Nickel-coated Graphite Research Articles

Tribological analysis and machine learning modeling of nickel-coated graphite reinforced A206 metal matrix composites

Tribological analysis and machine learning modeling of nickel-coated graphite reinforced A206 metal matrix composites

Microstructure and properties behavior of in situ synthesized with high content (Ti, W) C reinforced In625 by two step-laser direct energy deposition

The formation of sensitive interface cracks and the difficulty in processing high-concentration Ni-based ceramic coatings via direct energy deposition (LDED) present major engineering challenges. To address these, high-quality In625/ceramic coatings with various mass contents of Ti, nickel-coated graphite (Ni3C), and WC were fabricated on QT250 using two-step laser directed energy deposition (TsLDED). The influence of the Ti/C: WC molar mass ratio on the bonding interface, microstructure, phase composition, and mechanical properties of the coatings was analyzed. The results indicated that grains at the In625/ceramic coating interface formed epitaxial growth, ensuring a robust bond. In situ synthesis of (Ti, W) C, WCx (WC and W2C), M23C6, and other precipitated phases were uniformly distributed, enhancing nucleation, refining microstructure, and improving mechanical properties. The addition of Ti facilitated the transformation of WCx to (Ti, W) C. High Ti and C concentrations promoted eutectic structure formation in the matrix phase, enhancing performance. The In625 + 56 % Ti – 14 % Ni3C – 30 % WC composite coating exhibited the highest microhardness and the lowest friction coefficient, with microhardness 5.61 and 3.6 times that of QT250 and In625 coatings, respectively, and a friction coefficient 0.3 times that of In625. Variations in the Ti/C: WC molar mass ratio directly affected the content, proportion, and type of (Ti, W) C, WCx, γ-Ni, and eutectic structures comprising M23C6, NiTix, Ni2W4C, Cr2Ti, and γ-Ni, influencing microstructure evolution and mechanical properties. The TsLDED process thus enables the preparation of In625/ceramic reinforced coatings with improved mechanical properties.

Tribological properties of atmospheric plasma sprayed Cr3C2–NiCr/20% nickel-coated graphite self-lubricating coatings

Using atmospheric plasma spraying technology, Cr3C2–NiCr (CN)and Cr3C2–NiCr/20 % Nickel-coated graphite (CG) composite coatings were successfully deposited on 304 stainless steel substrates, with three different spraying distance parameters designed to optimize the experiment. The study investigated the influence of nickel-coated graphite on the structure, hardness, porosity, and friction-wear performance of the composite coatings. Wear mechanisms were investigated based on analyses of morphologies and chemical states of the worn surfaces of the CG composite coatings. Our results demonstrate that the CG coating exhibits lower friction coefficients, ranging from 0.24 to 0.28, than that of the CN coating. The incorporation of nickel-coated graphite leads to formation of a solid-lubricating film at friction interface, lowering friction and wear. What's more, presence of nickel-coated graphite mitigates brittleness of the CN coating, as is deemed important for improving abrasion resistance of the coatings.

Tribological investigation into nickel-coated graphite polytetrafluoroethylene composites

The friction and wear resistance of polytetrafluoroethylene (PTFE) composites can be enhanced by incorporating nickel-coated graphite. An electroless coating method employing Gin plates (418A, 418B) is utilized to produce nickel-coated graphite. X-ray diffractometer analysis reveals the presence of nickel and graphite peaks in the coated graphite powders at 44° and 26.4°, respectively. Scanning electron microscopy images confirm the presence of nickel coating on graphite particles. Tribological tests using a pin-on-disc tribometer (L9) demonstrate that composites filled with 20 wt.% Nickel-coated graphite exhibits the lowest wear rate of 220 µm, compared to 1166 µm for pure PTFE specimens. The notable improvement in wear resistance is attributed to enhanced bonding strength between the filler and matrix material. Pure PTFE exhibits varying coefficient of friction (CoF) at different parameters, with the highest and lowest CoF observed at 200 rpm, 20N and 180 rpm, 10 N, respectively. Optimal parameters for minimizing wear rate and CoF, determined through analysis of means, include a 20 wt.% filler concentration, disc speed of 180 rpm, and 10N load. Analysis of variance identifies composition and speed as primary factors affecting wear and CoF.

