Protective Graphite Coating for Two-Dimensional Carbon/Carbon Composites

Two-dimensional carbon/carbon(2D C/C)composites are a special class of carbon/carbon composites,generally obtained by combining resin-impregnated carbon fiber clothes,which are then cured and carbonized.This study deals with the preparation of a protective coating for these materials.This coating,based on graphite,was prepared by the slurry method.The effect of graphite and phenolic resin powders with different weight ratios was examined.The results have shown that the coating slurry can fill the pores and cracks of the composite surface,thereby densifying the surface layer of the material.With the increase of the graphite powder/phenolic resin weight ratio,the coating density is enhanced while the coating surface flatness decreases;moreover,the protective ability of coating against erosion first increases(from 1:3 to 2:2)and then decreases(from 2:2 to 3:1).When the weight ratio is about 1:1,the coating for 2D C/C composites exhibits the best erosion resistance,which greatly aids these materials during gas quenching.In this case,the erosion rate is decreased by approximately 41.5%at the impact angle of 30°and 52.3%at normal impact,respectively.This can be attributed to the ability of the coating slurry to infiltrate into the substrate,thereby bonding the fibers together and increasing the compactness of the 2D C/C composites.

Effect of WS_2 addition on electrical sliding wear behaviors of Cu-graphite-WS_2 composites

Four kinds of Cu-based composites with different mass ratios of graphite and WS2 as lubricants were fabricated by hot-pressing method. Electrical sliding wear behaviors of the composites were investigated using a block-on-ring tribometer rubbing against Cu-5%Ag alloy ring. The results demonstrated that 800 ~C was the optimum sintering temperature for Cu-graphite-WS2 dual-lubricant composites to obtain the best comprehensive properties of mechanical strength and lubrication performance. Contact voltage drops of the Cu-based composites increased with increasing the mass ratio of WS2 to graphite. The Cu-based composite with 20% graphite and 10% WS2 showed the best wear resistance due to the excellent synergetic lubricating effect of graphite and WS2. The reasonable addition of WS2 into the Cu-graphite composite can remarkably improve the wear resistance without much rise of electrical energy loss which provides a novel principle of designing suitable sliding electrical contact materials for industrial applications.

Recent Advances in Interface Modification of Cu/graphite Composites and Layered Ternary Carbides of Modified Layer Candidate

We review the fundamental properties and significant issues related to Cu/graphite composites.In particular,recent research on the interfacial modification of Cu/graphite composites is addressed,including the metal-modified layer,carbide-modified layer,and combined modified layer.Additionally,we propose the use of ternary layered carbide as an interface modification layer for Cu/graphite composites.

Enhanced Thermal Conductivity and Bending Strength of Graphite Flakes/aluminum Composites Via Graphite Surface Modification

The effect of graphite surface modification on the thermal conductivity(TC) and bending strength of graphite flakes/Al composites(Gf/Al) prepared by gas pressure infiltration were investigated. Al3 Ni and Al4C3 phase may form at the interface in Ni-coated Gf/Al and uncoated Gf/Al composites, respectively, while the Al-Cu compound cannot be observed in Cu-coated Gf/Al composites. The Cu and Ni coatings enhance TC and the bending strength of the composites in the meantime. TC of Cu-coated Gf/Al composites reach 515 Wm^-1·K^-1 with 75 vol% Gf, which are higher than that of Ni-coated Gf/Al. Meanwhile, due to Al3 Ni at the interface, the bending strength of Ni-coated Gf/Al composites are far more than those of the uncoated and Cu-coated Gf/Al with the same content of Gf. The results indicate that metal-coated Gf can effectively improve the interfacial bonding between Gf and Al.

Effect of graphite powder as a forming filler on the mechanical properties of SiCp/Al composites by pressure infiltration

（38vo1% SiCp ＋ 2vo1% A1203f）/2024 A1 composites were fabricated by pressure infiltration. Graphite powder was introduced as a forming filler in preform preparation, and the effects of the powder size on the microstructures and mechanical properties of the final com- posites were investigated. The results showed that the composite with 15 μm graphite powder as a forming filler had the maximum tensile strength of 506 MPa, maximum yield strength of 489 MPa, and maximum elongation of 1.2%, which decreased to 490 MPa, 430 MPa, and 0.4%, respectively, on increasing the graphite powder size from 15 to 60 μm. The composite with 60 μm graphite powder showed the highest elastic modulus, and the value decreased from 129 to 113 GPa on decreasing the graphite powder size from 60 to 15 μm. The differences between these properties are related to the different microstructures of the corresponding composites, which determine their failure modes.

