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Triobological Behavior of Pickering Emulsions Stabilized with Alkylamine Edge-functionalized Graphene Oxide

期刊: CHINA SURFACE ENGINEERING, 2019; 32 (5)

In order to explore the potential application of graphene oxide (GO) in the field of metalworking fluid, GO was synthesized by improved Hummers' method, followed by edge-functionalization with n-octanylamine, and Pickering emulsions based on functionalized GO were constructed. The oil-water interfacial behaviors of functionalized GO at liquid-liquid interfaces, together with the tribological behaviors of GO-based Pickering emulsions at solid-liquid interfaces were respectively studied. The interfacial tension of functionalized GO at different oil-water interfaces was studied by full-automatic interfacial tension tester. And the interfacial lubricating properties of GO-based Pickering emulsions on CoCrMo alloy and 304 stainless steel were studied by UMT-tribolab and white light interferometer. To clarify the lubricating mechanism of GO-based Pickering emulsions, the composition of lubricating films on metal friction pairs was analyzed by Micro-Raman and XPS. The results show that the friction-reducing properties of GO-based Pickering emulsions are better than that of base emulsion, and alkylamine functionalized GO shows better lubrication performance on CoCrMo alloy than on that 304 stainless steel. Compared with base emulsion, when the friction counterpart is CoCrMo alloy, GO emulsion can reduce the average friction coefficient and the steel ball wear rate by 35.9% and 46.7% respectively, while Oct-N-GO emulsion can reduce the average friction coefficient (COF) and the wear rate of steel ball by 48.7% and 73.0% respectively. The mechanism analysis shows that the good interfacial wettability of functionalized GO enables its Pickering emulsion to form a better interfacial lubricating film on metal surfaces. The alkylamine chains at GO edges are more prone to be sheared during friction, which reduces the interfacial shear force and results in reducing friction. At the same time, the lubricating film formed by Oct-N-GO contains higher content of C-O-C/C-OH and C=O, which can adsorb or fill the metal surfaces and play an anti-wear role.

Preparation and Durability of Modified Epoxy Resin-based Nano-alumina Superhydrophobic Coating

期刊: CHINA SURFACE ENGINEERING, 2019; 32 (5)

With a wide potential application in many different fields, superhydrophobic surfaces have attracted much attention, while their surface structure can be easily damaged by environmental and mechanical effects and thereby causes superhydrophobic performance failure. To solve these practical problems, a robust superhydrophobic coating was fabricated with modified epoxy resin and oleophilic alumina NPs. Prepared by layered preparation method and air spraing method, the coating had a contact angle of 157.57 degrees and a sliding angle of 2 degrees. In terms of mechanical durability, the coating retained superhydrophobic properties after 30 times of sandpaper rubbing or 45 times tape peeling, exhibiting a better mechanical wear resistance than that of the commercial coatings ("Never-wet"). In terms of chemical durability, the coating still has good superhydrophobic property after being immersed in an acid or base solution for 100 min. It is concluded that superhydrophobic surfaces prepared by the materials system own good mechanical robustness.

Effects of Fuel Type and Spraying Parameters on Microstructure and Mechanical Properties of HVOF Sprayed WC10Co4Cr Coatings

期刊: CHINA SURFACE ENGINEERING, 2019; 32 (5)

HVOF sprayed WC-based cermet coatings have been widely used in industries for wear, corrosion and cavitation protection of the metallic components. WC10Co4Cr coatings were deposited by gas fuel-HVOF (GF-HVOF) and liquid fuel-HVOF (LF-HVOF) processes at 9 different spraying conditions to investigate the effect of fuel type on microstructure, residual stress and mechanical properties of HVOF cermet coatings. For the coatings prepared at optimized conditions, residual stress raised in the coatings was in-situ monitored by testing the curvature evolution of the substrate during spraying. Vickers microhardness, indentation and ball-on-disc wear test were performed to evaluate mechanical properties of the resultant cermet coatings. The results show that cermet particles have higher velocity and lower surface temperature in LF-HVOF than those in GF-HVOF. A compressive residual stress is formed in the LF-HVOF WC10Co4Cr coating while a residual stress is detected in the GF-HVOF coating. Because of combination of more compact microstructure and compressive residual stress, the LFHVOF cermet coating (1280 HV0.3, 7.3 MPa.m(0.5)) shows both higher hardness and higher fracture toughness and thereby higher wear resistance than that of CF-HVOF coating (1032 HV0.3, 4.5 MPa.m(0.)(5)).

