Properties of polydimethylsiloxane hydrophobic modified duplex microarc oxidation/diamond-like carbon coatings on AZ31B Mg alloy

A reliable,high-performance coating procedure was developed using PDMS to modify a duplex MAO/DLC coating on an AZ31B Mg alloy.First,the duplex MAO/DLC coating was fabricated via a combined MAO and unbalanced magnetron sputter process.Subsequently,a PDMS solution was used to modify the MAO/DLC coating via a conventional dip-coating method.The surface characteristics,bond strength,hardness,tribological behaviour,and corrosion resistance of the coated samples were evaluated via SEM,CA,Raman spectroscopy,friction and wear behaviour,polarisation curve,and NSS tests.The PDMS modification reduced the HIT of MAO/DLC coating from 15.96 to 8.34GPa;this is ascribed to the penetration of PDMS,which has good rheological properties to form a viscoelastic Si-based organic polymer layer on the MAO/DLC coating.However,the PDMS-modified MAO/DLC coating was denser,hydrophobic,and had higher bond strength compared with MAO-and MAO/DLC-coated samples.Moreover,the PDMS modification reduced the COF and wear rate of the duplex MAO/DLC coating.This indicates that the PDMS improved the tribological behaviour owing to the transferred Si oxide that originated from the Si-O network of the PDMS,as well as the low graphitisation of the DLC layer during sliding.Furthermore,the corrosion current density of the MAO/DLC-coated sample modified by PDMS for 10min decreased by two order of magnitude compared with that of the MAO/DLC-coated sample but by five orders of magnitude compared with that of the bare substrate.The NSS tests proved that the PDMS layer slowed the corrosion of the Mg alloy under long-term service,enhancing the corrosion protection efficiency.The results are attributed to the high bond strength and lubricant MAO/DLC layer,and the dual role of sealing and hydrophobicity of PDMS.Therefore,PDMS modification is promising for the fabrication of protective materials for Mg alloys that require corrosion and wear resistance.

Deposition behavior and tribological properties of diamond-like carbon coatings on stainless steels via chemical vapor deposition

A systematic investigation was carried out to observe the deposition rate of a diamond-like carbon(DLC) coating on two stainless steel substrates by chemical vapor deposition(CVD). The objective of this research is to study the deposition behavior of the DLC coating and its tribological properties in different combinations of methane(CH_4) and nitrogen, which were used as precursor gases. The results reveal that the deposition rate increases with increasing CH_4 content up to 50 vol%. The hardness of the DLC-deposited layer also increases while the friction coefficient decreases with increasing CH_4 gas content up to 50% in the precursor gas mixture.

Synergistic tribological effect between polyisobutylene succinimide-modified molybdenum oxide nanoparticle and zinc dialkyldithiophosphate for reducing friction and wear of diamond-like carbon coating under boundary lubrication

Organic molybdenum lubricant additive like molybdenum dialkyl dithiocarbamate(MoDTC)can cause wear acceleration of diamond-like carbon(DLC)coating coupled with steel under boundary lubrication,which hinders its industrial application.Therefore,polyisobutylene succinimide(PIBS),an organo molybdenum amide,was adopted to modify molybdenum oxide affording molybdenum polyisobutylene succinimidemolybdenum oxide nanoparticles(MPIBS-MONPs)with potential to prevent the wear acceleration of DLC coating.The thermal stability of MPIBS-MONPs was evaluated by thermogravimetric analysis.Their tribological properties as the additives in di-isooctyl sebacate(DIOS)were evaluated with MoDTC as a control;and their tribomechanism was investigated in relation to their tribochemical reactions and synergistic tribological effect with zinc dialkyldithiophosphate(ZDDP)as well as worn surface characterizations.Findings indicate that MPIBS-MONPs/ZDDP added in DIOS can significantly reduce the friction and wear of DLC coating,being much superior to MoDTC.This is because MPIBS-MONPs and ZDDP jointly take part in tribochemical reactions to form a composite tribofilm that can increase the wear resistance of DLC coating.Namely,the molybdenum amide on MPIBS-MONPs surface can react with ZDDP to form MoS2 film with excellent friction-reducing ability;and MPIBS-MONPs can release molybdenum oxide nanoparticle to form deposited lubrication layer on worn surfaces.The as-formed composite tribofilm consisting of molybdenum oxide nanocrystal,amorphous polyphosphate,and molybdenum disulfide as well as a small amount of Mo2C accounts for the increase in the wear resistance of DLC coating under boundary lubrication.

