Addition Of Multilayer Graphene Research Articles

Effects of thermal aging on damage evolution behavior of glass fiber reinforced composites with multilayer graphene by acoustic emission

AbstractThe thermal aging behavior of glass fiber reinforced composites has attracted much attention because of its application in elevated temperatures environments. In this study, to improve the thermal aging resistance performance of composites, multilayer graphene was embedded in glass fiber reinforced composites and the damage evolution behaviors of the composites after thermal aging treatments were investigated. The mapping relationship between damage modes and acoustic emission parameters is established by principal component analysis and k‐means clustering methods, then the acoustic emission data were trained by K‐Nearest Neighbor algorithms to obtain a damage modes identification model with positive predictive values above 90%. The results showed that more matrix cracking signals are captured (or matrix cracking accumulation acoustic emission (AE) energy is abruptly raised) at the early stage of loading after 32 days of thermal aging. With the addition of multilayer graphene, the fiber/matrix debonding accumulation AE energy is significantly less than the matrix cracking accumulation AE energy, which is more obvious after thermal aging. Damage initiation and extension obtained by the acoustic emission events help to find the correlation between aging time and interior interface damage mechanism.

Effects of graphene on thermal properties and thermal stability of polycarbonate/graphene nanocomposite

Polycarbonate (PC) /graphene nanocomposite was prepared using multilayer graphene (MLG) with loadings of 0.5, 1, and 3 wt% via melt mixing process. Morphological, structural, and thermal properties of the PC/MLG nanocomposites are investigated to look into the influence of MLG on the nanocomposite. A significant increase (∼6.4°C) in glass transition temperature is observed upon the addition of 3 wt% of MLG into the polycarbonate matrix. This increase in glass transition temperature may be due to the interaction between the MLG and polycarbonate polymer matrix. The specific heat capacity of pure PC and PC/MLG nanocomposites varies linearly with temperature below their glass transition. Upon the addition of MLGs, the overall thermal stability of PC/MLG nanocomposites increases with MLG loadings. A maximum increase about 29.23°C in Tonset of thermal decomposition is observed in PC/MLG nanocomposite having 3 wt% of MLG loading. The activation energy ( Ea) of thermal decomposition is also calculated by kinetic analysis of thermal decomposition of the PC/MLG nanocomposites using Horowitz–Metzger and Broido’s methods.

Fretting tribological behaviors of steel wires under lubricating grease with compound additives of graphene and graphite

Fretting damage among steel wires is an important cause for the fatigue fracture of wire rope. In this paper, firstly, the effect of carbon-based additives with different concentrations on the tribological performances of the special grease IRIS-200BB for wire rope was explored through a series of four-ball friction tests. Secondly, the fretting tribological behaviors of steel wires with helical structure under different lubrication conditions were studied by a self-made test rig. Results show that the anti-wear ability of the base grease is enhanced by the addition of multilayer graphene or micron graphite. In addition, micro-cutting on worn surface is obviously reduced when micron graphite and multilayer graphene are added into the base grease. For the convex friction form, the friction reduction and anti-wear performances of the base grease are effectively ameliorated by various additives, while for the concave friction form, tribological characteristics of the compound greases are inferior to that of the base grease.

Toughening of silicon nitride ceramics by addition of multilayer graphene

Silicon nitride (Si3N4) ceramics have superior mechanical properties allowing their broad application in many technical fields. In this work, Si3N4-based composites with 1–5 wt% multilayer graphene (MLG) content were fabricated by spark plasma sintering at different temperatures and holding time in order to improve the fracture resistance of the Si3N4 ceramic. Our investigation focused on understanding the relationships between the microstructure and mechanical properties with special attention to the intergranular phases between Si3N4 matrix and MLG reinforcement.We have found that nanopores developed at the Si3N4-MLG interface due to a reaction between carbon and the oxygen available in the topmost layer of the Si3N4 particles. Interface porosity has an optimum for the toughening effect. In 1 wt% MLG/Si3N4 composites nanopores are local, but separated at the Si3N4-MLG interface, which promote the MLG pull-out mechanism imparting a significant toughening effect on the composite. Beyond the optimal 1 wt% MLG content, MLG platelets agglomerate and excessive porosity are developed at the Si3N4-MLG interfaces, leading to weaker matrix- graphene adhesion and thus lower fracture toughness.

