Synthesis and characterization of titanium-45S5 Bioglass nanocomposites

Titanium-45S5 Bioglass nanocomposites were synthesized by the combination of mechanical alloying and powder metallurgy process. The structure, mechanical and corrosion properties of these materials were investigated. Microhardness test showed that the obtained material exhibits Vicker’s microhardness as high as 770 HV_0.2 for Ti-20 wt.% 45S5 Bioglass, which is more than three times higher than that of a conventional microcrystalline titanium (225 HV_0.2). Additionally, titanium-10 wt.% of 45S5 Bioglass nanocomposites (i_c = 1.20 × 10⁻⁷ A/cm², E_c = −0.42 V vs. SCE) were more corrosion resistant than microcrystalline titanium (i_c = 2.27 × 10⁻⁶ A/cm², E_c = −0.36 V vs. SCE). In vitro biocompatibility of these materials was evaluated and compared with a conventional microcrystalline titanium, where normal human osteoblast (NHOst) cells from Cambrex (CC-2538) were cultured on the disks of the materials and cell growth was examined. The morphology of the cell cultures obtained on Ti-10 wt.% 45S5 Bioglass nanocomposite was similar to those obtained on the microcrystalline titanium. Mechanical alloying and powder metallurgy process for the fabrication of titanium-45S5 Bioglass nanocomposites with a unique microstructure, higher hardness, lower Young’s modulus and better corrosion resistance, in comparison to microcrystalline titanium, were developed. On the other hand, Ti-10 wt.% 45S5 Bioglass composites posses higher fracture toughness compared to 45S5 Bioglass. The proper modification of chemical composition and microstructure of Ti-bioceramic nanocomposites can expand the use of titanium in the biomedical fields.     

A new approach to joining of bulk copper using microwave energy

Metallurgical joining of high thermal conductivity materials like copper has been technically challenging. This paper illustrates a novel method for joining of bulk metallic materials through microwave heating. Joining of copper in bulk form has been carried out using microwave energy in a multimode applicator at 2.45 GHz and 900 W. Charcoal was used as susceptor material to facilitate microwave hybrid heating (MHH). Copper in coin and plate forms have been successfully joined through microwave heating within 900 s of exposure time. A sandwich layer of copper powder with approximately 0.5 mm thickness was introduced between the two candidate surfaces. Near complete melting of the powder particles in the sandwich layer does take place during the microwave exposure leading to metallurgical bonding of the bulk surfaces. Characterisation of the joints has been carried out through microstructure study, elemental analysis, phase analysis, microhardness survey, porosity measurement and tensile strength testing. X-ray diffraction (XRD) pattern indicates that some copper powder particles got transformed into copper oxides. XRD analysis also reveals that the dominant orientation (3 1 1) in starting copper powder got transformed into a preferential orientation (1 1 1) in the joint. A dense uniform microstructure with good metallurgical bonds between the sandwich layer and the interface was obtained. The hardness of the joint area was observed to be 78 ± 7 Hv, while the porosity in the joint was observed to be 1.92%. Strength character of the copper joints shows approximately 29.21% elongation with an average ultimate tensile strength of 164.4 MPa.     

Effects of copper and Al2O3 particles on characteristics of Cu–Al2O3 composites

High-energy milling was used for production of Cu–Al₂O₃ composites. The inert gas-atomized prealloyed copper powder containing 2 wt.%Al and the mixture of the different sized electrolytic copper powders with 4 wt.% commercial Al₂O₃ powders served as starting materials. Milling of prealloyed copper powders promotes formation of nano-sized Al₂O₃ particles by internal oxidation with oxygen from air. Hot-pressed compacts of composites obtained from 5 and 20 h milled powders were additionally subjected to the high-temperature exposure in argon at 800 °C for 1 and 5 h. Characterization of processed material was performed by optical and scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), microhardness, as well as density and electrical conductivity measurements. Due to nano-sized Al₂O₃ particles microhardness and thermal stability of composite processed from milled prealloyed powders are higher than corresponding properties of composites processed from the milled powder mixtures. The results were discussed in terms of the effects of different size of starting copper powders and Al₂O₃ particles on the structure, strengthening of copper matrix, thermal stability and electrical conductivity of Cu–Al₂O₃ composites.     