Microstructure and properties of high-fraction graphite nanoflakes/6061Al matrix composites fabricated via spark plasma sintering

30-50 wt.%graphite nanoflakes(GNFs)/6061Al matrix composites were fabricated via spark plasma sintering(SPS)at 610℃.The effects of the sintering pressure and GNF content on the microstructure and properties of the composites were investigated.The results indicated that interfacial reactions were inhibited during SPS because no Al4C3 was detected.Moreover,the agglomeration of the GNFs increased,and the distribution orientation of the GNFs decreased with increasing the GNF content.The relative density,bending strength,and coefficient of thermal expansion(CTE)of the composites decreased,while the thermal conductivity(TC)in the X−Y direction increased.As the sintering pressure increased,the GNFs deagglomerated and were distributed preferentially in the X−Y direction,which increased the relative density,bending strength and TC,and decreased the CTE of the composites.The 50wt.%GNFs/6061Al matrix composite sintered at 610℃ under 55 MPa demonstrated the best performance,i.e.,bending strength of 72 MPa,TC and CTE(RT−100℃)of 254 W/(m·K)and 8.5×10^(−6)K^(−1)in the X−Y direction,and 55 W/(m·K)and 9.7×10^(−6)K^(−1)in the Z direction,respectively.

Composites on Base of the Ultradispersed Polytetrafluoroethylene and Graphite Oxide Intercalated Compounds

Composites based on ultradispersed polytetrafluoroethylene and intercalated graphite oxide compounds with dodecahydro-closo-dodecaborates and methods of their fabrication have been developed. The fabricated composites have been characterized using XRD analysis, and optical microscopy. These composites are distinguished with completeness of their combustion, since the combustion products comprise gaseous boron fluorine-containing compounds of boron, boron trifluoride (BF3), and boron oxyfluoride ((BOF)3). Besides, these composites are characterized with increased energy capacity as compared to purely oxygen-containing compounds, since the heat of formation of boron fluorine-containing compounds is higher than that of boron oxide. Introduction of ultradispersed polytetrafluoroethylene imparts composites with hydrophobicity, thus improving their functioning properties.

Tribological behaviors of Ag-graphite composites reinforced with spherical graphite

Two kinds of Ag-graphite composites reinforced with spherical graphite(SG)and conventional flake graphite(FG)were prepared by powder metallurgy technology.The effect of graphite morphology on the tribological behavior for the Ag-SG and Ag-FG under the dry sliding wear was investigated with a pin-on-disk tribometer at a load of 3.0 N in atmosphere condition.The results indicated that the minimum wear rate of 3.5×10^-5 mm^3/(N·m)for Ag-FG was achieved and it reduced by nearly an order of magnitude,reaching 1.6×10^-6 mm^3/(N·m)for the Ag-SG.The obviously different tribological behaviors between the Ag-SG and Ag-FG were closely related to the formation of cracks in the sub-surface.The stress concentration tended to generate at the edges of flake graphite during sliding process,which resulted in the cracks and severe delamination wear of Ag-FG.However,no cracks were found around the spherical graphite in Ag-SG.The spherical graphite can effectively inhibit the initiation and propagation of cracks,achieving high wear resistance.

Sintering behavior and thermal conductivity of nickel-coated graphite flake/copper composites fabricated by spark plasma sintering

Nickel-coated graphite flakes/copper（GN/Cu） composites were fabricated by spark plasma sintering with the surface of graphite flakes（GFs） being modified by Ni–P electroless plating. The effects of the phase transition of the amorphous Ni–P plating and of Ni diffusion into the Cu matrix on the densification behavior, interfacial microstructure, and thermal conductivity（TC） of the GN/Cu composites were systematically investigated. The introduction of Ni–P electroless plating efficiently reduced the densification temperature of uncoated GF/Cu composites from 850 to 650℃ and slightly increased the TC of the X–Y basal plane of the GF/Cu composites with 20 vol%–30 vol% graphite flakes. However, when the graphite flake content was greater than 30 vol%, the TC of the GF/Cu composites decreased with the introduction of Ni–P plating as a result of the combined effect of the improved heat-transfer interface with the transition layer, P generated at the interface, and the diffusion of Ni into the matrix. Given the effect of the Ni content on the TC of the Cu matrix and on the interface thermal resistance, a modified effective medium approximation model was used to predict the TC of the prepared GF/Cu composites.