The effects of in-situ synthesized TiC on the performance improvement of nickel-based composite coatings for rail repair

With the increase in train speed and axle weight, the quality and service life of the rail (U71Mn steel) are more demanding. Aiming at the excellent properties of nickel/nickel-based alloys and ceramic materials, this paper prepares TiC/Ni45 composite coatings for rail repair by in-situ synthesis of ceramic phases using laser cladding technology. The effects of in-situ synthesized TiC on the physical phase, microstructure, microhardness and wear resistance were investigated and discussed in detail. The results show that the reaction of in-situ synthesized TiC can proceed positively, and the microstructure of the cladding layer mainly consists of the segregation of Cr, TiC particles, and substrate phase. With the increase of nickel-coated graphite and titanium powder, the average microhardness value of the cladding layer increased, and the average friction coefficient and wear volume decreased. When the mass fraction of (Ti + C) reaches 15 wt%, the average friction coefficient of the cladding layer reaches the minimum value. When the mass fraction reaches 20 wt%, the average microhardness of the cladding layer reaches 2.65 times that of the substrate, and the wear mechanism is transformed from mainly adhesive wear to abrasive, oxidative, and fatigue wear.

STRUCTURE AND PROPERTIES OF SELF-LUBRICATING COPPER-NICKEL-GRAPHITE COATING FABRICATED USING COLD SPRAY

Application of self-lubricating Cu-matrix coatings is an attractive way to provide high electrical conductivity and wear performance in contact friction pairs in various areas of modern engineering. In the present work, the structure and properties of self-lubricating copper-nickel-graphite coating deposited on copper substrate using high-pressure cold spray were studied for the first time. The coating was fabricated by spraying dendritic copper and flaked nickel-coated graphite powders mixed in a ratio 70/30 wt.%, which ensured the formation of a lamellar structure. The obtained coating exhibited an attractive combination of hardness (108.8 HV1), coefficient of friction (0.34) and electrical conductivity (43.8 % IACS), which open prospects for its electrical applications.

Study of nickel-coated graphite/silicone rubber composites for the application of electromagnetic interference shielding gaskets

This study aimed to produce electromagnetic interference (EMI) gaskets by combining silicone rubber and nickel-coated graphite as the matrix and filler, respectively. Scanning electron microscopy (SEM) images revealed the rough surface of the gaskets, indicating the appropriate distribution of filler powders within the polymer matrix. The experiment involved three samples containing 30%, 50%, and 70% filler by weight. The results showed that as the filler content increased, the electrical resistivity of the gaskets decreased, while their hardness increased. Moreover, the shielding effectiveness of the gaskets was observed to exceed 55 dB.m within the frequency range of 1.2 to 2.6 GHz.

Effect of N–Ni coordination bond on the electrical and thermal conductivity of epoxy resin/nickel‐coated graphite

AbstractThe agglomeration of nickel‐coated graphite (NCG) in epoxy resin (EP) composites leads to low electrical conductivity of EP composites, which limits their development in electronic devices and multilayer circuits. In order to improve the electrical and thermal conductivity of NCG/EP composites, ethylenediamine (EDA) was used to modify NCG and compared with pure NCG‐filled EP composites. It was found that the conductive effect of modified composites with 20 wt% filler is better than that of unmodified composites with 40 wt% filler. The results of Fourier transform infrared spectroscopy and thermogravimetric analysis of EDA‐modified NCG (ENCG) showed that a coordination adsorption reaction occurred between EDA and NCG, forming N–Ni coordination bonds. When the filling amount of ENCG was 40 wt%, the conductivity and thermal conductivity of the composite are improved most significantly. The volume resistivity was reduced from 2.636 to 0.109 Ω cm, a decrease of 95.85%, and the thermal conductivity was improved from 0.517 to 0.968 W/(m K), an increase of 87.23%, respectively. Meanwhile, ENCG has better dispersion in the EP matrix than NCG.

