Effect of spraying power on microstructure and bonding strength of MoSi2-based coatings prepared by supersonic plasma spraying

MoSi₂-based oxidation protective coatings for SiC-coated carbon/carbon composites were prepared using a supersonic plasma spraying at the power of 40 kW, 45 kW, 50 kW and 55 kW, respectively. Effect of spraying power on the microstructure and bonding strength of MoSi₂-based coatings was studied. The results show that coatings become more and more compact and the bonding strength increases when the spraying power increases from 40 kW to 50 kW. At the power of 50 kW, the coatings were dense and the bonding strength reached a maximum value of 14.5 MPa. As the spraying power is of sufficient magnitude, many cracks and pores reappaer in coatings and the bonding strength between coating and substrate also decreases.     

树脂基复合材料在连续激光作用下的损伤

 采用热压工艺制备了碳纤维布和高硅氧纤维布增强的环氧树脂和酚醛树脂基复合材料,研究了不同功率密度连续激光辐照下,复合材料的破坏形式及其组织结构与力学性能的变化。结果表明：当激光辐照功率密度大于0.1 kW/cm²后,树脂基体产生燃烧,碳纤维没有明显的损伤,而玻璃纤维布开始熔融,复合材料的拉伸性能降低30%~40%;当功率密度达到1 kW/cm²以后,除基体燃烧外,碳纤维复合材料产生明显的鼓泡分层,表层碳纤维有少量破断,而高硅氧纤维产生明显的熔融烧损,复合材料的拉伸性能降低80%以上。采用有限元计算方法,对碳纤维增强环氧树脂复合材料在连续激光辐照下的温度场进行了研究,计算结果与实验中复合材料的损伤行为相吻合。     

Electrochemically assisted co-deposition of calcium phosphate/collagen coatings on carbon/carbon composites

Calcium phosphate (CaP)/collagen coatings were prepared on the surface of carbon/carbon (C/C) composites by electrochemically assisted co-deposition technique. The effects of collagen concentration in the electrolyte on morphology, structure and composition of the coatings were systematically investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transformed infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The adhesive strength of the coatings was also evaluated by scratch tests and tensile bond tests. It was demonstrated that the coatings of three-dimensional collagen network structure was formed on the C/C composites from the electrolyte containing collagen. The surface of the collagen network was covered by uniform CaP aggregates. The coatings were actually composites of CaP and collagen. Hydroxyapatite (HA) was a favorable composition in the coatings with the increase of the collagen concentration in the electrolyte. The formed collagen network increased the cohesive and adhesive strength of the coatings. The adhesive strength between the coatings and substrates increased as the collagen concentration in the electrolyte increased. The coatings prepared at the collagen concentration of 500 mg/L in the electrolyte were not scraped off until the applied load reached 32.0 ± 2.2 N and the average tensile adhesive strength of the coatings was 4.83 ± 0.71 MPa. After C/C coated with composite coatings (500 mg/L) being immersed in a 10⁻³ M Ca (OH)₂ solution at 30-33 °C for 96 h, nano-structured HA/collagen coatings similar to the natural human bone were obtained on the C/C.     

Influence of interfacial reaction on interfacial performance of carbon fiber and polyarylacetylene resin composites

The influence of interfacial reaction on interfacial performance of carbon fiber/polyarylacetylene resin composites was studied. For this purpose, vinyltrimethoxysilane containing a double bond was grafted onto the carbon fiber surface to react with the triple bond of polyarylacetylene resin. The reaction between polyarylacetylene resin and vinyltrimethoxysilane was proved by reference to the model reaction between phenylacetylene and vinyltrimethoxysilane. Surface chemical analysis by XPS, surface energy determination from the dynamic contact angle, and the interfacial adhesion in composites was evaluated by interfacial shear strength test as well. It was found that vinyltrimethoxysilane, which can react with polyarylacetylene resin, had been grafted onto the carbon fiber surface. Furthermore, because the reaction between polyarylacetylene resin and vinyltrimethoxysilane took place at the interface, the interfacial adhesion in composites was significantly increased, and the improvement of interfacial adhesion was all attributed to the interfacial reaction.     

