In this research, the micro-milling process using nano-solid dry lubrication is studied for machining multidirectional carbon fiber reinforced plastic (MD-CFRP). For the nano-solid dry lubrication, two kinds of graphene nanoplatelets and multiwall carbon nanotubes are used as nanoparticles. The workpiece is an MD-CFRP composite in which 10 plies of prepreg are laminated and it consists of four carbon fiber orientations — 0°, 45°, 90°, 135°. After a series of micro-milling experiments, the workpiece surface quality and tool wear are investigated. Overall, it is found that the nano-solid dry lubrication can improve the surface quality and reduce the tool wear. In particular, larger graphene nanoplatelets (xGnP H-5) are more advantageous than smaller graphene nanoplatelets (xGnP C-750). In addition, multiwall carbon nanotubes having a tube-shape structure are less effective than graphene nanoplatelets having a two-dimensional thin sheet shape for enhancing the micro-milling performances, which may be due to better lubrication effect with the graphene nanoplatelets’ sliding phenomenon at the cutting region.

Titanium is widely used in many industry areas (such as automotive industry, aerospace industry, and medical industry) due to its superior properties of low density, high strength to weight ratio, strong corrosion-resistance, etc. However, commercial pure titanium (CP-Ti) parts still have some disadvantages (such as relatively low hardness, and wear resistance) which limit their further applications. In order to reduce these disadvantages, some reinforcement materials (such as ceramics and nanomaterials) are involved to fabricate titanium-based parts Compared with ceramics, low content of nanomaterials could significantly improve the mechanical properties and reduce disadvantages of ceramics (such as poor wettability and low interfacial bonding between reinforcement materials and Ti). Graphene oxide (GO) is a preferable candidate of nanomaterial due to its excellent mechanical properties and low density. The GO reinforced Ti parts have been fabricated by the selective laser sintering (SLS) process. Laser additive manufacturing (LAM) process includes directed energy deposition method and powder bed fusion method. Compared with powder bed fusion method (such as the SLS and selective laser melting (SLM)), directed energy deposition method (e.g. laser engineered net shaping (LENS)) has advantages of parts repairing and gradient parts fabrication capabilities. There are no studies on the fabrication of GO-Ti parts by LENS process. In this study, GO-Ti parts are fabricated by the LENS process. The effects of GO and laser power on fabricating defects of porosity, microstructure, and mechanical properties (including microhardness, elastic modulus, wear rate) were studied, for the first time.

Owing to its high stiffness and strength, low density, and excellent flexibility, nano-sized graphene oxide (GO) is considered as a competitive material to reinforce metallic materials. Conventional manufacturing methods for GO reinforced metal matrix fabrication include casting and powder metallurgy, both of which demonstrate disadvantages of high reinforcement agglomeration, high cost, and difficulty in fabrication of complex structures. To reduce these problems, it is important to investigate a finely-controlled, cost-saving, and near-net-shaping process for GO reinforced metal matrix manufacturing. Laser additive manufacturing is such a process that mainly includes selective laser sintering / melting (SLS / M) and laser deposition-additive manufacturing (LD-AM). Compared with SLS / M, LD-AM demonstrates parts remanufacturing capability and is capable of fabricating functionally gradient materials. In this investigation, GO reinforced Inconel 718 (IN718) parts, for the first time, are fabricated using LD-AM processes. The effects of GO on flatness, surface roughness, microstructure, microhardness, and wear resistance of LD-AM fabricated GO reinforced IN718 parts are studied. Experimental results show that the introduction of GO is beneficial for enhancing both microhardness and wear resistance but harmful to surface quality of fabricated parts. In addition, the presence of GO has little influence on microstructures.

Graphene synthesis on ultra-thin catalysts can allow the use of graphene-coated metal films in electronic applications. Graphene coated thin films are expected to offer superior mechanical performance owing to the strength of graphene. However, several factors need to be considered to assure the stability of thin films at the high temperatures required for graphene synthesis. In this work, we present a systematic framework for the selection of thin films (< 1 micron thickness) to be used as catalyst for graphene synthesis. We present our progress towards the rapid synthesis of graphene at 1100°C in less than two minutes, thus avoiding solid state dewetting. The quality of the graphene is assessed by Scanning Electron Microscopy, Raman spectroscopy and indentation. It is shown that these films exhibit higher stiffness and resistance to crack propagation.