Microstructure and high temperature wear behavior of in-situ synthesized carbides reinforced Mo-based coating by laser cladding

To broaden the application fields of Mo coating as wear resistant coatings for hot-end components in jet engines, the in-situ synthesized carbides reinforced Mo-based coatings were prepared by laser cladding. The effect of nickel-coated graphite (carbon source) on the microstructure, hardness and elevated-temperature wear behavior of coatings was studied. The wear behavior of coatings was evaluated by using a tribotester with a ball-on-disc configuration from room temperature to 1000 °C against Si3N4 ball in air. The results showed that the carbides played a role of dispersion-strengthening. The coatings were composed of Mo, Cr1.12Ni2.88, Cr9Mo21Ni20, Mo2C, Cr7C3 and Mo6Ni6C. The wear resistance of the laser clad coatings was significantly enhanced by the addition of nickel-coated graphite, and the wear rates firstly decreased and then increased with increasing graphite content. The friction coefficients of laser clad coatings increased with an increase in nickel-coated graphite content. There existed a critical content of nickel-coated graphite that best strengthened the tribological behavior from room temperature to 1000 °C. The coating with 6.0 wt% nickel-coated graphite exhibited favorable tribological properties due to the moderate ductility, carbides, lubricating layer and in-situ synthesized solid lubricants.

Mechanical and Tribological Behavior of LM26/SiC/Ni-Gr Hybrid Composites

The study evaluates the mechanical and wear properties of LM26 alloy and its hybrid composites with silicon carbide (SiC) and nickel-coated graphite (Ni-Gr). LM26 aluminum alloy is generally known for its high strength, wear, and corrosion resistance compared to similar materials such as zinc and magnesium. The effect of Ni-Gr was studied, with 2 wt.% was found to provide the best mechanical properties. LM26 composites reinforced with varying percentages of SiC (0 to 30 wt.%) showed the best properties at 20 wt.% reinforcement after fabrication using a bottom pouring type stir casting setup (Two step feeding method). Evaluation of five hybrid LM26 composites through tensile strength, elongation, hardness, impact, porosity, and thermal studies showed that the LM26/2 wt.% Ni-Gr/20 wt.% SiC configuration showed the best filler composition for improved strength. Sliding wear evaluation using experimental and Taguchi analysis was performed at different configurations to identify the best wear resistance. Microstructure studies showed the presence of Ni-Gr particles forming coatings and temperature playing a significant role in the progression of the wear rate. Furthermore, the hybrid composite with 20% SiC and 2% Ni-Gr reinforcement showed the best wear resistance.

Highly flexible composite with improved Strain-Sensing performance by adjusting the filler network morphology through a soft magnetic elastomer

Elastomer-based composites are promising materials for stretchable strain sensors. Herein, a soft magnetic elastomer with alternating south (S) and north (N) poles (often used as a soft magnet for common use) induced randomly distributed nickel coated graphite (NCG) along the magnetic lines at the mold bottom within 2 s. Polydimethylsiloxane (PDMS) was casted to peel off and encapsulate the NCG layer. NCG pellets were upright at the N or S poles, whereas they were laid down between the N and S poles. Thus, the pellets formed networks with a sensitive vertical loose network and stable horizontal tight network. The electrical conductivity, sensitivity, and working strain range of the obtained composite increased by two orders, one order of magnitude and twice, respectively, compared with PDMS/NCG with a random distributed NCG. This enhancement of sensing behavior was confirmed theoretically by the disconnection, tunneling, and hopping effects for the resistance change during elongation.

Novel Silver-Plated Nickel-Coated Graphite Powder with Excellent Heat and Humidity Resistance: Facile Preparation and Performance Investigation.