Evaluation of sliding wear behavior of graphite particle-containing magnesium alloy composites

The influence of graphite particle content on the friction and wear characteristics of AZ91 magnesium alloy matrix composite was studied. The results show that the wear resistances of graphite-containing composite are much better than those of the matrix under the test conditions. The anti-wear ability of magnesium alloy composite is improved substantially with the increase of the graphite content from 5% to 20%, and both wear mass loss and coefficient of friction are decreased to low level. Different wear mechanisms operate at different sliding stages. A continuous black lubricating film forms progressively on the worn surface along sliding, which effectively limits the direct interaction between the composite tribosurface and the counterpart, and also remarkably delays the transition from mild wear to severe wear for magnesium alloy composite.

Microstructures and wear properties of graphite and Al_2O_3 reinforced AZ91D-Cex composites

The magnesium matrix composites reinforced by graphite particles and Al2O3 short fibers were fabricated by squeeze-infiltration technique.The additions dispersed uniformly and no agglomeration and casting defect were observed.The microstructures and wear properties of the composites with different Ce contents of 0,0.4%,0.8%and 1.0%,respectively,were investigated.Especially,the effect of Ce on the properties was discussed.The results reveal that Ce enriches around the boundaries of graphite particles and forms Al3Ce phase with Al.The addition of Ce refines the microstructures of the composites.With the increase of Ce content,the grain size becomes smaller and the wear resistance of the composite is improved.At low load,the composites have similar worn surface.At high load,the composite with 1.0%Ce has the best wear resistance due to the existence of Al3Ce phase.The Al3Ce phase improves the thermal stability of the matrix so the graphite particles can keep intact,which can still work as lubricant. At low load,the wear mechanism is abrasive wear and oxidation wear.At high load,the wear mechanism changes to delamination wear for all the composites.

Effect of graphite content on wear property of graphite/Al_2O_3/Mg-9Al-1Zn-0.8Ce composites

Using squeeze-infiltration technique, Mg-9Al-1Zn-0.8Ce composite reinforced by graphite particles and Al2O3 short fibers was fabricated. The reinforcing phases combined closely with the matrix and no agglomeration was observed. The microstructure, hardness and wear property of the composites with the graphite content of 5%, 10%, 15% and 20% were investigated, respectively. The results reveal that Ce tends to enrich around the boundaries of graphite particles and Al2O3 short fibers, and forms Al3Ce phase. When the graphite content increases to 20%, the grain size becomes small. Moreover, with increasing the graphite content, the microhardness of the composites decreases but the wear resistance increases. The graphite which works as lubricant during dry sliding process decreases the wear loss. At low load, the wear mechanism of the composite is mainly abrasive wear and oxidation wear; at high load, except that the composite with 20% graphite is still with abrasive wear and oxidation wear, the wear mechanism of other composites changes to delamination wear.

Effect of graphite particle size on wear property of graphite and Al_2O_3 reinforced AZ91D-0.8%Ce composites

The graphite particles and Al_2O_3 short fibers reinforced AZ91D-0.8%Ce composites were fabricated by squeeze-infiltration technique.The researches about the effects of different graphite particle sizes on the microstructure and wear property of the composites were performed under the condition of constant contents of graphite particles and Al_2O_3 short fibers.The results reveal that the grain size of the composites changes less when the graphite particle size descends.Moreover,Ce enriches around the graphite particle and Al_2O_3 short fibers and forms Al_3Ce phase with A1 element.The graphite that works as lubricant decreases the wear loss.The wear resistance of the composites increases as the graphite particle size increases.At low load the composites have similar wear loss;at high load the composite with the largest graphite particle size has the best wear resistance.The wear mechanism of all the composites at low load is abrasive wear and oxidation wear;at high load,except the composites with the particle size of 240μm whose wear mechanism is still abrasive wear and oxidation wear,the wear mechanism of others changes to delamination wear.

Tribological properties of Ni-base alloy composite coating modified by both graphite and TiC particles

In order to reduce the friction coefficient of Ni-base alloy coating and further improve its wear resistance,Ni-base alloy composite coatings modified by both graphite and TiC particles were prepared by plasma spray technology on the surface of 45 carbon steel.The results show that friction coefficient of the composite coating is 47.45% lower than that of the Ni-base alloy coating,and the wear mass loss is reduced by 59.1%.Slip lines and severe adhesive plastic deformation are observed on the worn surface of the Ni-base alloy coating,indicating that the wear mechanisms of the Ni-base alloy coating are multi-plastic deformation wear and adhesive wear.A soft transferred layer abundant in graphite and ferric oxide is developed on the worn surface of the composite coating,which reduces the friction coefficient and wear loss in a great deal.The main wear mechanism of the composite coating is fatigue delamination of the transferred layer.