High-strength and highly-uniform composites produced by compocasting and cold rolling processes

Silicon carbide reinforced aluminum alloy composite materials produced by casting methods are increasingly used in many engineering fields. However, these materials suffer from poor distribution of the reinforcement particles in the matrix and high content of porosity. The effect of subsequent cold rolling process with different reductions on the porosity, microstructure and mechanical properties of cast Al6061/10 vol.% SiC_p composite was investigated in this study. Composites fabricated by compocasting method were rolled at five different reductions of 30, 60, 75, 85 and 95%. The rolled specimens exhibited reduced porosity as well as a more uniform particle distribution when compared with the as-cast samples. Microscopic investigations of the composites after 95% reduction showed an excellent uniform distribution of silicon carbide particles in the matrix. During cold rolling process it was observed that the tensile strength and ductility of the samples increased by increasing the reduction content. After 95% reduction, the tensile strength and elongation values reached 306.7 MPa and 7.9%, which were 4.6 and 3.3 times greater than those of the as-cast composite, respectively.     

Nanostructured TiC-TiB2 composites obtained by adding carbon nanotubes into the self-propagating high-temperature synthesis process

The synthesis of nanostructured TiC-TiB₂ by self-propagating high-temperature synthesis (SHS) has been investigated by using carbon nanotubes as precursor materials in partial substitution of graphite according to the following reaction: 6Ti + B₄C + (3−x)C + x CNT → 4TiC + 2TiB₂.Different amounts of CNTs addition have been studied in order to achieve structural refinement of the SHS products. The CNT molar content was varied in order to define the optimal composition, which allows to obtain nanostructured TiC-TiB₂ powders morphologically homogenous.The optimized composition has been chosen for the further densification step. The Pressure Assisted Fast Electric Sintering (PAFES) technique gave bulk composites with ultrafine grained microstructure. The mechanical characterization showed very high hardness and good fracture toughness values if compared to literature data.     

Highly porous polycaprolactone-45S5 Bioglass® scaffolds for bone tissue engineering

Highly porous biocompatible composites made of polycaprolactone (PCL) and 45S5 Bioglass® (BG) were prepared by a solid–liquid phase separation method (SLPS). The composites were obtained with BG weight contents varying in the range 0–50%, using either dimethylcarbonate (DMC) or dioxane (DIOX) as solvent, and ethanol as extracting medium. The porosity of the scaffolds was estimated to be about 88–92%. Mechanical properties showed a dependence on the amount of BG in the composites, but also on the kind of solvent used for preparation, composites prepared with DIOX showing enhanced stress at deformation with respect to composites prepared with DMC (stress at 60% of deformation being as high as 214 ± 17 kPa for DIOX-prepared composites and 98 ± 24 kPa for DMC-prepared ones, with 50 wt/wt_PCL% of glass), as well as higher elastic modulus (whose value was 251 ± 32 kPa for DIOX-prepared scaffolds and 156 ± 36 kPa for DMC-prepared ones, always with 50 wt/wt_PCL% of glass). The ability of the composites to induce precipitation of hydroxyapatite was positively evaluated by means of immersion in simulated body fluid and the best results were achieved with high glass amounts (50 wt/wt_PCL%). In vitro tests of cytotoxicity and osteoblast proliferation showed that, even if the scaffolds are to be considered non-cytotoxic, cells suffer from the scarce wettability of the composites.     

Mullite and alumina composites preparation from cordierite and aluminium hydroxide

Densification and phase transformation of mullite and alumina composites prepared from cordierite and aluminium hydroxide mixture were investigated. X-ray diffraction revealed the presence of mullite since the early stage of aluminium hydroxide addition to the cordierite. Above 40 wt.% of aluminium hydroxide addition, the presence of spinel and mullite phases can be detected by X-ray diffraction and confirmed by X-ray photoelectron spectroscopy. The X-ray photoelectron spectroscopy analysis showed that the amounts of spinel as well as mullite present increased with increasing aluminium hydroxide concentration at the expense of cordierite. These analyses were completed by density measurements and scanning electron microscopy observation.     