Effects of Vibration Acceleration on Stress Deformation, Microstructures and Properties of Fe314 Alloy Fabricated by Plasma Additive Manufacturing

期刊: CHINA SURFACE ENGINEERING, 2019; 32 (5)

Vibration was applied during plasma surfacing welding of Fe314 self-fluxing alloy powder additive manufacturing process. The changes of microstructures, properties, stress and deformation of the formed parts subjecting to vibration were analyzed and compared by means of blind hole method, scanning electron microscope, tension test and so on. The results show that it is detrimental to the formation of thin-walled parts and fine structures after the vibration is applied, however, the residual deformation and residual stress of the formed sample are improved to some extent. When the vibration acceleration is 4 m/s(2) and 6 m/s(2), the residual stress and deformation can be obviously reduced. After vibration, the microstructure of the formed samples is significantly refined and the tensile properties are improved. When the vibration acceleration is 4 m/s(2), the dendrites are significantly refined and the comprehensive mechanical properties are distinctly improved.

Failure Behavior of Cobalt-based Plasma Cladding Layer in Thermal and Mechanical Conditions

期刊: CHINA SURFACE ENGINEERING, 2019; 32 (5)

Surface/interface structure is crucial to the service performance and safety reliability of mechanical parts. To study the failure behavior of surface/interface structure under the action of thermal and mechanical, cobalt-based cladding layer was prepared on FV520B substrate by plasma cladding technology, the surface/interface structure of the cladding layer was detected through thermal fatigue test, tensile test at normal/high temperature, and the microstructure was observed by a scanning electron microscope and a metallographic microscope. Results show that cobalt-based cladding layer has excellent thermal fatigue resistance at 600 degrees C, and the fatigue resistance of the surface/interface structure of cladding layer decreases with the increasing of temperature, and the fatigue crack originates in the interface between the coating and the substrate. The coating breaks in the uniaxial tensile experiment, and further studies show that the coarse dendrite are broken at the multilayer lap position. In high-temperature tensile experiment between 300 and 700 degrees C, the surface/interface structure of cobalt-based cladding layer failes inner the coating at various temperatures, while the failure position transferres from the coating to the substrate as the strength of the cladding layer increased with the addition of alloy elements.

Phase Structure and Tribological Properties of DLC Coatings Combined with Nitriding on Surface of AISI 316L

期刊: CHINA SURFACE ENGINEERING, 2019; 32 (5)

In order to improve the adhesion strength between diamond-like carbon (DLC) coatings and the austenitic stainless steels, DLC coatings were prepared on the surface of untreated and nitridied AISI 316L at different deposition temperatures by plasma-enhanced chemical vapor deposition (PECVD) technology. Phase structure and tribological properties of the coating were investigated. X-ray diffraction (XRD) and Raman spectroscopy were used to characterize the phase structure of the coatings. The cross-sectional morphology was observed by scanning electron microscope (SEM), and the depth distribution of nitrogen and carbon elements was measured by EDS. Nano-indentation instrument, friction and wear tester, 3D optical microscope and scratch tester were used to evaluate the tribological properties of DLC coatings. The results show that the adhesion strength and wear resistance of DLC coatings combined with nitriding are higher than that of the single DLC coatings. Deposited at 100 degrees C, accompanied by the best modification, the hardness and adhesion strength increases by 25% and 175%, respectively, and the comprehensive performance is the best. During the deposition of DLC coatings, the nitrogen atoms in the nitrided layer are re-distributed due to the diffusion, increasing the thickness of the nitrided layer and decreasing the gradient of hardness, which contributes to a better transition between the substrate and the DLC coatings.

