Preparation and tribological performance of chemically-modified reduced graphene oxide/polyacrylonitrile composites

Interface control and dispersion of graphene base nanomaterials in polymer matrix are challenging to develop high comprehensive nanocomposites due to their strong interlayer cohesive energy and chemical inertia. In this research, an efficient approach is presented to functionalize reduced graphene oxide nanosheets by N-[3-(trimethoxylsilyl)propyl]ethylenediamine, which is dispersed into polyacrylonitrile to prepare N-[3-(trimethoxylsilyl)propyl]ethylenediamine – reduced graphene oxide/polyacrylonitrile nanocomposites. A thermogravimetric analysis technique was employed to evaluate thermal properties of the nanocomposites. The tribological properties of the polyacrylonitrile/graphene nanocomposites were investigated. The morphologies and volume of the worn surface were examined using a 3D profilometer. The impact of loading ratio on friction coefficient, carry-bearing capacity and durability were studied. The N-[3-(trimethoxylsilyl)propyl]ethylenediamine – reduced graphene oxide/polyacrylonitrile nanocomposite with appropriate loading ratio of reduced graphene oxide exhibited a high load-bearing capacity and durability. Therefore, the polyacrylonitrile/graphene nanocomposite shows promising potential to industrial applications involving the lubrication and anti-wear.     

Effect of tungsten addition on thermal conductivity of graphite/copper composites

Graphite/copper composites with high thermal conductivity were fabricated by tungsten addition, which formed a thin tungsten carbide layer at the interface. The microstructure and thermal conductivity of the composite material were studied. The results indicated that the insertion of tungsten carbide layer obviously suppressed spheroidization of copper coating on the graphite particles during the sintering process, and decreased the interfacial thermal resistance of the composites. Compared with the graphite/copper composites without tungsten, the thermal conductivity of the obtained composites was increased by 43.6%.     

Mechanical and microstructural behavior of nanocomposites produced via cold spray

Cold spraying is an innovative coating technology mainly based on the high speed impact of metals and ceramic particles on different substrates. Through the employment of low temperature gases (Air, He, N₂) spray particles (usually 1–50 μm in diameter) are accelerated to a high velocity (typically 300–1200 m/s) that is generated through a convergent–divergent de Laval type nozzle. Severe plastic deformation of particles impacting on the substrate occurs at temperature well below the melting point leading to the unique mechanical properties experienced by such kinds of coatings. In the present paper the main processing parameters affecting the microstructural and mechanical behavior of metal–metal cold spray deposits are described. The effect of processing parameters on grain refinement and mechanical properties were analyzed for different particles (Ti–TiAl₃, Al–Al₂O₃, Ni–Cr₃C₂, Ni–BN, Cu–Al₂O₃, Co–SiC). The results belonging to the properties of the formed nanocomposites were compared with those of the pure parent materials sprayed in the same conditions. Many experimental conditions have been analyzed in terms of particle dimensions and composition, substrate temperature and composition, gas temperature and pressure, nozzle properties. In particular, those conditions leading to a strong grain refinement with an acceptable level of the mechanical deposit properties such as porosity, adhesion strength and hardness were underlined.     

Enhanced stress transfer and thermal properties of polyimide composites with covalent functionalized reduced graphene oxide

This work prepares (3-aminopropyl) trimethoxysilane (APTMS)-functionalized reduced graphene oxide (APTMS-rGO)/polyimide (PI) composite (APTMS-rGO/PI) through in-situ polymerization. NH₂-functionalized rGO coupled by APTMS demonstrates the good reinforced efficiency in mechanical and thermal properties, which is ascribed to the covalent-functionalized PI matrix by APTMS-rGO sheets. The uniform dispersion of APTMS-rGO increases the glass transition temperature (Tg) and the thermal decomposition temperature (Td), exhibiting 21.7 °C and 44 °C improvements, respectively. The tensile strength of the composites with 0.3 wt% APTMS-rGO is 31% higher than that of neat PI, and Young’s modulus is 35% higher than that of neat PI. Raman spectroscopy show the obvious G band shift, and also clearly demonstrates the enhanced interfacial interaction between rGO nanofillers and PI matrix. The high mechanical property of the APTMS-rGO/PI composites is attributed to the covalent functionalized GO by NH₂ groups and its good dispersion in comparison with GO.     