Lithium Storage Property of Graphite/AlCuFe Quasicrystal Composites

Quasicrystals have long-range quasi-periodic translational ordering and non-crystallographic rotational symmetry.Al-Cu-Fe quasicrystals have great potential for lithium storage because of their high Al content and a large number of defects in the structure.In our previous study(J.Alloys Compd.805(2019)942)we showed that Al-Cu-Fe quasicrystals have good initial capacity whereas its cycle stability is poor.In the present study,graphite/AlCuFe is prepared by the mechanical alloying method.The results show that graphite/AlCuFe quasicrystal composites are successfully synthesized by planetary ball milling at 550 rpm for 80 h.The quasicrystal particle size decreases and the amorphous graphite forms onion-like carbon(OLC)when the two phases mix evenly.OLC forms on the surface of the Al-Cu-Fe quasicrystalline powder.Charge and discharge tests show that graphite/AlCuFe quasicrystal composites have high-stability capacity of 480 mAh/g after 20 cycles,which is larger than the sum of capacities of graphite and Al-Cu-Fe quasicrystals.

Tribological behavior and mechanisms of graphite/CaF_2/TiC/Ni-base alloy composite coatings

In order to reduce the friction coefficients and improve the wear resistance of mechanical parts, which work in the severe friction and wear conditions at heavy loads, the graphite/CaFg/TiC/Ni-base alloy composite coatings were prepared by plasma spray and their tribological behavior and mechanisms were investigated. The results show that the friction coefficients of the composite coatings are in the range of 0.22-0.288, which are reduced by 25.9% to 53% compared with those of the pure Ni-base alloy coatings, and the wear rates of the former are 18.6%-70.1% less than those of the latter. When wear against GCr15 steel balls, a transferred layer mainly composed of ferric oxides, graphite and CaF2 may gradually develop on the worn surface of the composite coatings, which made the friction and wear between GCr15 steel ball and the composite coatings change into that between the former and the transferred layer. So the friction coefficients and the wear lubrication effect of the transferred layer. The main wear layer in friction process. rates of the composite coatings are greatly reduced because of the solid mechanism of the composite coatings is delamination of the transferred

Effects of graphite content on microstructure and tribological properties of graphite/TiC/Ni-base alloy composite coatings

In order to reduce the friction coefficients and further improve the anti-wear properties of Ni-base alloy coatings reinforced by TiC particles,graphite/TiC/Ni-base alloy（GTN） coatings were prepared on the surface of 45 carbon steel.The effects of graphite content on the microstructure and tribological properties of the GTN coatings were investigated.The results show that the addition of graphite to the GTN coatings may greatly reduce the friction coefficients and improve their wear resistance.The 6.56GTN and 12.71GTN coatings exhibit excellent integrated properties of anti-friction and wear resistance under low and high loads,respectively.Under a low load,the wear mechanisms of the GTN coatings are mainly multi-plastic deformation with slight abrasive wear and gradually change into mixture of multi-plastic deformation,delamination and micro-cutting wear with the increase of graphite fraction.As the load increases,the main wear mechanisms gradually change from micro-cracks,micro-cutting and adhesive wear to micro-cutting and micro-fracture with the increase of graphite fraction.

Preparation and electrochemical properties of Co_3O_4/graphite composites as anodes of lithium ion batteries

Co3O4/graphite composites were synthesized by precipitation of cobalt oxalate on the surface of graphite and pyrolysis of the precipitate, and the effects of graphite content and calcination temperature on the electrochemical properties of the composites were investigated. The samples were characterized by thermogravimetry and differential thermal analysis （TG/DTA）, X-ray diffractometry （XRD）, scanning electron microscopy （SEM）, cyclic voltammetry （CV）, electrochemical impedance spectroscopy （EIS） and charge/discharge measurements. With increasing the graphite content, the reversible capacity of the Co3O4/graphite composites decreases, while cycling stability improves dramatically, and the addition of graphite obviously decreases the average potential of lithium intercalation/deintercalation. The reversible capacity of the composites with 50% graphite rises from 583 to 725 mA-h/g as the calcination temperature increases from 300 to 500 ℃, and the Co304/graphite composites synthesized at 400 ℃ show the best cycling stability without capacity loss in the initial 20 cycles. peaks, corresponding to the lithium intercalaction/deintercalation for The CV profile of the composite presents two couples of redox graphite and Co3O4, respectively. EIS studies indicate that the electrochemical impedance decreases with increasing the graphite content.