Tribological behavior of poly (phenyl p-hydroxybenzoate)/polytetrafluoroethylene composites filled with hexagonal boron nitride under dry sliding condition

The sliding friction and wear behavior of polytetrafluoroethylene (PTFE) composites filled with poly (phenyl p-hydroxybenzoate) (PHBA) and hexagonal boron nitride (h-BN) was investigated with a pin-on-disc tester. The tensile properties, ball indentation hardness, impact strength and thermal diffusivity were measured. The test results in this paper indicate that the tensile strength, elongation at break, and impact strength decreased, however, the ball indentation hardness and thermal diffusivity were increased when the content of h-BN was increased. PTFE composites filled with 20 wt% PHBA and 20 wt% h-BN exhibited a comparative friction coefficient to pure PTFE. Meantime, the wear rate of the composite decreased about 15 times compared to pure PTFE. The synergistic effect of h-BN with low friction and PHBA with high bearing ability promoted the low friction coefficient and wear rate of h-BN/PHBA/PTFE composites.     

Sintering and densification mechanisms of tantalum carbide ceramics

Dense tantalum carbide (TaC) ceramics were prepared using TaC nanopowder via spark plasma sintering (SPS). The effects of the sintering temperature and applied pressure on the densification and grain growth behaviour of TaC ceramics were investigated. The results showed that high temperature and pressure promoted sintering densification, while their increase caused an increase in the grain size of TaC ceramics. A highly dense TaC ceramic (∼97.19%) with a fine grain size of 2.67 μm was obtained by sintering at 1800 °C for 10 min under 80 MPa. The Vickers hardness, Young's modulus and fracture toughness were 15.60 GPa, 512.66 GPa and 3.59 MPa·m^1/2, respectively. The densification kinetics were investigated using a creep deformation model. Diffusion and grain boundary sliding were proven to be the dominant densification mechanisms based on the stress and grain size exponents combined with the microstructural characteristics. The apparent activation energy of the mechanism controlling densification was 252.94 kJ/mol.     

Scratch induced failure of plasma sprayed alumina based coatings

A set of plasma sprayed coatings were obtained from three alumina based top coat and two bond coat powders. Scratch test was undertaken on these coatings, under constant and linearly varying load. Test results include the lateral force data and scanning electron microscope (SEM) images. Failure occurred by large area spallation of the top coat and in most cases tensile cracks appeared on the exposed bond coat. The lateral force showed an increasing trend with an increase in normal load up to a certain point and beyond this, it assumed a steady average value. The locations of coating spallation and occurrence of maximum lateral force did not coincide. A bond coat did not show a significant role in determining the scratch adhesion strength.     

类富勒烯结构对含氢碳膜摩擦学性能的影响

目的研究类富勒烯结构含氢碳膜的摩擦学性能及润滑机理。方法采用闭合场非平衡反应磁控溅射技术,通过调节靶电流制备出类富勒烯结构含氢碳膜(FL-C:H)与非晶含氢碳膜(a-C:H)。通过扫描电子显微镜、原子力显微镜观察薄膜表面与断面的形貌,通过傅里叶红外光谱仪表征了碳膜的碳氢键结构,通过纳米压痕仪、划痕仪、摩擦磨损实验评价薄膜的力学及摩擦学性能,通过透射电子显微镜分析磨屑结构,并通过光学显微镜及三维轮廓仪对磨斑及磨痕形貌进行分析。结果类富勒烯结构对薄膜的机械力学性能影响不大,但是对其大载荷下的摩擦学性能有影响。与a-C:H碳膜相比,小载荷下(5 N),FL-C:H碳膜的摩擦系数较高,大载荷下(20 N),FL-C:H碳膜具有较低的摩擦系数(0.03)和磨损率(4.8×10-8 mm~3/(m·N)),并且其摩擦界面形成了类球状纳米结构颗粒。随着载荷的增加,FL-C:H碳膜的摩擦系数和磨损率先降低,后基本不变,在载荷大于15 N时,摩擦界面形成了类球状纳米结构颗粒。结论类球状纳米结构颗粒的形成能降低薄膜的摩擦系数和磨损率,而FL-C:H碳膜比a-C:H碳膜更易在摩擦界面形成类球状纳米结构颗粒。这种类球状纳米结构的形成还依赖于载荷的大小(大载荷时更易形成),因此类富勒烯碳膜在大载荷下更易保持低的摩擦系数及磨损率。     