The effect of graphene nanoplatelets (GNPs) on enhancing the interlaminar fracture toughness of glass fiber/epoxy composites was investigated. The GnPs were physically deposited on the fiber surface by the dip coating technique. The composites were fabricated by hand layup technique followed by the compression molding process. Mode-I fracture test was conducted on the composite specimens. Crack propagation was studied by the digital image correlation (DIC) technique. Mode-I fracture toughness for composites loaded with 0.5 wt.% GnPs showed improvement by an average of 60% when compared to the pristine composites. It is concluded that the addition of GnPs produces a strong fiber/matrix interface bonding which effectively limits the crack propagation.

Graphene is an ideal reinforcement material for metal matrix composites (MMC) owing to its high strength, high ductility, light weight, as well as good bonding with metal matrix. Additive manufacturing such as selective laser melting (SLM) brings the advantages of low material waste, high flexibility, and short production lead cycle. In this study, graphene nano-platelets (GNPs) reinforced Inconel 718 composites are fabricated by SLM technique and processed under various post heat treatment schemes. It is found that fabrication of GNPs reinforced MMC using SLM technique is a viable approach. The obtained composite possesses dense microstructure and enhanced tensile strength. Post heat treatments at two levels of solution temperature (980 and 1220°C) for 1 hour followed by two-step aging are carried out. The experiment results indicate that addition of GNPs into Inconel 718 matrix results in significant strength improvement. At as-built condition, the ultimate tensile strengths are 997 and 1447 MPa, respectively at 0 and 4.4vol.% GNP content. Moreover, under as-built and solution treated condition, high content of GNPs results in overall higher UTS value and the strengthening effect is most significant at as-built condition. Meanwhile, γ′ and γ″ precipitation hardening is suppressed in the GNPs reinforced composite under aged condition due to the formation of MC carbide and depletion of Nb. Incorporating GNPs in Inconel 718 effectively inhibits the grain growth during post heat treatment.

3D printing (additive manufacturing) has become a popular method to create three-dimensional objects due to its high efficiency and is easy to operate. 3D printing of continuous fiber reinforced polymers has been a challenge. The fused deposition modeling (FDM) processes for this purpose were proposed and made possible only several years ago. The 3D printed continuous fiber reinforced polymers are able to improve the mechanical properties by leaps and bounds. In this paper, we aim to investigate the possibility of further improve the mechanical properties of 3D printed continuous fiber reinforced polymers by adding nano fillers to the polymer matrix. In experiment, the Kevlar fiber is chosen to be the continuous fiber material, and nylon 6 (PA 6) is chosen to be the polymer matrix material. Carbon nanotubes (CNTs) and graphene nano platelets (GNPs) nanoparticles are first mixed with nylon 6 pellets to make nanocomposites. The nanocomposites are then extruded into filaments for 3D printing. During the 3D printing process, both Kevlar filament and nanocomposite filament are fed through the printing nozzle and deposited on the platform. Tensile specimens are made from pure PA 6 and four types of nanocomposites, namely, 0.1wt% CNT/PA 6, 1wt% CNT/PA 6, 0.1wt% GNP/PA 6, 1wt% GNP/PA 6. By incorporating four layers of Kevlar fiber, which leads to the weight percentage of about 9% for Kevlar fiber in materials, fiber composite tensile specimens are made from Kevlar/PA 6 composite and four fiber reinforced nanocomposites, namely, Kevlar/0.1%CNT/PA 6, Kevlar/1%CNT/PA 6, Kevlar/0.1%GNP/PA 6, and Kevlar/1%GNP/PA 6. The tensile tests reveal that CNTs filled PA 6 nanocomposites show less significant improvements in mechanical properties as compared to the GNP filled PA 6. With only 0.1wt% of GNP, the tensile modulus improves by 101%, and with 1wt% of GNP, the modulus improves by 153%. The results also indicate that although Kevlar fibers dominate the main mechanical properties of the printed composite materials, the existence of GNP nano fillers also provide noticeable contribution to the enhancement of tensile strengths and moduli, while the effect of CNTs is much less pronounced.

Flexible tactile sensors have been utilized for epidermal pressure sensing, motion detecting, and healthcare monitoring in robotic and biomedical applications. This paper develops a novel piezoresistive flexible tactile sensor based on porous graphene sponges. The structural design, working principle, and fabrication method of the tactile sensor are presented. The developed tactile sensor has 3 × 3 sensing units and has a spatial resolution of 3.5 mm. Then, experimental setup and characterization of this tactile sensor are conducted. Results indicated that the developed flexible tactile sensor has good linearity and features two sensitivities of 2.08 V/N and 0.68 V/N. The high sensitivity can be used for tiny force detection. Human body wearing experiments demonstrated that this sensor can be used for distributed force sensing when the hand stretches and clenches. Thus the developed tactile sensor may have great potential in the applications of intelligent robotics and healthcare monitoring.