Wear Performance and Mechanisms of Polyphenylene Sulfide/Polytetrafluoroethylene Wax Composite Coatings Reinforced by Graphene

Polyphenylene sulfide (PPS) composite coatings reinforced by graphene were prepared through a spraying method. Wear performance of the composite coatings were evaluated using a block-on-ring test rig, and the results showed that the wear life of the composite coatings were over seven times higher than that of a pure PPS coating. Wear mechanisms of PPS composite coatings reinforced by graphene are discussed. It was concluded that adhesive wear was the major wear mechanism of the pure PPS coating but the wear form of the composite coatings was dominated by abrasive wear due to the graphene filler that has high mechanical strength. In addition, fatigue wear appeared for composite coatings with higher content of graphene. The formation of a uniform thin transfer film on the counterpart ring and fine wear debris for the composites coatings during abrasion were consistent with the improvement of wear performance. The 3D morphology of the surface of the counterpart ring was also used to discuss the wear mechanism of PPS composite coatings.     

Improved mechanical properties of carbon fiber reinforced PTFE composites by growing graphene oxide on carbon fiber surface

The mechanical properties of carbon fiber reinforced polymer composites depend upon fiber-matrix interfacial properties. To improve the mechanical properties of ?bers/PTFE composites without sacri?cing tensile strength of ?bers, graphene oxide (GO) was introduced onto the surface of CFs by chemical vapour deposition (CVD). This hybrid coating increased the wettability and surface roughness of carbon fibers, which led to improved affinity between the carbon fibers and PTFE matrix. The resulting hybrid-coated carbon fiber-reinforced composites showed an enhancement in the short beam strength compared to un-coated carbon fiber composites. Meanwhile, a signi?cant increase of interlaminar shear strength (ILSS), interface shear strength tests (IFSS) and impact property were achieved in the 5-min-modi?ed CFs.     

Converting ultrasonic induction heating deposited monetite coating to Na-doped HA coating on H2O2-treated C/C composites by a two-step hydrothermal method

a monetite coating on H₂O₂-treated C/C composites was prepared by ultrasonic induction heating (UIH) technology. Subsequently, this coating was subjected to an ammonia hydrothermal treatment to form a undoped hydroxyapatite (U-HA) coating. Finally, the as-prepared U-HA coating was placed in a NaOH solution and hydrothermally treated to produce the other hydroxyapatite (Na-HA) coating. The structure, morphology and chemical composition of the two HA coatings were characterized by XRD, FTIR, SEM and EDS, the adhesiveness and local mechanical properties, e.g. nanohardness and Young's modulus of the two HA coatings to C/C composites was evaluated by a scratch test and nanoindentation technique respectively. The results showed that the two HA coatings had the alike morphology and crystallization. But, compared with the U-HA coating, the Na-HA coating was doped with Na ions, and gave a Ca/P ratio close to a stoichiometric hydroxyapatite, and thus showed a higher nano-indentation value, Young's modulus, and larger bonding strength. These results verified the strengthened effect of Na ion in hydroxyapatite coating on carbon/carbon (C/C) composities.     

Enhanced interfacial adhesion between PMMA and carbon fiber by graphene oxide coating

The purpose of this study is to increase the interfacial properties in PMMA/carbon fiber (PMMA/CF) composites Graphene oxide (GO) and brached polyethyleneimine were coated onto the surface of carbon fiber by layer-by-layer assembly in this work. Compared with the origin PMMA/CF composite, the composites reinforced by PMMA/CF–GO showed significant enhancement in interFacial shear strength (IFSS). The improved fiber–matrix adhesion was proved by fracture morphology observation of scanning electron microscopy and almost unaffected mechanical properties of the fiber itself during the coating process. The optimal assembly time was found to be 10 for enhancing the overall composite mechanical performance.     