Impact of carbon black substitution with nanoclay on microstructure and tribological properties of ternary elastomeric composites

Various particulate composites based on epoxidised natural rubber (ENR), carbon black (CB), and nanoclay (NC) were prepared keeping the total filler content constant at 35 phr (parts per 100 g rubber). Tribology and hysteretic (stress–strain) properties of the composites were analyzed. Morphology of these composites were also characterized by small angle X-ray scattering (SAXS), transmission electron microscopy (TEM), scanning electron microscopy (SEM) to establish the structure–property correlations. SAXS results reveal enhancement in overall interfacial roughness (ds) with the increased substitution of CB by NC. Increased CB–NC interface causes enhancement in ds, leading to reduction in wear resistance of ternary composites. Reduction of wear resistance for NC populated samples is attributed to lower dispersion parameter (D_0,1) values of NC in the matrix, realized through image analysis of TEM photomicrographs. Thus, for ternary particulate samples, a definite interrelation among the extent of wear, ds and D_0,1 is realized. Frictional force (F_T) and its adhesive component (F_A) increase when CB is substituted by NC up to 15 phr. When NC fraction exceeds 15 phr, both F_T and F_A decrease substantially. This is attributed to the lubricity offered by the modified NC at higher NC concentration, which is explained using a predictive mechanism.     

The effect of crosslinker on mechanical and morphological properties of tropical wood material composites

In this study, wood polymer composites (WPCs) based on five kinds of selected tropical wood species, namely Jelutong (Dyera costulata), Terbulan (Endospermum diadenum), Batai (Paraserianthes moluccana), Rubber (Hevea brasiliensis), and Pulai (Alstonia pneumatophora), were impregnated with methyl methacrylate (MMA) and hexamethylene diisocyanate (HMDIC) monomers mixture in the ratio of 1:1 for composite manufacturing. All these tropical wood reacted with hexamethylene diisocyanate and crosslinked with MMA which enhanced the hydrophobic (restrained water) nature of wood. The vacuum-pressure method was used to impregnate the samples with monomer mixture. The monomer mixture loading achievable was found to be dependent on the properties of wood species. Low loading was observed for the high density wood species. Mechanical strength of fabricated wood polymer composites (WPCs) in term of modulus of elasticity (MOE) and modulus of rupture (MOR) were found to be significantly improved. The wood–polymer interaction was confirmed by Fourier transform infrared (FTIR) spectroscopy. Morphological properties of raw wood and WPC samples were evaluated by scanning electron microscopy (SEM) and XRD analysis and an improvement in morphological properties was also observed for WPC.     

Natural fibre-reinforced composites for bioengineering and environmental engineering applications

Recently, the mankind has realized that unless environment is protected, he himself will be threatened by the over consumption of natural resource as well as substantial reduction of fresh air produced in the world. Conservation of forests and optimal utilization of agricultural and other renewable resources like solar and wind energies, and recently, tidal energy have become important topics worldwide. In such concern, the use of renewable resources such as plant and animal based fibre-reinforce polymeric composites, has been becoming an important design criterion for designing and manufacturing components for all industrial products. Research on biodegradable polymeric composites, can contribute for green and safe environment to some extent. In the biomedical and bioengineered field, the use of natural fibre mixed with biodegradable and bioresorbable polymers can produce joints and bone fixtures to alleviate pain for patients. In this paper, a comprehensive review on different kinds of natural fibre composites will be given. Their potential in future development of different kinds of engineering and domestic products will also be discussed in detail.     

Effect of long-term service exposure on microstructure and mechanical properties of Alloy 617

The present work was carried out to investigate the effect of long-term service exposure on microstructure and mechanical properties of a gas turbine hot gas path component, made of Alloy 617. The results showed significant service-induced microstructural changes, such as excessive grain boundary Cr-rich M₂₃C₆ carbides formation and some oxidation features in the exposed material in compare with the solution-annealed material. Also it was found that the yield strength and hardness of the alloy have increased while the ductility of the alloy has decreased. In the similar test conditions, the stress-rupture life of the exposed alloy decreased considerably compared to the solution-annealed sample, which could be attributed to the microstructural degradation, especially formation of continuous M₂₃C₆ carbides on grain boundaries.     

Microstructural development during transient directional solidification of hypermonotectic Al–Bi alloys

Directional unsteady-state solidification experiments were performed with hypermonotectic Al–5.0 wt%Bi and 7.0 wt%Bi alloys. Thermal parameters such as the growth rate (v) and the thermal gradient (G) were experimentally determined by cooling curves recorded along the casting length. The predominant Bi-rich phase was characterized by droplets embedded in the aluminum matrix. Both the interphase spacing (λ) and the Bi-rich particles diameter (d) were measured along the casting length. These microstructural features were correlated to the solidification thermal parameters: growth rate, cooling rate and thermal gradient. An experimental law expressing λ as a function of both G and v was found to better represent the growth of hypermonotectic Al–Bi alloys. Moreover, it was found that the interphase spacing decreases with increasing alloy bismuth content.     