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.

Tribological performance of hydrogenated diamond-like carbon coating deposited on superelastic 60NiTi alloy for aviation selflubricating spherical plain bearings

It is imperative to develop a novel matching of metallic substrate and self-lubricating coating for aircraft spherical plain bearing in a wide range of service conditions.As a new type of superelastic material,60NiTi alloy meets the performance requirements of aerospace bearing materials,but exhibits poor tribological performance,especially under the conditions of dry sliding friction.A Hydrogenated Diamond-Like Carbon(H-DLC)coating was deposited on the 60NiTi alloy to improve its tribological performance.The microstructure and mechanical behavior of the 60NiTi alloy and its H-DLC coating were explored.Results show that improvement of friction and wear performance of the H-DLC coating deposited on the 60NiTi substrate is mainly achieved by graphitization at the friction interface and the transfer film produced on the counterpart ball.The increased friction load leads to intensification of graphitization at the friction interface and formation of continuous and compact transfer film on the surface of the counterpart ball.

The friction of diamond-like carbon coatings in a water environment

Diamond-like carbon(DLC)coatings are known to provide beneficial mechanical and tribological properties in harsh environments.Their combination of high wear resistance and low friction has led to their extensive use in any number of industries.The tribological performance of a DLC coating is varied however,and the frictional response is known to be strongly dependent on the surrounding environment,as well as the material composition and bonding structure of the DLC coating.This paper presents an up-to-date review on the friction of DLC coatings in a water environment,with a special focus on transfer layer formation and tribochemistry.

Structure and Performance of TiC-containing Diamond-like Carbon Nanocomposite Coatings Deposited by Rectangular Cathodic Arc Ion-plating

TiC-containing diamond-like carbon （TiC-DLC） nanocomposite coatings were deposited by a rectangular cathodic arc ion-plating system using C2H2 as reacting gas. Raman spectroscopy and transmission electron microscopy analysis show that with increasing flow rate of C2H2, the structure of nanocomposite coatings changes from TiC nanograin-containing to graphite nanograin-containing DLC. The harness measurements show that the hardness decreases from 28 GPa to 18 GPa with increasing C2H2 flow rate. The scratch test show that a high critical load （〉40 N） was obtained and exhibited a good adhesion between the coating and the substrate. Wear experiment shows that the friction coefficient of TiC-DLC nanocomposite coatings decreases with increasing C2H2. A low friction coefficient of 0.07 was obtained at 480 sccm C2H2.

Heat Resistant Properties of Some Elements-Incorporated Diamond-Like Carbon Films and Their Trial Applications for Micro End Mill Coatings

In this article, the results obtained from a study carried out on the some elements-incorporated diamond-like carbon (DLC) films are reported. All the films were deposited using plasma-based ion implantation (PBII) technique. The deposited films were annealed at 400℃, 650℃ and 900℃ in an air atmosphere for 1 hour. The effects of adding hydrogen, silicon/oxygen and silicon/nitrogen into the DLC film on chemical composition, friction coefficient and corrosion resistance were investigated. The films coated micro end mills performance was also assessed. The results indicate that all the films showed almost constant atomic contents of C, Si, O and N until annealing at 400℃. However, the films were completely destroyed at 650℃ with the increased Si and O contents, while the C content decreased. The incorporation of silicon/oxygen and silicon/nitrogen into the DLC exhibited lower values of friction coefficients than the hydrogenated DLC (DLC and H-DLC) before and after annealing at 400℃, whereas all the films presented the same values of friction coefficients after annealing at 650℃ due to the completely destroy of the films. Furthermore, the incorporation of silicon/nitrogen into the DLC also exhibited better corrosion resistance and unbroken micro end mills performance on their surfaces. Thus, the incorporation of silicon/nitrogen into the DLC film can be considered beneficial in improving the micro end mills performance.

