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.     

Kinetic analysis on Al2O3/Cu composite prepared by mechanical activation and internal oxidation

The Al₂O₃/Cu composite was prepared by mechanical activation and internal oxidation process. Kinetic factors, which influenced the internal oxidation process, were also discussed in the present paper. The results showed that the duration of the internal oxidation was highly shortened after the powders were treated by mechanical activation. The typical internal oxidation duration was only 1 h. It is unnecessary for further prolonging internal oxidation time. Besides, in order to get a complete internal oxidation heating rate and green density of the compact are another two control factors. Their parameters should be controlled from Al contents in the powders. In this research, the optimum internal oxidation duration, heating rate and green density are 1 h, 20 °C/min and 80%, respectively, for Cu–0.8 wt% Al/Cu₂O powders. After the internal oxidation, uniform spherical -Al₂O₃ particles with an average size 0.5–0.8 μm in diameter were observed in the Cu matrix.     

Microstructure evolution and mechanical properties in ultrafine grained Al/TiC composite fabricated by accumulative roll bonding

In this study, the influence of nano-TiC particle on microstructure development and mechanical properties of Al/TiC composite fabricated by accumulative roll bonding (ARB) was considered to investigate. Microstructural characterization by electron backscatter diffraction (EBSD) system proved that the grain size decreased to around 200 nm and the TiC reinforcement particles were uniformly distributed in the Al matrix by 7-cycle of the ARB process. It is also found that presence of the TiC particles could accelerate grain refinement. Uniaxial tensile test exhibited that yield and ultimate tensile strength significantly improved more than four times in the 7-cycle ARB processed Al/TiC composite compared with the annealed aluminum specimen which used as the starting material. In addition, the obtained results demonstrated that adding the TiC reinforcement particles could improve the yield strength of the 7-cycle ARB processed Al sheet about 40 percentage.     

Fabrication of aluminum matrix composites with enhanced mechanical properties reinforced by in situ generated MgAl2O4 whiskers

Aluminum matrix composite reinforced by in situ generated single crystalline MgAl₂O₄ whiskers was fabricated by chemical synthesis method in an Al-Mg-H₃BO₃ system. A large number of MgAl₂O₄ whiskers were generated during the sintering process and distributed homogeneously in the Al matrix. The whiskers penetrate into the matrix grains to form the framework of the materials, leading to an incredible increase in mechanical properties of the composites. The generation mechanism of the MgAl₂O₄ whiskers was also discussed.     

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.     

Production of high strength Al-Al2O3 composite by accumulative roll bonding

Recently accumulative roll bonding has been used as a novel method to produce particle reinforced metal matrix composites. In this study, aluminum matrix composite reinforced by submicron particulate alumina was successfully produced and the effects of number of ARB cycles and the amount of alumina content on the microstructure and mechanical properties of composites were investigated. According to the results of tensile tests, it is shown that the yield and tensile strengths of the composite are increased with the number of ARB cycles. Scanning electron microscopy (SEM) reveals that particles have a random and uniform distribution in the matrix by the ARB cycles and a strong mechanical bonding takes place at the interface of particle-matrix. It is also found that the tensile strength of the composite, as a function of alumina content, has a maximum value at 2 vol.%, which is 5.1 times higher than that of the annealed aluminum.     

Enhanced strength and excellent transport properties of a superaligned carbon nanotubes reinforced copper matrix laminar composite

Superaligned carbon nanotube (SACNT) reinforced copper matrix laminar composites have been fabricated by means of the traditional copper sulfate electroplating process. The mechanical properties and transport properties of the Cu/SACNT composites with different SACNT content have been studied systematically, and the experimental results show that the as-prepared composites possess a better comprehensive performance than pure copper. The simple rule of mixtures (ROM) has been used to estimate the potential maximum properties of the Cu/SACNT composites. The Cu/SACNT composite is considered to be a promising material for electronics and communications applications.     

A magnesium alloy matrix composite reinforced with metallic glass

Novel light-weight materials of advanced performance are now experiencing global interest due to the strong need to reduce energy consumption in land and air transportation sectors. Here we report on a novel magnesium alloy matrix composite material. The reinforcing phase in the magnesium alloy is a fine dispersion of metallic glass particles. The composite is sintered from the powder mixture of the alloy and metallic glass at a temperature slightly above the glass transition T_g of the metallic glass particles that is close to the Mg alloy’s solidus temperature. At the compaction temperature, the metallic glass acts as a soft liquid-like binder but upon cooling it becomes the hard reinforcement component of the composite. Processing, microstructure and mechanical properties of the composite are discussed.     

Void formation in metal matrix composites by solidification and shrinkage of an AlSi7 matrix between densely packed particles

Particle reinforced metals are developed as heat sink materials for advanced thermal management applications. Metal matrix composites combine the high thermal conductivity of a metal with a low coefficient of thermal expansion of ceramic reinforcements. SiC and carbon diamond particle reinforced aluminum offer suitable thermal properties for heat sink applications. These composites are produced by liquid metal infiltration of a densely packed particle preform. Wettability, interface bonding strength and thermal mismatch are critical for void formation which leads to thermal fatigue damage under operation. The evolution of voids in AlSiC and AlCD has been studied by in-situ high resolution synchrotron tomography during matrix solidification. Large irregularly shaped matrix voids form during eutectic solidification. These voids help alleviate thermal expansion mismatch stresses by visco-plastic matrix deformation during cooling to RT after solidification, if sufficient interface bonding strength is assumed.     