Nickel-coated graphite (Ni/C) powder has many applications in diverse areas such as paint, print ink, adhesive, conductive rubber, and so on. To increase its stability in harsh environmental conditions, the electroless plating of silver film on Ni/C via ascorbic acid was studied. A silver layer with a thickness of 2.5 μm was successfully plated on Ni/C powder’s surface with an Ag loading of 44.35 wt.%. Silica gel blended with the Ag/Ni/C powder exhibited much higher conductivity under aging conditions of 85 °C and 85% RH for 1000 h than that with pristine Ni/C powder. Further tests showed that the conductivity of Ag/Ni/C powder remained almost unchanged even in an extremely humid and hot condition for 1000 h. Aging tests were carried out for Ag/Ni/C and Ni/C powders under long-term humid and hot conditions (85 °C, 85% RH), in which Ag/Ni/C samples showed much better electromagnetic shielding performance. Due to the excellent properties and reasonable price, the potential applications of Ag/Ni/C in conductive glue and electromagnetic shielding glue could be expected.

Effect of TiB2 Content on Properties of Nickel-Coated Graphite Self-Lubricating Coating Prepared by Laser Cladding

To improve the anti-wear and friction-reducing properties of self-lubricating coatings, Ni60/Nickel-coated graphite/TiB2 composite coatings with different contents were prepared by laser cladding. The coating properties were characterized by X-ray diffractometer (XRD), scanning electron microscope (SEM), energy spectrometer (EDS), electrochemical workstation, micro-Vickers hardness tester, and friction and wear tester. The results showed that with the increase in TiB2 content, the graphite morphology changed from spherical at 0 wt.% TiB2 content to a little black graphite alone at 14 wt.% TiB2 to irregular agglomerates at 22 wt.% TiB2. Furthermore, the hardness of the coatings increased with increasing TiB2 content, and the 63% Ni60 + 15% nickel-coated graphite + 22% TiB2 coating had the highest hardness. TiC and Cr7C3 were generated in the coatings with the addition of nickel-coated graphite, creating a dispersion reinforcement effect, so that the hardness of these coatings was higher than that of the 86% Ni60 + 0% nickel-coated graphite + 14% TiB2 coating without the addition of nickel-coated graphite. In addition, the 71% Ni60 + 15% Ni-coated graphite + 14% TiB2 coating had the lowest friction coefficient, wear loss, and wear volume, thus exhibiting excellent friction reduction and anti-wear properties. The 71% Ni60 + 15% nickel-coated graphite + 14% TiB2 coating had excellent corrosion resistance.

The tunable sensing behaviors of flexible conductive PDMS/NCG composites via regulation of filler size prepared by a facile sedimentation method

Flexible strain sensing composites with tunable behaviors are widely required in fields such as telemedicine, wearable health monitoring equipment, and electronic skin. In this study, the sensing behaviors of flexible conductive polydimethylsiloxane (PDMS)/nickel-coated graphite (NCG) composites were easily regulated by adjusting the NCG size, in which the composites were prepared by a facile sedimentation method. The size of NCG particles has a significant impact on the sensing performances, including resistance change against strain and working range. When the size was small (1 and 30 μm), the resistance of PDMS/NCG slightly increased, then decreased clearly, and finally rose with increasing strain again. On the other hand, the resistance of PDMS/NCG increased monotonously with strain when the size was large (80 and 100 μm). The working range decreased with increments of filler size. Then, resistance of composites against strain was easily tuned by changing the content ratio of hybrid fillers with NCG of 30 μm and 100 μm. It was due to the competition between the resistance change along and perpendicular to the stretching direction which was proved by the morphology revolution and sensing performance of composites with hybrid fillers. The composite sensors could realize the detection of human motion. The results show that the controls of filler size and synergy effects of the hybrid fillers with different sizes are efficient ways to regulate the sensing behaviors of flexible sensors.