Reaction mechanism of Al-CuO nanothermites with addition of multilayer graphene

Reactions of nanothermites is complex, and the heterogeneous reaction poorly understood. In this study Al-CuO-multilayer graphene (MLG) composites were studied to explore the effects of MLG on the reaction properties, products composition and reaction mechanism of Al-CuO nanothermites. The morphology composition of Al-CuO-MLG composites before and after reaction was studied by scanning electron microscope (SEM). And detailed reaction pathways were characterized by X-ray diffraction (XRD), thermal gravimetric analysis and differential scanning calorimeter (TG-DSC) and X-ray photoelectron spectroscopy (XPS). Results indicate that the presence of MLG between nano-Al and nano-CuO particles tunes and improves reaction characteristics. A total heat of reaction of the Al-CuO-MLG (1 wt%) composites is 1679 J/g, increased by ∼87.5 J/g compared to that of Al-CuO composites.

Modification of Tribolayers of a Titanium Alloy Sliding against a Steel

The nonprotective tribolayers of the titanium alloy were modified into additives-containing tribolayers through an artificial addition of multilayer graphene (MLG), Fe2O3 nanomaterials, or their mixtures with various proportions on the titanium alloy/steel sliding interface. The sustainability of the modified tribolayers under a high load was evaluated by the critical sliding distance for a mild-to-severe wear transition. The modified tribolayers were found to significantly improve or deteriorate tribological performance of the titanium alloy, which was decided by their ingredients. The pure MLG- or Fe2O3-containing tribolayers, because of their lacking load-bearing or lubricant capacity, presented poor sustainability and readily lost protection to cause high wear loss or frictional coefficient. However, for the addition of various mixtures of MLG and Fe2O3, the modified tribolayers possessed a double-layer structure consisting of friction-reducing MLG- and wear-resistant Fe2O3-predominated layers. They presented a sustainable protection, thus remarkably improving the tribological performance of the titanium alloy.

Modification of microstructure and properties of Ti-47Al-2Cr-4Nb-0.3W alloys fabricated by SPS with trace multilayer graphene addition

In this paper, Ti-47Al-2Cr-4Nb-0.3W alloys with trace multilayer graphene addition were fabricated by spark plasma sintering to enhance both mechanical properties and tribological property simultaneously. With the addition of multilayer graphene, bending strength, compressive strength and tribological property of TiAl alloys are all improved. When graphene content increases from zero to 0.8 at.%, the mean grain size decreases from 14.8 ± 1.4 μm to 8.2 ± 0.8 μm. The bending strength reaches almost 1000 MPa and the fracture strength increases to 2347 ± 12 MPa, an increase of 15% compared with TiAl alloy. The friction coefficient also decreases from about 0.6 to 0.4, a decrease by 1/3 compared with TiAl alloy. The reasons for the improved mechanical properties and tribological property are the in-situ reaction plate-shape Ti2AlC phase, fine needle-like Ti3AlC phase as well as fine and homogeneous microstructure. The wear mechanism changes from abrasive wear to abrasive wear plus adhesive wear with the increased graphene content.

Reinforcing effect of graphene on the mechanical properties of Al2O3/TiC ceramics

Multilayer graphene (MLG)-reinforced Al2O3/TiC ceramics were fabricated through hot pressing sintering, and the reinforcing effect of MLG on the microstructure and mechanical properties of the composites was investigated by experiment and simulation. The simulation of dynamic crack initiation and propagation was investigated based on the cohesive zone method. The results show that the composite added with 0.2wt% MLG has excellent flexural strength and high fracture toughness. The major reinforcing mechanisms are the synergistic effect by strong and weak bonding interfaces, MLG pull-out, and grain refinement resulting from the addition of MLG. In addition, the aggravating of crack deflection, branching, blunting, and bridging have indispensable contribution to the improvement of the as-designed materials.

The role of multilayer graphene in the improved electrical and optical characteristics of a P3HT-based photovoltaic device

In the present work, we have studied in detail the effect of the incorporation of multilayer graphene (MLG) on the electrical and optical properties of P3HT (poly (3-hexylthiophene))-based photovoltaic (PV) devices. The PV devices were fabricated with a P3HT:MLG composite and significant improvement in the performance was observed in terms of enhanced short circuit current density (Jsc) and open circuit voltage (Voc) at the optimized MLG concentration of 0.1 wt%. The dark I–V measurements exhibit a remarkable reduction in the total series resistance (Rs) of about 63% in our typical device which is attributed to the increase in the mobility of charge carriers in the P3HT:MLG (0.1 wt%) composite film. A prominent quenching in the photoluminescence (PL) of P3HT on the addition of MLG indicates efficient electron extraction from P3HT and therefore, the increase in the Jsc is the combined effect of both the efficient charge transfer and reduction in the Rs of the device. Further, cyclic voltammetry (CV) measurements reveal that on adding MLG, there is a downshift of the highest occupied molecular orbital energy level of P3HT which in turn increases the Voc of the device by ~0.28 V.