Enhanced corrosion resistance of epoxy resin coating via addition of CeO_(2) and benzotriazole

The use of fillers to enhance the corrosion protection of epoxy resins has been widely applied.In this work,cerium dioxide(CeO_(2))and benzotriazole(BTA)were introduced into an epoxy resin to enhance the corrosion resistance of Q235 carbon steel.Scanning electron microscopy results indicated that the CeO_(2) grains were rod-like and ellipsoidal in shape,and the distribution pattern of BTA was analyzed by energy dispersive spectroscope.The dynamic potential polarization curve proved the excellent corrosion resistance of the composite epoxy resin with CeO_(2) and BTA co-addition,and electrochemical impedance spectroscopy test analysis indicated the significantly enhanced long-term corrosion protection performance of the composite coating.And the optimal protective performance was provided by the coating containing 0.3%(mass)CeO_(2) and 20%(mass)BTA,which was attributed to the barrier performance of CeO_(2) particles and the chemical barrier effect of BTA.The formation of corrosion products was analyzed using X-ray diffraction.In addition,the corrosion resistance mechanism of the coating was also discussed in detail.

CoS Nanosheets Coated with Dopamine-Derived Carbon Standing on Carbon Fiber Cloth as Binder-Free Anode for Li-ion Batteries

Cobalt sulphides attract much attention as anode materials for Li-ion batteries(LIBs).However,its poor conductivity,low initial column efficiency and large volume changes during cycling have hindered its further development.Herein,novel interlaced CoS nanosheets were firstly prepared on Carbon Fiber Cloth(CFC)by two hydrothermal reactions followed with carbon coating via carbonizing dopamine(CoS NS@C/CFC).As a freestanding anode,the nanosheet structure of CoS not only accommodates the volume variation,but also provides a large interface area to proceed the charge transfer reaction.In addition,CFC works as both a three-dimensional skeleton and an active substance which can further improve the areal capacity of the resulting electrode.Furthermore,the coated carbon combined with the CFC work as a 3D conductive network to facilitate the electron conduction.The obtained CoS NS@C/CFC,and the contrast sample prepared with the same procedure but without carbon coating(CoS NS/CFC),are characterized with XRD,SEM,TEM,XPS and electrochemical measurements.The results show that the CoS NS@C/CFC possesses much improved electrochemical performance due to the synergistic effect of nanosheet CoS,the coated carbon and the CFC substrate,exhibiting high initial columbic efficiency(~87%),high areal capacity(2.5 at 0.15 mA cm−2),excellent rate performance(1.6 at 2.73 mA cm−2)and improved cycle stability(87.5%capacity retention after 300 cycles).This work may provide a new route to explore freestanding anodes with high areal specific capacity for LIBs.

Color and Gloss Changes of a Lignin-Based Polyurethane Coating under Accelerated Weathering

The purpose of this research study was to investigate the properties of polyurethane coatings based on lignin nano-particles.For this purpose,the prepared coatings were applied to pine wood surfaces and weathered artificially.Subsequently,color and gloss of the coatings were measured before and after the weathering test.Field emission scanning electron microscopy(FE-SEM)micrographs prepared from the coatings showed that the average size of nano-particles in the polyurethane substrate was approximately 500 nm.Nuclear magnetic resonance(13C-NMR)spectroscopy showed that strong urethane bonds were formed in the nano-lignin-based polyurethane.Differential calorimetric analysis(DSC)test revealed that the glass-transition temperature(Tg)of lignin nanoparticles modified with diethylenetriamine(DETA)was 112.8℃ and Tg of lignin nano-particles modified with ethylenediamine(EDA)was 102.5℃,which is lower than the Tg of un-modified lignin(114.6℃)and lignin modified with DETA(126.8℃)and lignin modified with EDA(131.3℃).The coatings modified with lignin nano-particles had a greater change in gloss.The lignin nano-particles in the modified coating are trapping hydroxyl radicals which reduces photoactivity and yellowing of the polyurethane by about 3 times compared to unmodified polyurethane coatings.After weathering test,the nano-lignin-based coating had a rougher surface with a lower contact angle(0.78°)compared to the unmodified polyurethane coating(0.85°).