Improving the Mechanical Properties of Polycarbonate Nanocomposites with Plasma‐Modified Carbon Nanofibers

The mechanical properties of polycarbonate film embedded with carbon nanofibers were studied based on plasma surface modification of carbon nanofibers by the use of polystyrene. The nanofiber surfaces were modified by various processing conditions including plasma polymerization power, nanofiber concentration, and ultrasonication time. The tensile strength and Young's modulus of the carbon nanofiber‐polycarbonate composites were then measured. The mechanical behavior of the composite was found to be affected by dispersion of the nanofibers. Higher plasma power resulted in improved mechanical strength. A maximum strength (10% increase) was achieved at a low concentration (1 wt.%) of nanofibers. The optimization of ultrasonication time indicated that the maximum strength occurred at different times for the composites with different concentrations of the modified carbon nanofibers.     

Performance of glass woven fabric composites with admicellar-coated thin elastomeric interphase

Adequate stress transfer between the inorganic reinforcement and surrounding polymeric matrix is essential for achieving enhanced structural integrity and extended lifetime performance of fiber-reinforced composites. The insertion of an elastomeric interlayer helps increase the stress-transfer capabilities across the fiber/matrix interface and considerably reduces crack initiation phenomena at the fiber ends. In this study, admicellar polymerization is used to modify the fiber/matrix interface in glass woven fabric composites by forming thickness-controlled poly(styrene-co-isoprene) coatings. These admicellar interphases have distinct characteristics (e.g. topology and surface coverage) depending on the surfactant/monomer ratios used during the polymerization reaction. Overall, the admicellar coatings have a positive effect on the mechanical response of resin transfer molded, E-glass/epoxy parts. For instance, ultimate tensile strength of composites with admicellar sizings improved 50–55% over the control-desized samples. Interlaminar shear strength also showed increases ranging from 18 to 38% over the same control group. Interestingly, the flexural properties of these composites proved sensitive to the type of interphase formed for various admicellar polymerization conditions. Higher surface coverage and film connectedness in admicellar polymeric sizings are observed to enhance stress transfer at the interfacial region.     

Microstructure and wear resistance of Al–SiC composites coatings on ZE41 magnesium alloy

Al and Al–SiC composites coatings were prepared by oxyacetylene flame spraying on ZE41 magnesium alloy substrates. Coatings with controlled reinforcement rate of up to 23 vol.% were obtained by spraying mixtures containing aluminium powder with up to 50 vol.% SiC particles. The coatings were sprayed on the magnesium alloy with minor degradation of its microstructure or mechanical properties. The coatings were compacted to improve their microstructure and protective behaviour. The wear behaviour of these coatings has been tested using the pin-on-disk technique and the reinforced coatings provided 85% more wear resistance than uncoated ZE41 and 400% more than pure Al coatings.     

Effect of the molecular weight of sizing agent on the surface of carbon fibres and interface of its composites

The influence of different molecular weight sizing agent on the performances of carbon fibres and carbon fibres composites were studied. Three different kinds of molecular weight sizing were used. Surface composition of the fibres modified with aqueous sizing and topographies of carbon fibres surface were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and scanning electron microscope (SEM). The interlaminar shear strength and hygrothermal ageing test have been used to study the effect of fibres coatings on the adhesion of surface. The results of the study indicate that the molecular weight of sizing agent has an important influence to the carbon fibres and carbon fibres composites. The high and low molecular weight sizing agent decreased the interfacial shear strengths and hygrothermal ageing of carbon fibres composite. The moderate molecular weight of sizing agent showed an improvement of the interfacial adhesion and hygrothermal ageing.     

Corrosion and oxidation properties of NiCr coatings sprayed in presence of gas shroud system

The oxidation of a NiCr bond coat during air plasma spraying was controlled by designing a gas shroud system attached to the plasma torch nozzle. Two nozzles, termed as “normal” and “high-speed” nozzles examined the effect of nozzle internal design on the microstructure and phase structure of coatings. X-ray diffraction and SEM morphologies showed that the shroud system reduced the oxidation of NiCr particles during the spray process. Compared with conventional air plasma spraying, the argon gas shroud reduced the coating hardness because the volume fraction of partially melted particles increased. The high-speed nozzle reduced the oxidation and hardness of NiCr coatings due to the increase of partially melted particles in the coatings.     