Corrosion Resistance of PPy/rGO Composite Coating on Aluminum Alloy for Aircraft Structure

期刊: CHINA SURFACE ENGINEERING, 2019; 32 (5)

To study the corrosion resistance of the composite coating between GO and polypyrrole, a polypyrrole (PPy) coating was prepared by electrochemical polypyrrole monomer on Al sheet through potentiostatic method. The polypyrrole/reduced graphene oxide (PPy/rGO) composite coating was then formed by electroplating graphene oxide solution on the surface of the PPy coating. SEM, Raman and FTIR were used to characterize the microstructure and composition of the coating. Hydrophobicity of the coating was tested by using the contact angle measuring instrument. The corrosion resistance of the coating was analyzed by polarization curve and EIS. The results show that the rGO coating covers the defects on the surface of the PPy coating, which makes the surface of composite coating level and smooth. PPy/rGO composite coating shows good hydrophobicity than the PPy coating. The corrosion current density of the PPy/rGO composite coating is smaller than that of the PPy coating and Al, indicating that the corrosion rate is lower. Compared with the PPy coating and Al, PPy/rGO composite coating has larger impedance arc, which indicates the PPy/rGO composite coating has stronger hindrance to electrolyte ion in solution. Al and PPy coatings are corroded to different degrees, however, the PPy/rGO composite coatings has no obvious corrosion Phenomenon. Therefore, the PPy/rGO composite coating has better corrosion resistance.

Influence of Hydrostatic Pressure on Corrosion Behavior of Cerium Conversion Coating on X80

期刊: CHINA SURFACE ENGINEERING, 2019; 32 (5)

Cerium conversion coating as an environmentally friendly conversion film can improve the corrosion resistance of materials. Cerium conversion coating was prepared on X80 by electrochemical deposition, and the corrosion behavior of the coating on X80 in 0.1 MPa and 20 MPa hydrostatic pressure 3.5% NaCl solution was studied. Open circuit potential, electrochemical impedance spectroscopy, linear polarization resistance and polarization curve were carried out by high temperature and high pressure online electrochemical testing autoclave. Scanning electron microscopy, energy disperse spectroscopy and contact angle meter were used to analyze the topography, elements and hydrophilicity of the surface before and after corrosion. Results show that the cerium conversion coating can significantly improve the electrochemical properties of X80 in shallow sea with a hydrostatic pressure of 0.1 MPa, while open circuit potential, linear polarization resistance and electrochemical impedance spectroscopy of cerium conversion coating on X80 obviously decline and corrosion current density increases in deep sea with a hydrostatic pressure of 20 MPa. Cerium conversion coating on X80 has much cracks after corrosion in deep sea with a hydrostatic pressure of 20 MPa, while no obvious defects is found in shallow sea with a hydrostatic pressure of 0.1 MPa. Cerium conversion coating shows hydrophilicity before corrosion, while contact angle increases after corrosion, showing hydrophobicity.

Effects of Icariin Contents on Properties of Mg/UMAO/CS/IC Coating

期刊: CHINA SURFACE ENGINEERING, 2019; 32 (5)

To study the effects of icariin contents on the characteristics of magnesium/ultrasonic micro-arc oxidation/chitosan/icariin (Mg/UMAO/CS/IC), and enhance the corrosion resistance of pure magnesium, Mg/UMAO/CS/IC coating was prepared using a combined method of UMAO with electrophoretic deposition (EPD) technique on the Mg substrate. The coatings were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), atomic force microscopy (AFM) and Fourier transform infrared (FTIR) spectroscopy. Corrosion resistance was investigated by electrochemical impedance spectroscopy and potentiodynamic polarization in a simulated body fluid (SBF) solution. The results show that the UMAO coating is well sealed by CS/IC coating with a content of 0.4 g/L IC. The coatings with various IC contents all consists of Mg, MgO, CS and Mg2SiO4 phase. The corrosion current density of the coatings with various IC contents are at least one order of magnitude lower compared with that of Mg substrate, which implies that it can provide a more effective protection for Mg substrate. With a content of 0.4 g/L IC, the Mg/UMAO/CS/IC coating has the best corrosion resistance, evidenced by the minimum corrosion current density (1.667x10(-6) A/cm(2)). Mg/UMAO/CS/IC coating effectively solves the problem of high corrosion rate of Mg in clinical bone fixation applications.