Investigation of mechanical and tribological behaviors of multilayer graphene reinforced Ni3Al matrix composites

Multilayer graphene (MLG) shows an attractive prospect for the demanding engineering applications. This paper reports the mechanical and tribological properties of MLG reinforced Ni₃Al matrix composites (NMCs) under dry sliding at varying sliding speed. The hardness and elastic modulus of the NMCs are significantly influenced with MLG content. It is found that the hardness and elastic modulus of the NMCs are found to be increased by increasing MLG content up to 1.0 wt.%, while decreased when MLG content is above 1.0 wt.%. Tribological experiments suggest that MLG can dramatically improve the wear resistance and decrease the friction coefficient of the NMCs. Such marked improvement of wear resistance is attributed to the reinforcing mechanisms of MLG, such as crack deflection and pull-out, and reduction of friction coefficient is related to the formation of a tribofilm on the sliding contact surface.     

High performance natural rubber/thermally reduced graphite oxide nanocomposites by latex technology

The latex technology is an innovative alternative for the preparation of composites of natural rubber (NR) and thermally reduced graphite oxide (TRGO). To achieve an improvement of material properties is indispensable to prepare stable suspensions of TRGO. In this work the influence of two surfactants, such as sodium dodecyl sulfate (SDS), as ionic, and Pluronic F 127 as non-ionic surfactant, on the dispersion of TRGO in NR latex and the mechanical and physical properties of the composites were studied. The results showed that the SDS surfactant is ideal for preparing latex NR/TRGO nanocomposite. An optimum dispersion of the nanoparticles in the polymer matrix was achieved in the presence of SDS, as reflected in a considerable improvement of the physical and mechanical properties of the material. Thus, the nanocomposites with 3 phr of TRGO exhibited an improvement of nearly 400% in the maximum strength and an electrical percolation threshold with values around 10⁻⁶ S/cm, above the static limit.     

Influence of nano-alumina and sub-micron copper on mechanical properties of magnesium alloy AZ31

Magnesium composites of AZ31–Al₂O₃–Cu formulations were produced using the disintegrated melt deposition technique following by hot extrusion. Microstructural characterization showed reasonable distribution of secondary phases up to 1 vol.% of copper. A tendency to form clustered agglomeration and longer shape of secondary phases was observed when the amount of copper was increased to 1.5 vol.%. Mechanical tests indicated remarkable improvements in 0.2%YS, UTS and microhardness when nano-alumina and sub-micron copper were added into AZ31. The ductility was increased up to 9.3% in the case of AZ31–1.5Al₂O₃–1.0Cu sample and significantly reduced (5.5%) when the amount of copper was increased to 1.5 vol.%. Heat treated sample of AZ31–1.5Al₂O₃–1.0Cu showed overall improvement in both tensile strength and ductility. The results suggest that the judicious selection of composition and heat treatment has the capability to enhance overall tensile response of Mg–Al₂O₃–Cu nanocomposites.     

Improvement of mechanical properties in aluminum/CNTs nanocomposites by addition of mechanically activated graphite

Carbon nanotubes reinforced aluminum nanocomposite was prepared by ball milling route. CNTs were initially mixed with mechanically amorphized graphite. Specimens were analyzed by X-ray diffractometry and Raman spectroscopy. Crystallite size and dislocation density were calculated by modified Warren–Averbach method. Carbide formation was semi-quantitatively investigated via Raman spectroscopy. A band located in 950 cm⁻¹ was considered to be corresponded to Al₄C₃. Hardness of the samples was also evaluated using a Vickers micro-hardness tester. The hardness strengthening contributions were modeled to evaluate interfacial bonding between CNTs and the aluminum matrix. In specimens, including amorphized graphite, hardening was due to both work hardening and second phase strengthening otherwise, only due to work hardening. It was deducted that the amorphized graphite has a major role for mechanical properties improvement. This seems to be due to the formation of aluminum carbide at the interface which consequently increases adhesion of CNTs to aluminum.     