Effect of chemical etching on the Cu/Ni metallization of poly (ether ether ketone)/carbon fiber composites

Poly(ether ether ketone)/carbon fiber composites (PEEK/Cf) were chemical etched by Cr₂O₃/H₂SO₄ solution, electroless plated with copper and then electroplated with nickel. The effects of chemical etching time and temperature on the adhesive strength between PEEK/Cf and Cu/Ni layers were studied by thermal shock method. The electrical resistance of some samples was measured. X-ray photoelectron spectroscopy (XPS) was used to analyze the surface composition and functional groups. Scanning electron microscopy (SEM) was performed to observe the surface morphology of the composite, the chemical etched sample, the plated sample and the peeled metal layer. The results indicated that CO bond increased after chemical etching. With the increasing of etching temperature and time, more and more cracks and partially exposed carbon fibers appeared at the surface of PEEK/Cf composites, and the adhesive strength increased consequently. When the composites were etched at 60 °C for 25 min and at 70-80 °C for more than 15 min, the Cu/Ni metallization layer could withstand four thermal shock cycles without bubbling, and the electrical resistivity of the metal layer of these samples increased with the increasing of etching temperature and time.     

Interphase sizing temperature effect of LaRC PETI-5 on the dynamic mechanical thermal properties of carbon fiber/BMI composites

The dynamic mechanical thermal properties of carbon fiber-reinforced bismaleimide (BMI) composites processed using polyacrylonitrile(PAN)-based carbon fibers unsized and sized with LaRC PETI-5 amic acid oligomer as interphase material at 150°C, 250°C, and 350°C were investigated by means of dynamic mechanical thermal analysis. It was found that the storage modulus, loss modulus, tan δ and the peak temperature significantly depend on the sizing temperature as well as on the presence and absence of LaRC PETI-5 sizing interphase. The result showed that the carbon fiber/BMI composite sized at 150°C had the highest storage modulus at a measuring temperature of 250°C. The storage modulus decreased with increasing sizing temperature from 150°C to 350°C, being influenced by interdiffusion and co-reaction between the LaRC PETI-5 interphase and the BMI matrix resin. The present result is quite consistent with the interfacial result reported earlier in term of interfacial shear strength and interlaminar shear strength of carbon fiber/BMI composites. It is addressed that in the present composite system the sizing temperature of LaRC PETI-5 interphase critically influences not only the interfacial properties but also the dynamic mechanical thermal properties and its control is also important.     

Formation of titania composite coatings on carbon steel by plasma electrolytic oxidation

Titania composite coatings were prepared on carbon steel by plasma electrolytic oxidation in silicate electrolyte and aluminate electrolyte with titania powers doping in the electrolytes. The microstructure of the coatings was characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The properties of the coatings including bond strength, thickness, thermal shock resistance and corrosion resistance varying with the quantities of titania powers in the electrolytes were studied. Investigation results revealed that the coating obtained in silicate electrolyte was composed of anatase-TiO₂, rutile-TiO₂ crystal phases and some Fe, Si, P elements; coating obtained in aluminate electrolyte consisted of anatase-TiO₂, Al₂TiO₅ and some Fe, P elements. Coatings obtained in two types of electrolytes show porous and rough surface. With increasing the concentration of titania powers in the electrolytes, the coating surface first became more compact and less porous and then became more porous and coarse. The bond strength and thickness were not strongly affected by concentration of titania powers in electrolytes. The valves were 23 MPa and for 66 μm for coatings obtained in aluminate electrolyte, and 21 MPa and 35 μm for coatings obtained in silicate electrolyte. Coatings obtained in silicate electrolyte showed a little better thermal shock resistance than those obtained in aluminate electrolyte and the best coatings were obtained with middle concentration of titania powers in the electrolytes. All coated samples showed better corrosion resistance than the substrate in 3.5 wt% NaCl solution. The best coatings were also obtained with middle concentration of titania powers doping in both electrolytes whose corrosion current density was decreased by 2 orders of magnitude compared with the substrate.     