Microstructure and properties characterization of Ti-containing Ni60/Graphite self-lubricating composite coatings applied on 300M ultra-high strength steel by laser cladding

To improve the wear and corrosion resistance of 300M ultra-high strength (300M) steels, the Ni-based alloy (Ni60)/nickel-coated graphite composite coatings with the addition of titanium (Ti) were claded on 300M by laser. The microstructure, micro-hardness, tribological performance, corrosion resistance, thermal property, and dynamic mechanical property of the coatings were characterized. The cladding-layer microstructure of the Ti-containing (6 wt% Ti) coatings showed an equiaxial tendency. The microhardness of the Ti-containing coatings was higher and more homogeneous. The wear rate of the matrix was 29.4 times higher than that of Ti-containing composite coatings and was 2.4 times larger than that of the Ti-free (0 wt% Ti) composite coatings. However, the friction coefficient of the Ti-containing composite coatings was higher than that of the Ti-free composite coatings. The self-corrosion current densities of the Ti-containing, Ti-free composite coating and 300M were 0.25, 3.16 and 232.51 μA/cm2, respectively, indicating that the corrosion resistance of Ti-containing composite coatings was improved. The impact-resistance of the Ti-containing composite coatings was better than that of the Ti-free composite coatings.

Tribological characterization of LM26/SiC/Ni.-Gr. Hybrid aluminium matrix composites (HAMCs) for high temperature applications

In this study, tribological characteristics of the hybrid composite material LM26/ SiC / Ni.-Gr. were studied under different temperature conditions. The LM26 aluminum alloy was reinforced with silicon carbide (SiC) with various weight fractions (0%, 10% and 20%) by keeping nickel-coated graphite (Ni.-Gr.) constant at 2%. Using stir casting setup wear test samples were prepared. Pin on disk equipment was used to assess the tribological performance of both pure aluminum alloy and hybrid composites on the basis of wear loss and friction coefficient. Further, the plan order for performing trials was developed with design of experiments (DOE) and analysis of variance (ANOVA) tools. It was found that the composite's tribological and mechanical performance under high temperature sliding wear conditions was improved because of the hybridization of hard and soft reinforcements. Experimental results revealed that load and temperature primarily affect both pure aluminum alloys and hybrid composites performance. Also low wear loss and friction coefficient were obtained during high-temperature wear tests. The LM26 + 20% SiC + 2%Ni.-Gr.hybrid composite showed the highest improvement in tribological performance. Worn surface analysis using SEM technique showed that hybrid reinforcement significantly increases wear resistance in hybrid aluminum composites. These findings indicate that the proposed hybrid aluminum composites can be considered as an alternative material in which wear-resistant and high-strength components are of primary importance in the automotive industry.

Fabrication of highly conducting nickel-coated graphite composite particles with low Ni content for excellent electromagnetic properties

Nickel-coated flaky graphite particles (FGP@NiCPs) have been widely employed as key fillers of electromagnetic functional composites. However, the existing such fillers suffer from disadvantages of uncompacted shells, unsatisfactory conductivity or high nickel content, making it hard to meet high requirements for electronic connection and electromagnetic compatibility. Herein, we have demonstrated an efficient approach to achieving sufficiently heterogeneous nucleation coupled with electroless Ni plating to fabricate highly conducting FGP@NiCPs with low Ni content for excellent electromagnetic properties of polymer-matrix composites. Preparation of the typical FGP@NiCPs consists of rinsing flaky graphite particles (FGPs), adsorbing nickel ions, in-situ reduction into nickel nuclei and electroless Ni plating. On the one side, the hydrophilicity of FGPs can be improved by soxhlet extraction. This is one of important factors to adsorb more nickel ions on FGPs because they can be uniformly dispersed or fully exposed to NiSO 4 solution. On the other side, the rinsed FGPs are immersed into a high concentration ([NiSO 4 ]) solution, which facilitates to further adsorb enough nickel ions through electrostatic attraction. Subsequently, these nickel ions adsorbed on FGPs are in-situ reduced into a lot of nickel nuclei, indicating that increasing hydrophilicity and immersing into a high [NiSO 4 ] for FGPs synergistically favor heterogeneous nucleation burst. Finally, low content nickel densely-coated FGPs composite particles are successfully synthesized by controllable electroless Ni plating. As-obtained FGP@NiCPs exhibit dense shells, low Ni content and excellent electrical conductivity compared to the commercial FGP@NiCPs (CFGP@NiCPs). Furthermore, shielding effectiveness of composites containing the typical FGP@NiCPs is between 28.0 and 35.2 dB with frequency of electromagnetic wave ranging from 30 to 1500 MHz, and stronger than that of composites containing CFGP@NiCPs, owing to the relatively high electrical conductivity. Consequently, this work holds a promising potential for electromagnetic functional polymer-matrix composites. Increasing hydrophilicity and immersion into a high concentration of NiSO 4 solution for FGPs synergistically favor nucleation burst, which is advantageous to fabricate low content Ni densely-coated FGPs composite particles for excellent electromagnetic properties of their polymer-matrix composites. • Hydrophilicity of flaky graphite particles (FGPs) can be improved by soxhlet extraction. • Increasing hydrophilicity and immersion into a high concentration of NiSO 4 solution for flaky graphite particles (FGPs) favor nucleation burst. • Sufficient heterogeneous nucleation facilitates to fabricate low content Ni densely-coated FGPs with high conductivity. • As-obtained composite particles promise important applications in electronic connection and electromagnetic compatibility.