In situ preparation of reinforced polyimide nanocomposites with the noncovalently dispersed and matrix compatible MWCNTs

High performance MWCNT-reinforced polyimide nanocomposites were prepared through in situ polymerization route. 2,6-Diaminoanthraquinone (2,6-DAAQ) was selected to serve as both a diamine comonomer, and a noncovalent dispersant of MWCNTs through π–π interaction. The good dispersion of MWCNTs in both solution and polymer matrix, and high compatibility derived from the structural similarity have been proved to be particularly advantageous for the interfacial adhesion and load transfer from the polymer matrix to MWCNTs. The nanocomposites with 0.50–0.75 wt% MWCNTs had the most excellent thermal stability, thermomechanical and tensile properties, and the electrical conductivity also achieved a sharp increase at such low content. The load transfer efficiency was calculated based on both theoretical model and microscopical size measurement, and the results were rather reasonable within accepted error range.     

Surface performance and physical properties of nanoscale ceramics reinforced laser alloying composite coatings

Si₃N₄–Ni60 is firstly used to improve the wear resistance of a TA7 (Ti–5Al–2.5Sn) titanium alloy surface by mean of a laser alloying (LA) technique. The synthesis of the hard composite coating on a TA7 titanium alloy by LA of Ni60–Si₃N₄ pre-placed powders was investigated by means of scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and high resolution transmission electron microscope (HRTEM). Experimental results indicated that a number of the interdendritic lamellar eutectics, nanoscale ceramics (NC) and the amorphous phases were produced in such LA coating. The production of NC led the free energy to enhance, which increased the density of point defect, leading to the formation of hypersaturated state of point defect, causing lattice distortions. Compared with a TA7 alloy substrate, an improvement of the wear resistance was obtained for such LA composite coating.     

Thermal conductivity of Cu/diamond composites prepared by a new pretreatment of diamond powder

Cu/diamond composites were fabricated by spark plasma sintering (SPS) after the surface pretreatment of the diamond powders, in which the diamond particles were mixed with copper powder and tungsten powder (carbide forming element W). The effects of the pretreatment temperature and the diamond particle size on the thermal conductivity of diamond/copper composites were investigated. It was found that when 300 μm diamond particles and Cu–5 wt.% W were mixed and preheated at 1313 K, the composites has a relatively higher density and its thermal conductivity approaches 672 W (m K)⁻¹.     

Graphene/thermoplastic polyurethane nanocomposites: Surface modification of graphene through oxidation,polyvinyl pyrrolidone coating and reduction

Herein, oxidation, polyvinyl pyrrolidone (PVP) coating and reduction are used to modify the surface of graphene in thermoplastic polyurethane (TPU)/graphene nanocomposites. It is demonstrated that graphene could be easily dispersed in TPU with PVP absorbed on reduced graphene oxide (RGO) as stabilizer during reduction. In the stress–strain curves for these composites containing GO, PVP coated GO (GO/PVP) and reduced GO/PVP (RGO/PVP) as filler, PVP coating and reduction can largely enhance the stress in low modulus region. It is thought to largely related with enhanced interfacial interaction between filler and matrix and healing of graphene structure during reduction. Consequently, the modulus of TPU/GO/PVP and TPU/RGO/PVP is significantly increased. Meanwhile, an electrical percolation threshold of 0.35 wt.% is obtained for TPU/RGO/PVP. Comparing with the results in literature, the filler surface modification used in this study has created nanocomposites with a good balance between electrical conductivity and mechanical properties.     