Effects of sintering parameters on the microstructure and tensile properties of in situ TiBw/Ti6Al4V composites with a novel network architecture

In order to better understand the relationship of processing–structure–mechanical properties of in situ TiB whisker reinforced Ti6Al4V (TiBw/Ti64) composites with a novel network architecture, the effects of sintering parameters on the microstructure and tensile properties of the composites were investigated. TiB whiskers with the highest aspect ratio and the coarsest whiskers were obtained at 1100 °C and 1200 °C due to the skips of whisker growth speeds along the [0 1 0] direction and the [0 0 1] and [1 0 0] directions, respectively. Additionally, TiB whisker with a claw-like structure can be synthesized from one TiB₂ polycrystal parent. The quasi-continuous network architecture of TiBw/Ti64 composites can be achieved at higher sintering temperatures more than 1200 °C. The prepared composites with the quasi-continuous network architecture exhibit a superior combination of tensile properties.     

Influence of cobalt phase on thermal shock resistance of Al2O3-TiC composites evaluated by indentation technique

Cobalt-coated Al₂O₃ and TiC powders were prepared using an electroless method to improve resistance to thermal shock. The mixture of cobalt-coated Al₂O₃ and TiC powders (about 70 wt.% Al₂O₃-Co + 30 wt.% TiC-Co) was hot-pressed into an Al₂O₃-TiC-Co composite. The thermal shock properties of the composite were evaluated by indentation technique and compared with the traditional Al₂O₃-TiC composite. The composites containing 3.96 vol.% cobalt exhibited better resistance to crack propagation, cyclic thermal shock and higher critical temperature difference (ΔT_c). The calculation of thermal shock resistance parameters (R parameters) shows that the incorporation of cobalt improves the resistance to thermal shock fracture and thermal shock damage. The thermal physic parameters are changed very little but the flexure strength and fracture toughness of the composites are improved greatly by introducing cobalt into Al₂O₃-TiC (AT) composites. The better thermal shock resistance of the composites should be attributed to the higher flexure strength and fracture toughness.     

Nanoindentation study of magnetron-sputtered CrN and CrSiN coatings

CrN and CrSiN coatings were deposited on stainless steel substrate by reactive magnetron sputtering. The coatings were characterized for phases, chemical composition, microstructure, and mechanical properties by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM)/energy dispersive spectroscopy (EDS), atomic force microscopy (AFM), and nanoindentation technique, respectively. The cubic phase was the only phase observed in both the coatings as observed in XRD results. A dense morphology was observed in these coatings deposited with high nitrogen and Si contents, 50:50 and 18.65 at.%, respectively. Nanoindentation measurement of CrN coatings, with Ar + N₂ proportions of 60:40, showed maximum hardness (H) and modulus (E) of 21 ± 0.85 GPa and 276 ± 13 GPa, respectively. The CrN coatings deposited in pure N₂ atmosphere showed H and E values of 27 ± 1.62 and 241 ± 10 GPa, respectively. The measured H and E values of CrSiN coatings were found to be 28 ± 1.40 GPa and 246 ± 10 GPa, respectively. The improved hardness in both the coatings was attributed mainly to a reduction in crystallite size, decrease in surface roughness, and dense morphology. The incorporation of Si into the CrN coatings has improved both hardness and Young’s modulus.     

Effect of extrusion ratio on mechanical and corrosion properties of AZ31B alloys prepared by a solid recycling process

Some AZ31B magnesium alloy bars were prepared by a solid recycling process with different extrusion ratios. A reference specimen was processed by extruding an as-received AZ31 ingot. The microstructures, mechanical and corrosion properties of AZ31B magnesium recycled specimens were investigated. With increasing extrusion ratio, the yield strength, tensile strength and yield ratio increases. The reliability of the recycled alloy is poorer than the reference specimen. The corrosion rates of recycled AZ31B magnesium specimens increase immersed in both alkaline and neutral 4% NaCl solution with a decrease extrusion ratio. The corrosion resistance of recycled AZ31B magnesium specimens is improved with increasing pH of immersed solution. The recycled specimens show superior corrosion resistance than reference specimen.     

