the PCL/NBG composites. The elastic modulus of the PCL/NBG composites increased remarkably from 89 ± 11 MPa to 383 ± 50 MPa with increasing NBG content from 0 to 30 wt.%, while still showing good ultimate tensile strength in the range of 15–19 MPa. The hydrophilicity, water absorption and degradation behavior of the PCL/NBG composites were also enhanced by the addition of the NBG particles. Furthermore, the PCL/NBG composite with a NBG content of 30 wt.% showed significantly enhanced in vitro bioactivity and cellular response compared to those of the pure PCL.     

Effect of a weak fiber interface coating in ZrB2 reinforced with long SiC fibers

This study reports the microstructural analysis and mechanical properties of a ZrB₂ ceramic containing long BN-coated Hi-Nicalon SiC fibers. A composite was produced and thoroughly characterized by transmission electron microscopy to study the interfaces at the nanoscale level. Full densification was accomplished by hot pressing at 1450 °C. The fiber in the sintered material retained its pristine aspect, confirming that the coating was effective in preventing degradation due to interactions with the matrix. Pull-out was observed on fractured surfaces, but toughness values were about 4.5 MPa√m, which was comparable to those of ZrB₂ materials with SiC additions in the form of particles or short fibers. However, the composites exhibited a controlled fracture behavior, as confirmed by a notably higher work of fracture, 140 J/m², compared with 20–30 J/m² of unreinforced ZrB₂ or ZrB₂ containing chopped fibers.     

Tensile properties of in situ synthesized (TiB + La2O3)/β-Ti composite

A novel (TiB + La₂O₃)/Ti-alloy composite was In situ synthesized through homogeneously melting in a non-consumable vacuum arc remelting furnace. Ti–35Nb–2Ta–3Zr β titanium alloy was chosen as the matrix Ti-alloy and different mass fractions of LaB₆ were chosen as additions. Microstructure observations were examined by optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscopy (TEM). The phase analysis was identified by X-ray diffraction (XRD). Largest ultimate tensile strength around 580 MPa and highest elongation around 30% is obtained in 0.1% LaB₆-additioned specimen. The appearance of too many La₂O₃ particles and the reduction of oxygen in the matrix alloy also attribute much to the strength and plasticity of (TiB + La₂O₃)/Ti composites. Lower ultimate tensile strength around 526 MPa is obtained in 0.5% LaB₆-additioned specimen.     

Effect of substrate surface roughening and cold spray coating on the fatigue life of AA2024 specimens

The effects of cold spray coating and substrate surface preparation on crack initiation under cyclic loading have been studied on Al2024 alloy specimens. Commercially pure (CP) aluminum feedstock powder has been deposited on Al2024-T351 samples using a cold-spray coating technique known as high velocity particle consolidation. Substrate specimens were prepared by surface grit blasting or shot peening prior to coating. The fatigue behavior of both coated and uncoated specimens was then tested under rotating bend conditions at two stress levels, 180 MPa and 210 MPa. Scanning electron microscopy was used to analyze failure surfaces and identify failure mechanisms. The results indicate that the fatigue strength was significantly improved on average, up to 50% at 180 MPa and up to 38% at 210 MPa, by the deposition of the cold-sprayed CP-Al coatings. Coated specimens first prepared by glass bead grit blasting experienced the largest average increase in fatigue life over bare specimens. The results display a strong dependency of the fatigue strength on the surface preparation and cold spray parameters.     

Production of TiC reinforced-aluminum composites with the addition of elemental carbon

TiC reinforced Al matrix composites were produced by the additions of elemental carbon to both Al + 4%Ti and Al + 5%Ti alloys. It is shown that the microstructure, phase composition as well as fracture behavior of the composites produced are controlled by the processing parameters, such as temperature, amount of excess carbon and duration. Composite microstructure subjected to 1300 °C for 15 min includes only TiC particles where the fracture occurs in a ductile manner whilst composites subjected to 1200 °C for 30 min contain Al₃Ti and TiC particles which show mixed mode of fracture behavior where Al₃Ti particles resulted in brittle fracture due to their coarser size.