This paper investigates a new technology to create functionally graded material (FGM) by additive manufacturing (AM). In particular, this paper focuses on creating graphene-polymer composite FGM by laser-based sintering processes. Graphene-polymer composites have received high attention in AM due to their excellent electrical conductivity, thermal stability and mechanical strength. However, AM of the graphene-polymer composites has a huge challenge to overcome. The heterogeneous materials should be mixed properly, and it is not easy to achieve the desired composite characteristics solely by changing the mass ratio of graphene. This paper shows a newly developed laser-assisted AM system for the graphene-polymer composite FGM by laser-based sintering processes. The paper also describes two methods of material integration: mixing graphene and polyethylene powders before sintering, and depositing the different material powders separately and sintering them. This study identified that the two methods led to different mechanical and electrical properties of the created parts. Thus this paper demonstrates the possibility to create quite useful hybrid (mechanically and electrically) FGM composites.

This paper presents graphene growth on Pt deposited on four different adhesion layers such as Ti, Cr, Ta, and Ni. During the graphene growth at 1000 °C using conventional Chemical Vapor Deposition method, these adhesion layers diffuse into and alloy with Pt layer resulting graphene to grow on different alloys. Therefore, Pt layer on different adhesion layers induces different quality and number of layer(s) of graphene grown on the film. Monolayer graphene was produced on majority of metal layers except on Pt/Ta layer where bilayer graphene is observed. The lowest defects were found on graphene grown on Pt/Ni film where slightly higher number of wrinkles are observed compared to other alloys. We characterized graphene using SEM images of transferred graphene, of Pt grains after the growth of graphene, and of in-depth profiles of thin film via TOF-SIMS. Our paper states feasibility of graphene growth on Pt thin film on various adhesion layers and obstacles to overcome to enhance graphene transfer from Pt thin film. We address one of the major difficulties of graphene growth and transfer to implement graphene in NEMS/MEMS devices.

Graphene nanoplatelets (GNPs) have many outstanding properties, such as high mechanical strengths, light weight, and high electric conductivity. These unique properties make it an ideal reinforcement used for metal matrix composite (MMCs). In the past few years, many studies have been performed to incorporate GNPs into metal matrix and investigate the properties of obtained metal matrix composites. Meanwhile, fabrication of MMCs through laser assisted additive manufacturing (LAAM) has attracted much attention in recent years due to the advantages of low waste, high precision, short production lead time, and high workpiece complexity capability. In this study, the two attractive features are combined to produce GNPs reinforced MMC using selective laser melting (SLM) process, one of the LAAM processes. The target metal matrix material is Inconel 718, a nickel-based Ni-Cr-Fe austenitic superalloy that possesses excellent workability and mechanical performance and has wide applications in industries. Inconel 718 holds outstanding mechanical performance, corrosion, oxidation, and wear performance over a wide range of temperatures, making it an attractive superalloy used for high temperature service components. In the experiment, pure Inconel 718 and GNPs reinforced Inconel 718 composites with two levels of GNPs content (i.e., 0.25 and 1 wt.%) are obtained by SLM. Note that the SLM process, a novel powder mixture procedure is adopted to ensure the even dispersion of GNPs in the Inconel 718 powders. Room temperature tensile tests are conducted to evaluate the tensile properties. Scanning electron microscopy (SEM) observations are conducted to analyze the fracture surface of materials and to understand the reinforcing mechanism. It is found that fabrication of GNPs reinforced MMC using SLM is a viable approach. The obtained composite possesses dense microstructure and significantly enhanced tensile strength. The ultimate tensile strengths (UTS) are 997.8, 1296.3 and 1511.6 MPa, and the Young’s moduli are 475, 536, and 675 GPa, for 0 wt.% (pure Inconel 718), 0.25 wt.%, and 1 wt.% GNP additions, respectively. The bonding between GNPs and matrix material appears to be strong, and GNPs are well retained during the SLM process. The strengthening effect and mechanisms involved in the composites are discussed. Load transfer, thermal expansion coefficient mismatch, and dislocation hindering are believed to be the three main reinforcing mechanisms involved. It should be noted that more work needs to be conducted in the future to obtain more comprehensive information regarding other static and dynamic properties, and the high temperature performances of the GNP reinforced MMCs produced by SLM. Process parameter optimization should also be investigated.

This paper presented a novel 3D printing technique to fabricate graphene aerogel based on directional freezing. Thermal property of the graphene ink is one of key factors in this process which affects the material integrity and morphology as well as process efficiency and reliability. The major objective of this paper is to develop a heat transfer model to efficiently and reliably predict the temperature evolution of the printed materials and the waiting time between the layers for any input geometry. The simulation results show that the input geometry significantly affects the temperature evolution and waiting time. The proposed technique can not only improve the process efficiency and reliability, it can also serve as a flexible tool to predict and control the microstructure of the printed graphene aerogels.