Analysis of the elastic properties of an interpenetrating AlSi12-Al2O3 composite using ultrasound phase spectroscopy

An interpenetrating composite fabricated by squeeze-casting a eutectic aluminium-silicon alloy into a porous alumina preform is studied in this work. The preform was fabricated by pyrolysis of cellulose fibres used as pore forming agent, pressing of the green ceramic body and subsequent sintering of alumina particles. The resulting preform had both micropores within the ceramic walls and macropores between those walls, which were infiltrated by the liquid metal. Composites with alumina contents varied in the range of 18-65 vol.% were studied. Three longitudinal and three shear elastic constants of the composites were determined using ultrasound phase spectroscopy on rectangular parallelepiped samples. Complete stiffness matrix of one sample was determined by modifying the sample geometry by cutting at the corners of the sample and subsequent ultrasonic measurements. All composites exhibit a moderately anisotropic behavior, which can be attributed to a non-random pore orientation distribution caused by uni-axial pressing of the preforms prior to sintering. The experimental results are compared with several theoretical micromechanical models.     

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.     

Effects of carbon nanotube aspect ratio on strengthening and tribological behavior of ultra high molecular weight polyethylene composite

Carbon-based nanomaterials are great choice as reinforcement to Ultra-High Molecular-Weight Polyethylene (UHMWPE), with potential use in orthopedics. While high in-plane-stiffness and strength of these nanomaterials help in toughening, their weaker out-of-plane integrity offers lubrication. Present study investigates effect of aspect ratio of carbon nanotubes (CNT) on toughening and solid-lubrication efficiency of UHMWPE-matrix. A nominal 0.05–0.1 wt.% of CNT addition increases hardness and elastic modulus of UHMWPE by 3–45% and 8–42%, respectively. Higher aspect ratio (HAR) CNTs are found more effective in improving hardness and modulus of UHMWPE. Wear rate and friction-coefficient also increase by 530% and 220%, respectively, while reinforced with HAR CNTs. Thermal analysis shows slight increase in crystallinity and stability of composite. HAR CNTs improve interfacial bonding with matrix, due to their morphological similarity to polymer chains, as compared to low aspect ratio CNT. Aspect ratio of CNTs significantly dominates strengthening and tribological behavior of UHMWPE.     

Microstructure and chemical analysis of C/Cu/Al interfacial zones

The fibre–matrix interface in carbon–aluminium composites has been examined. Composites were prepared using uncoated carbon preforms and carbon preforms coated with copper. Auger and transmission electron microprobe microscopy were used to study the interface. The role of the copper layer on the microstructural and chemical evolution of the system after a 96 h heat treatment at 600 °C is discussed.     

On the properties and tribological behaviors of P/M iron based composites reinforced with ultrafine particulates

This paper describes the changes of structure, some mechanical and tribological properties of P/M iron based composites reinforced with ultrafine additives. Nanocrystalline additives of oxides, borides and diamond in the base material allow increasing the compressive strength and the tensile strength 1.5–3 times. An introduction of 0.2–0.3 wt% of ultrafine-grained diamonds, 0.5 wt% of chromium borides and 0.2–0.5 wt% of alumina or oxides mixture provides the best results. The coefficients of friction of MMCs containing nanocrystalline particulates are reduced 2–3 times compared to the base P/M material while the critical seizure pressure is enhanced 2–5 times. The wear resistance of the MMCs increases 2–4 times.     

Interfacial design of Cu/SiC composites prepared by powder metallurgy for heat sink applications

In order to dissipate the heat generated in electronic packages, suitable materials must be developed as heat spreaders or heat sinks. Metal matrix composites (MMCs) offer the possibility to tailor the properties of a metal (Cu) by adding an appropriate reinforcement phase (SiC) to meet the demands for high thermal conductivities in thermal management applications. Copper/SiC composites have been produced by powder metallurgy. Silicon carbide is not stable in copper at the temperature needed for the fabrication of Cu/SiC. The major challenge in development of Cu/SiC is the suppression of this reaction between copper and SiC. Improvements in bonding strength and thermo-physical properties of the composites have been achieved by a vapour deposited molybdenum coating on SiC powders to control the detrimental interfacial reactions.     