Microwave assisted-in situ synthesis of porous titanium/calcium phosphate composites and their in vitro apatite-forming capability

Microwave irradiation has been proven to be an effective heating source in synthetic chemistry, and can accelerate the reaction rate, provide more uniform heating and help in developing better synthetic routes for the fabrication of bone-grafting implant materials. In this study, a new technique, which comprises microwave heating and powder metallurgy for in situ synthesis of Ti/CaP composites by using Ti powders, calcium carbonate (CaCO₃) powders and dicalcium phosphate dihydrate (CaHPO₄·2H₂O) powders, has been developed. Three different compositions of Ti:CaCO₃:CaHPO₄·2H₂O powdered mixture were employed to investigate the effect of the starting atomic ratio of the CaCO₃ to CaHPO₄·2H₂O on the phase, microstructural formation and compressive properties of the microwave synthesized composites. When the starting atomic ratio reaches 1.67, composites containing mainly alpha-titanium (α-Ti), hydroxyapatite (HA), beta-tricalcium phosphate (β-TCP) and calcium titanate (CaTiO₃) with porosity of 26%, pore size up to 152 μm, compressive strength of 212 MPa and compressive modulus of 12 GPa were formed. The in vitro apatite-forming capability of the composite was evaluated by immersing the composite into a simulated body fluid (SBF) for up to 14 days. The results showed that biodissolution occurred, followed by apatite precipitation after immersion in the SBF, suggesting that the composites are suitable for bone implant applications as apatite is an essential intermediate layer for bone cells attachment. The quantity and size of the apatite globules increased over the immersion time. After 14 days of immersion, the composite surface was fully covered by an apatite layer with a Ca/P atomic ratio approximately of 1.68, which is similar to the bone-like apatite appearing in human hard tissue. The results suggested that the microwave assisted-in situ synthesis technique can be used as an alternative to traditional powder metallurgy for the fabrication of Ti/CaP biocomposites.     

A review on basalt fibre and its composites

In recent years, both industrial and academic world are focussing their attention toward the development of sustainable composites, reinforced with natural fibres. In particular, among the natural fibres (i.e. animal, vegetable or mineral) that can be used as reinforcement, the basalt ones represent the most interesting for their properties. The aim of this review is to illustrate the results of research on this topical subject. In the introduction, mechanical, thermal and chemical properties of basalt fibre have been reviewed. Moreover, its main manufacturing technologies have been described. Then, the effect of using this mineral fibre as reinforcement of different matrices as polymer (both thermoplastic and thermoset), metal and concrete has been presented. Furthermore, an overview on the application of this fibre in biodegradable matrix composites and in hybrid composites has been provided. Finally, the studies on the industrial applications of basalt fibre reinforced composites have been reviewed.     

Mechanical properties of epoxy composites filled with silane-functionalized graphene oxide

In this work, the effects of as-produced GO and silane functionalized GO (silane-f-GO) loading and silane functionalization on the mechanical properties of epoxy composites are investigated and compared. Such silane functionalization containing epoxy ended-groups is found to effectively improve the compatibility between the silane-f-GO and the epoxy matrix. Increased storage modulus, glass transition temperature, thermal stability, tensile and flexural properties and fracture toughness of epoxy composites filled with the silane-f-GO sheets are observed compared with those of the neat epoxy and GO/epoxy composites. These findings confirm the improved dispersion and interfacial interaction in the composites arising from covalent bonds between the silane-f-GO and the epoxy matrix. Moreover, several possible fracture mechanisms, i.e. crack pinning/deflection, crack bridging, and matrix plastic deformation initiated by the debonding/delamination of GO sheets, were identified and evaluated.     