Effects of applied pressure on microstructure and mechanical properties of squeeze cast ductile iron

In this study, the effects of applied pressure during solidification on the microstructure and mechanical properties of cylindrical shaped ductile iron castings were investigated. Magnesium treated cast iron melts were solidified under atmospheric pressure as well as 25, 50 and 75 MPa external pressures. Microstructure features of the castings were characterized using image analysis, optical microscopy, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) techniques. Tensile properties, toughness and hardness of the castings were also measured. The results showed that average graphite nodule size, free graphite content and ferrite content of the castings decreased and pearlite and eutectic cementite contents increased as the applied pressure was raised from 0 to 75 Mpa. Graphite nodule count was first increased by raising the applied pressure up to 50 MPa and then decreased. The highest graphite nodule count was obtained at 50 MPa applied pressure. The microstructural changes were associated with the improved cooling rate and the expected changes in the corresponding phase diagram of the alloy under pressure. The ultimate tensile strength (UTS), yield point strength (0.2% offset) and fracture toughness of the castings were improved when the applied pressure was raised from 0 to 50 MPa. Further increase of the applied pressure resulted in slight decrease of these properties due to the formation of more cementite phase in structures as well as reduced graphite nodule count. Hardness of the castings continuously increased with increasing the applied pressure.     

Aramid/epoxy composites sandwich structures for low-observable radomes

Low-observable radomes are usually made of E-glass/epoxy composite due to its low dielectric constant which is necessary not to interfere electromagnetic (EM) wave transmission characteristics. Since aramid fibers have lower dielectric constant and higher strength than those of E-glass fiber, aramid fiber radome structures may have better the EM transmission and mechanical characteristics than those of E-glass/epoxy radomes. In this work, the low-observable radome was constructed with a sandwich construction composed of aramid/epoxy composites faces, foam core and Frequency Selective Surface (FSS) which had the abilities of transmitting EM waves selectively in the X-band range. The EM wave transmission characteristics of the low-observable radome were simulated by a 3-dimensional electromagnetic analysis software and also measured by the free space measurement method with respect to the pattern size of FSS and foam cores. The mechanical properties of the low-observable radome made of aramid/epoxy composite were measured by the 3-point bending test and compared to those of the conventional low-observable radome made of E-glass/epoxy composite.     

Preparation of graphene nanosheet/alumina composites by spark plasma sintering

Graphene nanosheet/alumina composite has been prepared by spark plasma sintering. A homogeneous distribution of nanosheets in an alumina matrix could be obtained by the electrostatic attraction between graphite oxide and alumina particles and their subsequent reduction. The introduction of graphene nanosheet leads to refinement of grain size of alumina after hot pressing. The experimental results have shown that the fracture toughness and conductivity of the graphene nanosheet/alumina composite are about 53% and 13 orders of magnitude higher than those of unreinforced alumina material, respectively.     

Post-impact behaviour of aerospace composites for high-temperature applications: experiments and simulations

The post-impact performance of different carbon-fabric-reinforced composite materials were studied experimentally and analytically. Three types of thermosetting matrix were considered: conventional epoxy, high-temperature curing epoxy and epoxy-isocyanate. Experimental testing consisted of impacting rectangular specimens at different energy levels by using a spring-driven impact apparatus that was able to impart velocities of up to 5 m s⁻¹ to masses of 0.5, 1.0, 2.5 and 5.0 kg travelling horizontally. After impact, coupons were non-destructively inspected by means of opaque-enhanced dye-penetrant X-radiography and tested in static compression to correlate impact energy, damage extent and residual strength. Epoxy composites contain damage within a narrow region, while epoxy-isocyanate materials propagate the damage far away from impact point. Epoxy composites show an asymptotically decreasing failure strength with impact energy up to a lower threshold (0.3–0.4 times that of the undamaged material), while epoxy-isocyanate material shows a trend of ever decreasing residual strength. An analytical study was performed by means of the finite element code PAM-FISS, used to simulate the compression-after-impact (CAI) tests. Type, size and location of damage, as well as the mechanisms leading to final failure, were reproduced quite well by the finite element analysis (FEA), while some discrepancies between FEA and experimental CAI residual strength tests were found (7% for undamaged specimens and 10% for blister-delaminated specimens); higher errors were found in the case of completely delaminated specimens, mainly owing to the inability of the present software and hardware to conveniently model the complete state of damage.