Mechanical properties of hot pressed SiCp and B4Cp/Alumix 123 composites alloyed with minor Zr

In the present study, effect of Zr addition on the microstructure and wear behavior of aluminum alloy composites (AMCs) reinforced with B4Cp and SiCp particles fabricated via hot pressing were investigated. The samples for the study composed of unreinforced aluminum alloy (Alumix 123) and the composites reinforced with 10% B4Cp and % SiCp were prepared by hot isostatic pressing (HIP) method. Similarly, all the samples alloyed with 0.2% Zr were also produced in order to make a comparison. The produced samples were evaluated for microstructural properties and mechanical tests for hardness, tensile and bending strength were performed. Wear test was carried out at 5 mm/s sliding speed under 3.0 N load for the all kind of hot pressed produced samples. The hot pressed composite microstructures have a more uniform distribution of the reinforcements. After HIP process, the composites were successfully produced with high density (>99%). The addition of Zr increased the yield and tensile strength of the samples. The highest strength value was found for the sample Al 123 matrix alloy with Zr. Evaluation of microstructures showed that copper and zirconium dispersed equally within the matrix microstructure without agglomeration. For the composite samples, Al3Zr, appeared as white precipitate, were inspected around B4C and SiC particles. The composite containing SiC particles and Zr had wear resistance value superior to those of the other counterparts.     

Forming behavior and workability of 6061/B4CP composite during hot deformation

Compression tests of 6061/B₄C_P composite have been performed in the compression temperature range from 300 °C to 500 °C and the strain rate range from 0.001 s⁻¹ to 1 s⁻¹. The flow behavior and processing map have been investigated using the corrected data to elimination of effect of friction. The processing maps exhibited two deterministic domains, one was situated at the temperature between 300 °C and 400 °C with strain rate between 0.003 s⁻¹ and 0.18 s⁻¹ and the other was situated at the temperature between 425 °C and 500 °C with strain rate between 0.003 s⁻¹ and 0.18 s⁻¹.The estimated apparent activation energies of these two domains, were 129 kJ/mol and 149 kJ/mol, which suggested that the deformation mechanisms were controlled by cross-slip and lattice self-diffusion respectively. The optimum parameters of hot working for the experimental composite were 350 °C - 0.01 s⁻¹ and 500 °C - 0.01 s⁻¹. In order to exactly predict dangerous damaging mechanism under different deformation conditions exactly, Gegel’s criterion was applied to obtain processing map in the paper. The result showed that the processing map used Gegel’s criterion can be effectively to predict the material behavior of the experimental composite.     

Mechanical and tribological properties of self-lubricating metal matrix nanocomposites reinforced by carbon nanotubes (CNTs) and graphene – A review

Rapid innovation in nanotechnology in recent years enabled development of advanced metal matrix nanocomposites for structural engineering and functional devices. Carbonous materials, such as graphite, carbon nanotubes (CNT's), and graphene possess unique electrical, mechanical, and thermal properties. Owe to their lubricious nature, these carbonous materials have attracted researchers to synthesize lightweight self-lubricating metal matrix nanocomposites with superior mechanical and tribological properties for several applications in automotive and aerospace industries. This review focuses on the recent development in mechanical and tribological behavior of self-lubricating metallic nanocomposites reinforced by carbonous nanomaterials such as CNT and graphene. The review includes development of self-lubricating nanocomposites, related issues in their processing, their characterization, and investigation of their tribological behavior. The results reveal that adding CNT and graphene to metals decreases both coefficient of friction and wear rate as well as increases the tensile strength. The mechanisms involved for the improved mechanical and tribological behavior is discussed.     

High shear dispersion technology prior to twin roll casting for high performance magnesium/SiCp metal matrix composite strip fabrication

SiC particulate (SiC_p) reinforced AZ31 magnesium alloy composite strips were produced by a novel process. In the process, a high shear technique was utilised to disperse the reinforcing particles uniformly into the matrix alloy, and AZ31/5 vol%SiC_p slurry was solidified into thin strip by a horizontal twin roll caster. The experimental results showed that the AZ31/5 vol%SiC_p strip obtained with high shear treatment exhibited a significantly refined microstructure and uniform distribution of reinforcing SiC particles. High cooling rate in the TRC process was also considered to contribute to the grain refinement of the matrix alloy, together with the possible heterogeneous nucleation effect of the reinforcing particles. The mechanical properties of the high shear treated composites strips showed enhanced modulus, yield strength and ductility by hardness and tensile tests. The experimental results were discussed in terms of the microstructural features and the macroscopic reliability, where necessary, analytical and statistical analyses were conducted.     

Infiltrated Cu8Al–Ti alumina composites

The effect of titanium additions on the interface and mechanical properties of infiltrated Cu8 wt%Al–Al₂O₃ composites containing 57 ± 2 vol% ceramic are investigated, exploring two different Al₂O₃ particle types and four different Ti concentrations (0, 0.2, 1, 2 wt%Ti). Addition of 0.2 wt%Ti leads to the development of a thin (5–10 nm) layer enriched in Ti at the interface between Cu alloy and Al₂O₃ particles; this Ti concentration produces the best mechanical properties. With higher Ti-contents Ti₃(Cu, Al)₃O appears; this decreases both the interface and composite strength. Composites reinforced with vapor-grown polygonal alumina particles show superior mechanical properties compared to those reinforced by angular comminuted alumina particles, as has been previously documented for aluminum-based matrices. Micromechanical analysis shows that damage accumulation is more extensive, as is matrix hardening by dislocation emission during composite cooldown, in the present Cu8 wt%Al matrix composites compared with similarly reinforced and processed Al-matrix composites.