Corrosion Resistance and High-temperature Oxidation Behavior of Micro-arc Oxidation Ceramic Coating on High Niobium gamma-TiAl Alloy

期刊: CHINA SURFACE ENGINEERING, 2019; 32 (5)

The micro-arc oxidation (MAO) technique was used to prepare in-situ ceramic coating on the surface of high niobium gamma-TiAl alloy in sodium silicate and potassium hydroxide solution to improve the high-temperature oxidation resistance. The SEM, XRD, XPS, electrochemical workstation and box-type resistance furnace high-temperature oxidation test were used to analyze the surface and cross section morphologies, phase composition, elemental chemical bonding state, corrosion resistance and high-temperature oxidation behavior of the coating, respectively. The results of XRD and XPS show that the ceramic coating is mainly composed of Al2TiO5, SiO2 and Nb2O5. The coating has a good interface with the substrate, with a thickness of 2.15 mu m. After micro-arc oxidation treatment, the corrosion resistance of high niobium gamma-TiAl alloy in 3.5% NaCl solution is improved by nearly one order of magnitude. The oxidation weight gain of the coated sample at 800-900 degrees C is only 8.9%-37.5%. The oxidative activation energy of the uncoated sample increases from 247.79 kJ/mol to 574.41 kJ/mol for the coated sample due to the formation of the MAO coating.

Numerical Simulation and Experiment Micro-dimple Array on E690 High-strength Steel Surface Induced by Laser Shock Processing

期刊: CHINA SURFACE ENGINEERING, 2019; 32 (5)

To study how different times of laser shocks affect the micro-dimple, surface residual stress and microstructure of E690 high-strength steel, the finite element software ABAQUS was used to simulate the surface evolution process of the sample. E690 high-strength steel specimens were impacted by pulsed laser with a power density of 7.96 GW/cm(2). Three-dimensional surface morphology was measured by an optical profiler. The surface residual stress and FWHM values of laser-shocked zone were measured by an X-ray diffraction residual stress tester, and the microstructure and morphology of the impacted area were characterzal by using TEM. Results show that when pulse laser with a power density of 7.96 GW/cm(2) impacts 1-4 times, the resultant depths present an increasing trend between 10 and 40 am. A comparison of the simulated and measured results of three-dimensional surface topography in depth-wise direction suggests that the error rate falls within a reasonable range. When pulse laser impacts 2 times and more, test values of residual compressive stress of the specimens tend to be consistent in all directions. FWHM values gradually increase and tended to be equal with the impact being performed 4 and 3 times. TEM images and electron diffraction patterns of specimens that has been impacted by pulse laser for 2 times show nanocrystals forming on the surface of the micro-dimple.

Research Progress in Spectroscopic Diagnosis of Plasma Jet Characteristics Under PS-PVD

期刊: CHINA SURFACE ENGINEERING, 2019; 32 (5)

Plasma spray-physical vapor deposition (PS-PVD), as a new spray technology, combines the advantages of both vapor deposition and thermal spray processes. The plasma characteristics determine the micro structure and properties of the coatings. As a plasma jet characteristic diagnosis technology, optical emission spectroscopy (OES) can realize the in-situ detection of jet characteristics, which is a powerful means to judge the evaporation phenomenon in the jet. This paper introduced the changes of jet characteristics before and after the powder was inject and after the jet impacted the substrate. It shows the calculation of the state of each particle in the jet under the assumption of local thermodynamic equilibrium (LTE) and the theory of broadening, and explores the activities of mass and heat transfer in different regions of the jet. Ar/He has the highest temperature, and Ar has a high enthalpy value, which plays a major role in evaporating the powder. The He condensed jet energy plays a key role in the heating and evaporation of the powder. H2 expands the jet width and reduces the jet temperature to form a mixed layer with dense and columnar structure. Combined with simulation calcnlation and spectroscopy of the jet, it is known that the complex thermal interaction in the spray gun is the main reason for powder heating. The thermal energy and kinetic energy are alternately converted in the expansion/compression zone at the nozzle, and the middle and rear sections of the jet continue to vaporize due to low pressure and high temperature. After reaching the peak, the jet is in the stage of condensation and cooling, and some of the vapor phase atoms are agglomerated into cluster-like particles. The effects of power, current and powder feeding rate on plasma jet characteristics are also summarized.