Plasma treatment of carbon fibers: Non-equilibrium dynamic adsorption and its effect on the mechanical properties of RTM fabricated composites

The effect of oxygen plasma treatment on the non-equilibrium dynamic adsorption of the carbon fabric reinforcements in RTM process was studied. 5-Dimethylamino-1-naphthalene-sulfonylchloride (DNS-Cl) was attached to the curing agent to study the change of curing agent content in the epoxy resin matrix. Steady state fluorescence spectroscopy (FS) analysis was used to study this changes in the epoxy resin at the inlet and outlet of the RTM mould, and XPS was used to study the chemical changes on the carbon fiber surfaces introduced by plasma treatment. The interlaminar shear strength (ILSS) and flexural strength were also measured to study the effects of this non-equilibrium dynamic adsorption progress on the mechanical properties of the end products. FS analysis shows that the curing agent adsorbed onto the fiber surface preferentially for untreated carbon fiber, the curing agent content in the resin matrix maintain unchanged after plasma treatment for 3 min and 5 min, but after oxygen plasma treatment for 7 min, the epoxy resin adsorbed onto the fiber surface preferentially. XPS analysis indicated that the oxygen plasma treatment successfully increased some polar functional groups concentration on the carbon fiber surfaces, this changes on the carbon fiber surfaces can change the adsorption ability of carbon fiber to the resin and curing agent. The mechanical properties of the composites were correlated to this results.     

The effect of surface treatment of carbon fiber on the flexural property of thermoplastic polyimide composite

Rare earth solution (RES) surface modification and air-oxidation methods were used to improve the interfacial adhesion of the carbon fiber reinforced polyimide (CF/PI) composite. The flexural property of the PI composites reinforced by the carbon fibers treated with different surface modification methods was comparatively investigated. Results showed that the flexural strength of CF/PI composite was improved after RES treatment. The improvement of impact and flexural property of the CF/PI composite was mainly due to the improvement in interfacial adhesion after RES treatment. X-ray photoelectron spectroscopy (XPS) study of carbon fiber surface showed that the oxygen concentration was obviously increased after RES treatment. The increase in the amount of organic functional groups increased the interfacial adhesion between CF and PI matrix.     

Effect of gun current on the microstructure and crystallinity of plasma sprayed hydroxyapatite coatings

Hydroxyapatite (HA) is a bioactive material because its chemical structure is close to the natural bone. Its bioactive properties make it attractive material in biomedical applications. Gas tunnel type plasma spraying (GTPS) technique was employed in the present study to deposit HA coatings on SUS 304 stainless steel substrate. GTPS is composed of two plasma sources: gun which produces internal low power plasma (1.3-8 kW) and vortex which produces the main plasma with high power level (10-40 kW). Controlling the spraying parameters is the key role for spraying high crystalline HA coatings on the metallic implants. In this study, the arc gun current was changed while the vortex arc current was kept constant at 450 A during the spraying process of HA coatings. The objective of this study is to investigate the influence of gun current on the microstructure, phase crystallinity and hardness properties of HA coatings. The surface morphology and microstructure of as-sprayed coatings were examined by scanning electron microscope. The phase structure of HA coatings was investigated by X-ray diffraction analysis. HA coatings sprayed at high gun current (100 A) are dense, and have high hardness. The crystallinity of HA coatings was decreased with the increasing in the gun current. On the other hand, the hardness was slightly decreased and the coatings suffer from some porosity at gun currents 0, 30 and 50 A.     

Nanostructured TiN coating prepared by reactive plasma spraying in atmosphere

In the present study, the nanostructured TiN coatings are obtained by means of reactive plasma spraying in the air. The XRD analysis shows the coating was mainly composed of TiN (max. 86.3%) and a small quantity of Ti₃O. Their microstructures were observed by SEM and TEM. The TEM pictures show the TiN coatings were composed of the nanoscaled grains (range from 70 to 90 nm), and the Scherrer equation analysis on the average grain size corresponded with that result. The effects on the average grain size also were studied by changing the spraying power and the spraying distance.