Facile one-step preparation of laminated PDMS based flexible strain sensors with high conductivity and sensitivity via filler sedimentation

Rubber based conductive composites with laminated structures are promising approaches to prepare flexible sensors with high performance abilities. Herein we report a facile one-step method to prepare polydimethylsiloxane (PDMS) based flexible strain sensors with a laminated structure via filler sedimentation. Nickel coated graphite (NCG) conductive fillers were homogenosly dispersed into a PDMS solution and then allowed to form a sedimention layer by allowing the mixture to stand for 2 h to obtain composite sensors. PDMS/NCG composites presented a two dimensional conductive network with a low percolation value of 2.52 vol% and high conductivity of 148 S/m at 11.11 vol% NCG. Due to the laminated structure, the Younge's modulus of the composites increased from 0.88 MPa for pure PDMS to only 1.98 MPa for 11.11 vol% NCG indicating high flexibility. Under applied stress, composite resistances increased from 8 to 20 Ω (varied by vol% NCG) to 4 × 108 Ω and presented a gauge factor (GF) of 5.6 × 108, amongst the highest values when compared with published results. Composite resistance under strain is explained by constriction, tunneling, and hopping mechanisms, and experimental results agree well with theoretical values. Filler sedimentation is demonstrated to be a valuable method to produce highly conductive and sensitive rubber based, laminated flexible sensors requiring only one preparation step.

A comprehensive study of metal-coated short carbon fibers, graphite particles, and hybrid fillers for induction heating

Induction heating or welding can be performed by considering the combined effect of ferromagnetic heating due to magnetic hysteresis losses and eddy current heating due to conductive material. Nonconducting thermoplastic composite parts can be joined or welded by induction heating using a susceptor sheet filled with nickel-coated carbon fibers (NiCCFs) and nickel-coated graphite particles (NiCGPs) or both with polypropylene (PP) thermoplastic matrix. Above the percolation threshold, NiCCFs can serve as conductive materials and nickel coating will provide the ferromagnetic heating. NiCCF/PP and NiCCF/NiCGP/PP susceptor sheets were developed via melt mixing using a twin-screw extruder and sheets were produced by Calendering process. Induction heating tests were performed on a circular pancake coil and at frequencies below 1 MHz. In induction heating, fiber heating by Joule loss, junction heating (i.e. dielectric heating and contact resistance heating), as well as magnetic hysteresis effect were observed in both the cases. Heating in hybrid filler was higher at lower filler concentrations; however, with higher concentrations, heating reduced. Reduction in induction heating maybe due to a reduction in electrical conductivity was observed. Electrical conductivity was measured in fibers direction by a Keithley electrometer using a four-point measuring method and temperature was measured by an infrared thermal camera. Microstructure characterization was performed by X-ray computed microtomography and light microscopy.

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°C and slightly increased the TC of the X–Y basal plane of the GF/Cu composites with 20vol%–30vol% graphite flakes. However, when the graphite flake content was greater than 30vol%, 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.