Graphene is one of the most promising carbon nanomaterial due to its excellent electrical, thermal, optical and mechanical properties. However, it is still very challenging to unlock its exotic properties and widely adopt it in real-world applications. In this paper, we introduces a new 3D graphene structure printing approach with pure graphene oxide material, better inter-layer bonding, and complex architecture printing capability. Various parameters related to this novel process are discussed in detail in order to improve the printability, reliability and accuracy. We have shown that the print quality largely depends on the duty cycle of print head, applied pressure and travel velocity during printing. A palette of printed samples are presented to demonstrate the effectiveness of the proposed technique along with the optimal parameter settings. The proposed process proves to be a promising 3D printing technique for fabricating multi-scale nanomaterial structures. The theory revealed and parameters investigated herein are expected to significantly advance the knowledge and understanding of the fundamental mechanism of the proposed directional freezing based 3D nano printing process. Furthermore the outcome of this research has the potential to open up a new avenue for fabricating multi-functional nanomaterial objects.

One of the major challenges in producing highly accurate graphene-based nanoelectromechanical (NEMS) resonators is the poor fabrication repeatability of graphene-based NEMS devices due to small variations in the residual stress and initial tension of the graphene film. This has meant that graphene-based nanoelectromechanical resonators tend to have large variations in natural frequency and quality factor from device to device. This poor repeatability makes it impossible to use these resonators to make accurate, high-precision force and displacement sensors or electromechanical filters. However, by actively controlling the tension on the graphene resonator it is possible both to increase repeatability between devices and to increase the force/mass sensitivity of the nanoelectromechanical resonators produced. Such tension control makes it possible to produce electrometrical filters that can be precisely tuned over a frequency range of up to several orders-of-magnitude. In order to controllably strain the graphene resonator, a microelectromechanical system (MEMS) is be used to apply tension to the graphene. The MEMS device consists of a graphene resonator connected between a set of gold electrodes. Each gold electrode is located on a different MEMS stage. Each stage is connected to a set of flexural bearings which are used to guide the motion of the stage. The displacement stage is actuated using a thermal actuator that allows a uniform and constant tension to be applied to the graphene resonator. The displacement of the actuator and the tension applied to the graphene are measured using a pair of differential capacitive actuators. The resonator is actuated electrostatically using the electrical back gate, and the resonant frequency is measured from the change in conductance of the graphene as it approaches resonance. Using this setup, it is possible to tune the natural frequency of the graphene resonator with high precision and accuracy. In addition to designing devices that can compensate for manufacturing errors in nanomanufactured devices, this paper will present several methods that can greatly expand the scope and rate at which nanomaterials-based devices can be fabricated. For example, this paper will present a transfer-free, wafer-scale manufacturing process that can be used to produce suspended graphene-based devices such as the graphene-based NEMS resonators. This new method involves the growth of graphene directly on the device wafer and release of the graphene-based device through etching of the copper catalyst layer. This method replaces traditional graphene fabrication methods, such as mechanical exfoliation, electron beam lithography, or transfer from copper foils, which are slow and require a transfer step that is the source of much of inconsistency in suspended graphene-based devices. Therefore, these new transfer-free, wafer-scale fabrication methods offer the potential to increase the throughput, yield, and repeatability of manufacturing processes for graphene resonators while reducing manufacturing costs and complexity.

Graphene reinforced titanium (Ti-Gr) nanocomposites have been prepared on AISI 4140 base plate by laser sintering process. The dispersion and survival of graphene in the Ti matrix after laser treatment were discussed. Through laser sintering, graphene sheets were dispersed uniformly into Ti matrix to form Ti-Gr nanocomposites. Microstructures and components of the nanocomposites were studied using scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS) and Raman spectroscopy. It was proved by SEM images, XRD patterns and Raman spectrum that graphene survived in Ti-Gr nanocomposites after laser sintering. Hardness measurements showed the laser sintered Ti-Gr nanocomposites got more than 2-fold higher in Vickers Hardness value than that of laser sintered Ti.