Functional Surface and Its Device Based on Flouresence Hydrogel

期刊: CHINA SURFACE ENGINEERING, 2019; 32 (5)

There are many functional applications based on hydrogel material, including tissue engineering, energy storage, and flexible devices. The main structure was constructed by polyvinyl alcohol, chitosan and agarose. Hydroxyethyl cellulose was added to enhance plasticity and maintain moisture. Carbon quantum dots were added to bring fluorescent property. The multi-network hydrogel had excellent self-healing properties and excellent tensile strength up to 33 MPa and the self-healing could take place quickly in a variety of media. The self-healing efficiency in air reached up to 93% in just 60 s. The result show that the fluorescence intensity of the hydrogel is negatively correlated with the pressure on the surface, and is positively correlated with its tensile elongation. The data fitting confirmation that the tensile elongation can be monitored by detecting the fluorescence intensity of the hydrogel, and combine composite hydrogel with gecko-like structure to form a pressure detector that can adhere to various surfaces. The liquid pressure is confirmed to be monitored by detecting the fluorescence intensity of the device. This research expands the application of fluorescent hydrogel materials and expects to be used for pressure detection under liquid and engineering structure failure monitoring.

Electrical Property and Biocompatibility of Polyvinylidene Fluoride Films Modified by Polypyrrole

期刊: CHINA SURFACE ENGINEERING, 2019; 32 (5)

Polyvinylidene fluoride (PVDF) has attracted much attention due to its biocompatibility, piezoelectric and favourable mechanical properties. The modification of polypyrrole coating on the surface of the PVDF film by electrochemical method was studied. The surface morphology of the nanostructured polypyrrole coating modified PVDF film was observed by scanning electron microscopy (SEM) and atomic force microscope (AFM). The surface contact angle analyzer and AFM were used to study the hydrophilicity and electrical properties of the PVDF membrane modified by the nano structure polypyrrole coating. The biocompatibility of the nanostructured polypyrrole coating modified PVDF membrane was investigated by in vitro mineralization, cell viability staining and CCK-8 assay, respectively. The results show that the surface hydrophilicity, surface potential distribution and biocompatibility of PVDF films are significantly improved by the modification of the nanostructured polypyrrole coating, and more conducive to the surface bone mineral deposition and cell adhesion and proliferation. In addition, the PVDF membrane modified by polypyrrole nanowire has higher hydrophilicity and surface potential distribution, which is more conducive to cell adhesion and proliferation.

Preparation of PDA/TiO2 Composite Film on PTFE and Its Cellular Response

期刊: CHINA SURFACE ENGINEERING, 2019; 32 (5)

Polytetrafluoroethylene (PTFE) has been widely applied as a biomaterial owing to its good stability and bioinertness. A PDA/TiO2 composite film was prepared on the surface of PTFE substrate through polydopamine (PDA) assisted in-situ co-deposition, so that the hydrophilicity and cellular responses could be improved. It was found that the film consists of PDA and TiO2. The content of TiO2 in the film can be controlled through the amount of TiO2 sol added in the deposition solution. The film is bonded to the substrate strongly. The shear strength reaches 23.5 MPa. Fibroblasts and osteoblasts are seeded on the surface of the modified substrate, and one-day cell adhesion and three-day proliferation experiments show that the cellular response of the modified substrate are significantly improved. Such deposition method is simple and easy, exhibiting wide potential in surface modification of PTFE for biomedical application.

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