Studies on wear rate and micro-hardness of the Al/Al2O3/Gr hybrid composites produced via powder metallurgy

Micro-structural characterization of the composites has revealed fairly uniform distribution and some amount of grain refinement in the specimens. Further, it was observed that the micro-hardness improve when increasing the milling time and the reinforcement content due to presence of hard Al₂O₃ particles. Was also observed a low wear rate exhibited by the Al/Al₂O₃/Gr hybrid composites due to presence of Al₂O₃ and Gr which they acted as load bearing elements and solid lubricant respectively. The observed wear rate and micro-hardness have been correlated with microstructural analyses.     

Deformation behavior of aluminum alloy matrix composites reinforced with few-layer graphene

Microstructure and mechanical properties of aluminum alloy 2024 (Al2024)/few-layer graphene (FLG) composites produced by ball milling and hot rolling have been investigated. The presence of dispersed FLGs with high specific surface area significantly increases the strength of the composites. The composite containing 0.7 vol.% FLGs exhibits tensile strength of 700 MPa, two times higher than that of monolithic Al2024, and around 4% elongation to failure. During plastic deformation, restricted dislocation activities and the accumulated dislocation at between FLGs may contribute to strengthening of Al2024/FLG composites.     

Effects of temperature and normal load on tribological behavior of nickel-based high temperature self-lubricating wear-resistant composite coating

NiCr/Cr₃C₂–WS₂–CaF₂ mixed powders were designed and aimed to fabricate high temperature self-lubricating wear-resistant composite coating by laser cladding. The friction and wear properties of the coating were investigated under different temperatures and loads against Si₃N₄ ceramic ball. Results show that friction coefficient decreases with the increasing temperature while the wear rate firstly decreases and then increases with the increasing temperature. Both the friction coefficient and wear rate firstly decreases and then slightly increases with the increasing normal load. The coating exhibits relatively excellent tribological behavior under moderate temperature and moderate normal load.     

Fatigue properties and fracture analysis of a SiC fiber-reinforced titanium matrix composite

Tension–tension fatigue properties of SiC fiber reinforced Ti–6Al–4V matrix composite (SiC_f/Ti–6Al–4V) at room temperature were investigated. Fatigue tests were conducted under a load-controlled mode with a stress ratio 0.1 and a frequency 10 Hz under a maximum applied stress ranging from 600 to 1200 MPa. The relationship between the applied stress and fatigue life was determined and fracture surfaces were examined to study the fatigue damage and fracture failure mechanisms using SEM. The results show that, the fatigue life of the SiC_f/Ti–6Al–4V composite decreases substantially in proportion to the increase in maximum applied stress. Moreover, in the medium and high life range, the relationship between the maximum applied stress and cycles to failure in the semi-logarithmic system could be fitted as a linear equation: S_max/μ = 1.381 − 0.152 × lgN_f. Fractographic analysis revealed that fatigue fracture surfaces consist of a fatigued region and a fast fracture region. The fraction of the fatigued region with respect to the total fracture surface decreases with the increase of the applied maximum stresses.     

Influence of B4C on the tribological and mechanical properties of Al 7075–B4C composites

In the present investigation, the influence of B₄C on the mechanical and Tribological behavior of Al 7075 composites is identified. Al 7075 particle reinforced composites were produced through casting, K₂TiF₆ added as the flux, to overcome the wetting problem between B₄C and liquid aluminium metal. The aluminium B₄C composites thus produced were subsequently subjected to T6 heat treatment. The samples of Al 7075 composites were tested for hardness, tensile, compression, flexural strengths and wear behavior. The test results showed increasing hardness of composites compared with the base alloy because of the presence of the increased ceramic phase. The wear resistance of the composites increased with increasing content of B₄C particles, and the wear rate was significantly less for the composite material compared to the matrix alloy. A mechanically mixed layer containing oxygen and iron was observed on the surface, and this acted as an effective insulation layer preventing metal to metal contact. The coefficient of friction decreased with increased B₄C content and reached its minimum at 10 vol% B₄C.