Bonding characteristics of the Al_2O_3-metal composite coating fabricated onto carbon steel by combustion synthesis

The fabrication of an alumina-metal composite coating onto a carbon steel substrate by using a self-propagating high-temperature synthesis technique was demonstrated. The effects of the type and thickness of the pre-coated layer on the binding structure and surface qual- ity of the coating were systematically investigated. The macrostructure, phase composition, and bonding interface between the coating and the substrate were investigated by scanning electronic microscopy （SEM）, X-ray diffraction （XRD）, and energy-dispersive X-ray spectrometry （EDS）. The diffraction patterns indicated that the coating essentially consisted of α-Al2O3, Fe（Cr）, and FeO-Al2O3. With an increase in the thickness of the pre-coated working layer, the coating became more smooth and compact. The transition layer played an important role in enhancing the binding between the coating and the substmte. When the pre-coated working layer was 10 mm and the pre-coated transition layer was 1 ram, a compact structure and metallurgical bonding with the substrate were obtained. Thermal shock test results indicated that the ceramic coating exhibited good thermal shock resistance when the sample was rapidly quenched from 800℃ to room temperature by plunging into water.

SiC-Si-ZrSiO_4 Multiphase Oxidation Protective Coating for Carbon/Carbon Composites

In order to improve the anti-oxidation property of carbon/carbon （C/C） composites, a novel SiC-Si-ZrSiO4 multiphase oxidation protective coating was produced on the surface of C/SiC coated carbon/carbon compo ites by a pack cementation technique. The phase composition and microstructure of the as-prepared coatings were characterized by XRD （X-ray diffraction）, SEM （scanning electron microscopy） and EDS （energy dispersive spectroscopy）. Oxidation behavior of the multiphase coated C/C composites was also investigated. It showed that the as-prepared coating characterized by excellent oxidation resistance and thermal shock re- sistance could effectively protect C/C composites from oxidation at 1773 K for 57 h in air and endure the thermal cycle between 1773 K and room temperature for 12 times, whereas the corresponding weight loss is only 1.47%. The excellent oxidation protective ability of the SiC-Si-ZrSiO4 coating could be attributed to the C/SiC gradient inner layer and the multiphase microstructure of the coating.

Effects of heat treatment on the corrosion resistance of carbon steel coated with LaMgAl_(11)O_(19) thermal barrier coatings

LaMgAl11O19thermal barrier coatings（TBCs） were applied to carbon steels with a NiCoCrAlY bond coat by plasma spraying. The effects of heat treatment on the corrosion resistance of carbon steel coated with LaMgAl11O19TBCs were investigated in 3.5wt% Na Cl solution using polarization curves, electrochemical impedance spectroscopy（EIS）, scanning electron microscopy（SEM）, and X-ray diffraction（XRD）. The results show that a large number of cracks are found in the LaMgAl11O19TBCs after the samples are heat-treated, including some through-thickness cracks. The corrosion forms of the as-sprayed and heat-treated TBCs are uniform corrosion and pitting corrosion, respectively. The as-sprayed TBCs exhibit three EIS time constants after being immersed for less than 7 d, and then a new time constant appears because of steel substrate corrosion. When the immersion time is increased to 56 d, a Warburg impedance（W） component appears in the EIS data. The EIS data for the heat-treated TBCs exhibit only two time constants after the samples are immersed for less than 14 d, and a new time constant appears when the immersion time is increased further. The heat treatment reduces the corrosion resistance of carbon steel coated with LaMgAl11O19TBCs. The corrosion products are primarily γ-Fe OOH and Fe3O4.

Coating Carbon Nanotubes with Europium Oxide

Carbon nanotubes (CNTS) coating with europium oxide by a simple method is reported in this letter for the first time. The CNTS were refluxed in a solution of nitric acid containing europium nitrate, and the pH value was subsequently ajusted with ammonia solution. At last, the mixture was filtered and annealed. The TEM micrograph showed that the CNTS were covered with a uniform thin layer with thickness of about 15 nm. The XRD results revealed that the CNTS were coated with europium oxide.