This paper is aimed at investigating the effects of graphene oxide platelet (GOP) geometry (i.e., lateral size and thickness) and oxygen functionalization on the cooling and lubrication performance of GOP colloidal suspensions. The techniques of thermal reduction and ultrasonic exfoliation were used to manufacture three different types of GOPs. For each of these three types of GOPs, colloidal solutions with GOP concentrations varying between 0.1–1 wt% were evaluated for their dynamic viscosity, thermal conductivity and micromachining performance. The ultrasonically-exfoliated GOPs (with 2–3 graphene layers and lowest in-solution characteristic lateral length of 120 nm) appear to be the most favorable for micromachining applications. Even at the lowest concentration of 0.1 wt%, they are capable of providing a 51% reduction in the cutting temperature and a 25% reduction in the surface roughness value over that of the baseline semi-synthetic cutting fluid. For the thermally-reduced GOPs (with 4–8 graphene layers and in-solution characteristic lateral length of 562–2780 nm), a concentration of 0.2 wt% appears to be optimal. The findings suggest that the differences seen between the colloidal suspensions in terms of their droplet spreading, evaporation and the subsequent GOP film-formation characteristics may be better indicators of their machining performance, as opposed to their bulk fluid properties.

Part-2 of this paper is focused on studying the droplet spreading and the subsequent evaporation/film-formation characteristics of the graphene oxide colloidal solutions that were benchmarked in Part-1. A high-speed imaging investigation was conducted to study the impingement dynamics of the colloidal solutions on a heated substrate. The spreading and evaporation characteristics of the fluids were then correlated with the corresponding temperature profiles and the subsequent formation of the residual graphene oxide film on the substrate. The findings reveal that the most important criterion dictating the machining performance of these colloidal solutions is the ability to form uniform, sub-micron thick films of graphene oxide upon evaporation of the carrier fluid. Colloidal suspensions of ultrasonically-exfoliated graphene oxide at concentrations < 0.5 wt% are best suited for micromachining applications since they are seen to produce such films. The use of thermally-reduced graphene oxide suspensions at concentrations < 0.5 wt% results in non-uniform films with thickness variations in the 0–5 μm range that are responsible for the fluctuations seen in the cutting force and temperatures. At concentrations ≥ 0.5 wt%, both the thermally-reduced and ultrasonically-exfoliated graphene oxide solutions result in thicker and non-uniform films that are detrimental for machining results. The findings of this study reveal that the characterization of the residual graphene oxide film left behind on a heated substrate may be an efficient technique to evaluate different graphene oxide colloidal solutions for cutting fluids applications in micromachining.

We study the effects of wedge bluntness in mechanically exfoliating graphene layers from highly ordered pyrolytic graphite (HOPG), a layered material. Molecular dynamics simulations show that the layer initiation modes strongly depend on the wedge radius. Force and specific energy signatures are also markedly affected by the radius. Cleaving with a larger wedge radius causes buckling ahead of the wedge; larger the radius more the buckling. A critical depth of insertion of 1.6 A° is seen necessary to cleave a single layer; this is also found to be independent of wedge radius. Hence, with accurate positioning on an atomically flat HOPG surface it is possible to mechanically cleave, using a wedge, a single sheet of graphene even with a blunt wedge.

The objective of this research is to examine the micro-machining responses of a hierarchical three-phase composite made up of micro-scale glass fibers that are held together by an epoxy matrix laden with nano-scale graphene platelets. To this end, micro-milling experiments are performed on both the hierarchical graphene composite as well as on a baseline two-phase glass fiber composite without the graphene additive. The composite microstructure is characterized using transmission electron microscopy and scanning electron microscopy methods. Tool wear, chip morphology, cutting force, surface roughness and delamination are employed as machinability measures. In general, the tool wear, cutting forces, surface roughness and extent of delamination are all seen to be lower for the hierarchical graphene composite. These improvements are attributed to the fact that graphene platelets improve the thermal conductivity of the matrix, provide lubrication at the tool-chip interface and also improve the interface strength between the glass fibers and the matrix. Thus, the addition of graphene to a conventional two-phase glass fiber epoxy composite is seen to not only improve its mechanical properties but also its machinability.

Graphene is a promising material as a reinforcing element for high-strength, lightweight metal composites due to its extraordinary mechanical properties and low density. In this study, Al6061–graphene composite was investigated with 1.0 wt.% graphene reinforcement. The graphene was manufactured by the modified Brodie’s method. The Al6061 powder and graphene flakes were ball milled at different milling times (10, 30, 60, and 90 min). The composite was then synthesized by hot compaction in the semi-solid regime of the Al6061. Three point bending test was performed to characterize the mechanical properties of the composites. The ball milled powder and the fracture surfaces of the composites were investigated using the scanning electron microscopy (SEM). The results were compared with a reference Al6061 without any graphene reinforcement. For the Al6061-1.0 wt.% graphene composites, a maximum enhancement of 47% in the flexural strength was observed when compared with the reference Al6061 processed at the same condition.