Enhanced properties of cement mortars with multilayer graphene nanoparticles

The present work aims to combine multilayer graphene (MLG) nanoparticles with Ordinary Portland Cement (OPC) mortar specimens, evaluating possible improvements on their mechanical properties and ultimately coming up with an ideal and effective concentration for future applications. Mortars with water/cement ratio of 0.4, MLG dosage varying from 0.015 to 0.033% by weight of cement and sand at a proportion of 3× the weight of cement were prepared. 50×100mm cylindrical specimens were shaped and subjected to compressive and splitting tensile strength tests at the ages of 3, 7 and 28days. In addition, SEM micrographs and metallographic images were collected and analyzed in order to better characterize the sample’s morphology and also in attempt of explaining the MLG influence on cement paste. The optimal tensile strength was achieved with samples designed with MLG dosage of 0.033%, for which the corresponding increases were 100.0, 144.4 and 131.6%, after 3, 7 and 28days, respectively, compared with samples without MLG. On the other hand, the optimal compressive strength increases were obtained with samples designed with MLG dosage of 0.021%, with improvements of 63.6, 94.1 and 95.7% after 3, 7 and 28days, respectively, compared with samples without MLG. The addition of MLG is believed to accelerate cement hydration reactions, reduce the pore volume and harden cement properties. An improvement in thermal conductivity is also associated to MLG incorporation, and this favorable heat transfer in OPC-based mortars probably promoted the observed changes in the composite chemical structure and mechanical properties herein analyzed.

Investigation of Tribological Behaviors of TiAl-Multilayer Graphene-Microsphere Composites at Different Applied Loads

Tribological behaviors of TiAl-multilayer graphene-microsphere composites (TMMC) are investigated at different loads in this paper. The tribological results show that TMMC exhibit excellent wear and friction performances from 4 to 20 N for the formation of the intact and smooth tribo-films containing multilayer graphene (MLG) and WS2-SiO2 microsphere (WSM) on the worn surfaces. During the sliding process, MLG and WSM are ground out of TMMC to form the tribo-films on the worn surfaces, which is beneficial to the decreasing in friction coefficients and wear rates. MLG is easy to be sheared for the weak interlayer binding force, which can reduce the friction coefficients and wear rates. WSM can repair the tribo-film by filling its worn pits, resulting in the smooth worn surface and excellent tribological performance of TMMC. Moreover, the hardness of TMMC is increased for the addition of MLG and WSM, which makes contributions to the improvement of tribological behaviors of TMMC.

Improvement of tribological performance of TC11 alloy via formation of a double-layer tribo-layer containing graphene/Fe2O3 nanocomposite

Sliding friction and wear tests were performed for TC11 titanium alloy against AISI 52100 steel at room temperature and a low speed, with an addition of multilayer graphene (MLG)/Fe2O3 nanocomposites onto the sliding interface. A thin, stable double-layer tribo-layer composed of MLG-predominated and Fe2O3-predominated layers was inductively formed on the worn surface. It exerted a protective function for TC11 alloy to significantly reduce the friction and wear, which was attributed to the synergistic effect of lubricant MLG and load-bearing Fe2O3. As a comparison, however, the single-component tribo-layers were noticed to readily lose stability without protection and even accelerated friction or wear. The poor tribological performance of the titanium alloy was because tribo-layers lacks the load-bearing or lubricant capacity.

Multi-layer graphene/copper composites: Preparation using high-ratio differential speed rolling, microstructure and mechanical properties

The possibility of using multi-layer graphene (MLG) particles as reinforcement for enhancing the mechanical properties of Cu matrix composites was explored. The combination of ball milling and high-ratio differential speed rolling (HRDSR) techniques was utilized to fabricate the 0.5 and 1vol.% MLG/Cu composites. In the HRDSR-processed composites, the nanosized MLG particles with 5–15nm in diameter were dispersed densely and uniformly in the grain interiors of Cu matrix with a preferred crystallographic relationship of 〈111〉Cu//〈0001〉MLG to the matrix. The conventionally rolled composites with the same contents of MLG, however, contained much lower densities of nanosized MLG particles. This result indicates that the large shear strain induced during HRDSR accelerated breaking up of MLGs into nanosizes and enhanced their dispersion in the matrix. The strength improvement through the addition of MLGs was obvious when HRDSR was used, but it was negligible when conventional rolling was used. The strengthening gained through the homogeneous dispersion of high-density nanosized MLG particles in the HRDSR-processed composites was attributed to Orowan strengthening. This finding is different from the HRDSR-processed carbon-nanotube (CNT)/Cu composites studied in our previous work, in which the grain-size reduction through the addition of CNTs was the major contribution to the strengthening effect.