Si-Al-Ir Oxidation Resistant Coating for Carbon/Carbon Composites by Slurry Dipping

A Si-Al-lr oxidation resistant coating was prepared for SiC coated carbon/carbon composites by slurry dipping. The phase composition, microstructure and oxidation resistance of the as-prepared Si-Al-lr coating were studied by XRD （X-ray diffraction）, SEM （scanning electron microscopy）, and isothermal oxidation test at 1773 K in air, respectively. The surface of the as-prepared Si-Al-lr coating was dense and the thickness was approximately 100 um. Its anti-oxidation property was superior to that of the inner SiC coating. The weight loss of SiC/Si- Al-lr coated carbon/carbon composites was less than 5 wt. pct after oxidation at 1773 K in air for 79 h. The local oxidation defects in the coating may result in the failure of the SiC/Si-Al-Ir coating.

Corrosion protection investigations of carbon dots and polydopamine composite coating on magnesium alloy

A composite coating of nitrogen-doped carbon dots(N–CDs)and polydopamine(PDA)was prepared on magnesium alloy by combining electrodeposition with dip coating methods.The microstructure of the N–CDs/PDA composite coating,including composition,surface morphology,and crystalline structure,is characterized by Raman spectroscopy,scanning electron microscopy,transmission electron microscopy,and X-ray photoelectron spectroscopy,respectively.The corrosion protection performances of the composite coating are evaluated by potentiodynamic polarization tests,electrochemical impedance spectroscopy,and salt spray tests.The effect of the particle size of the N–CDs on the corrosion performance is also investigated.The results show that the corrosion performance of the N–CDs coatings are enhanced with the increase of the particle sizes.Furthermore,an obvious self-healing performance is observed on the surface of the N–CDs/PDA composite coating.These results indicate that N–CDs/PDA composite coating can improve the corrosion performance of the Mg alloy,and open a new design direction for the protective coating of metallic materials.

Preparation of Diamond-like Carbon Films on the Surface of Ti Alloy by Electro-deposition

In this paper, diamond-like carbon (DLC) films were deposited on Ti alloy by electro-deposition. DLC films were brown andcomposed of the compact grains whose diameter was about 400 nm. Examined by XPS, the main composition of the filmswas carbon. In the Raman spectrum, there were a broad peak at 1350 cm^(-1) and a broad peak at 1600 cm^(-1), which indicatedthat the films were DLC films.

Influence of carbon sources on the performance of carbon-coated nano-silicon

Silicon-based material is an important anode material for next-generation lithium-ion batteries.In order to overcome its shortcomings,carbon coating is often employed to improve the electrochemical performance.However,the carbon source,carbon content,and different contact and mixing schemes between carbon sources and silicon are all complex factors and need to be clarified.In this study,nano-silicon is coated by the chemical vapor deposition method using different carbon sources,such as acetylene,methane,propane,and propylene.Carbon content after coating is designed to stay at the same level to reduce the experimental error.Results show the sample with higher conductivity provides higher cycle performance.Propylene is the best choice of the four carbon sources studied in this work.These results indicate that the selection of the carbon source is an important factor that plays a significant role in electrochemical performance.

Carbon-coated ZnO Nanocomposite Microspheres as Anode Materials for Lithium-ion Batteries

The carbon-coated ZnO nanospheres materials have been synthesized via a simple hydrothermal method.The effect of carbon content on the microstructure,morphology and electrochemical performance of the materials was investigated by XRD,Raman spectroscopy,transmission electron microscopy,scanning electron microscopy and electrochemical techniques.Research results show that the spherical ZnO/C material with a carbon cladding content of 10%is very homogeneous and approximately 200 nm in size.The electrochemical performances of the ZnO/C nanospheres as an anode materials are examines.The ZnO/C exhibits better stability than pure ZnO,excellent lithium storage properties as well as improved circulation performance.The Coulomb efficiency of the ZnO/C with 10%carbon coated content reaches 98%.The improvement of electrochemical performance can be attributed to the carbon layer on the ZnO surface.The large volume change of ZnO during the charge-discharge process can be effectively relieved.