Effect of phenoxy-based coating resin for reinforcing pitch carbon fibers on the interlaminar shear strength of PA6 composites

Carbon fiber-reinforced thermoplastic composites have not been considered as constituent materials for structural parts due to the poor interfacial adhesion between the fiber and the thermoplastic matrix. In this work, polyamide 6 (PA6) composites with pitch carbon fibers (pCF) were fabricated by alternatively stacking PA6 films and pCF fabrics followed by being pressed. In order to improve the interfacial adhesion, phenoxy resin-based materials were coated on the surface of the fiber. The surface analyses of the fiber were carried out by XPS, TGA and dynamic contact angle method. Interlaminar shear strength (ILSS) of the composites was measured to evaluate the effect of the coating materials. The results showed that the composites with the coated pCF had higher ILSS than that with neat pCF by more than 20%. This indicated that a proper coating material can improve mechanical properties of the PA6 composites, which can be applied to the structural parts.     

Structure and conducting properties of thermoplastic composites of polypropylene and polyaniline protonated in solid state

The paper presents results of studies on composites made from polypropylene (PP) modified with polyaniline (PANI) doped with phenylophosphonic acid (PPA). For better miscibility of the components, lauryl gallate (LG) was added. Obtained results show that the amount of PPA and LG affect the thermal and structural properties of the composites. Changes of thermal properties, and particularly of structure, caused by addition of PPA and LG, affect the conductivity of the composites. The results discussed in the paper were obtained using differential scanning calorimetry (DSC) and optical microscopy as well as wide angle X-ray scattering (WAXS) and small angle X-ray scattering (SAXS).     

Friction-induced physical and chemical interactions among diamond-like carbon film,steel ball and water and/or oxygen molecules

Friction and wear behaviors of diamond-like carbon (DLC) film sliding against steel ball were investigated on a ball-on-disk test rig at different relative humidity (RH) in a nitrogen environment. The worn surface morphology of the steel ball was observed on a scanning electron microscope (SEM), while the chemical states of some typical elements on the worn surface of DLC film were investigated by means of X-ray photoelectron spectroscopy (XPS). The result showed that the DLC film recorded continuously increased friction coefficient and wear rate with increasing relative humidity from 5% to 100%. In dry nitrogen (RH < 5%), thick and compact transferred carbon-rich layer was observed covering on the worn surface of steel ball, while the chemical states of the original and worn film surface showed no obvious change. In humid nitrogen, distinct changes of the chemical states on the worn surface of DLC film took place, indicating that tribochemical reactions such as the oxidation of DLC film and the interactions between DLC film and steel ball were involved in the friction process. Therefore, it was proposed that the friction and wear behaviors of DLC film were dependent on the friction-induced physical and chemical interactions among DLC film, steel ball and water and/or oxygen molecules. The roles of environment in the friction and wear behaviors of DLC film were discussed in terms of the friction-induced physical and chemical interactions.     

Experimental studies on critical compositions for fabricating single-phase high entropy carbides based on the calculated phase diagram of (VNbTaMoW)0.5Cx (0 < x < 0.6)

In this paper, the phase diagram of (VNbTaMoW)_0.5C_x (0 < x < 0.6) was first calculated. We establish the complete phase diagram in two spatial dimensions from analysis the statistics of order phase parameters. To obtain high-entropy carbides and validate the calculated results, a series of (VNbTaMoW)C were sintered at different temperature. The single-phase carbide of (VNbTaMoW)C were synthesized at 1800 °C, which is higher than the theoretically calculated temperature in phase diagram. The reason is that the estimated temperature was calculated by mixing entropy for experimentally reported ideal solid solution models that simplified the temperature dependent parameters. Phase composition of (VNbTaMoW)C sintered at/below 1800 °C agrees well with the calculation results in phase diagram. Furthermore, we have systematically investigated the single-phase formation ability of four-metal and three-metal composition based on five elements (V, Nb, Ta, Mo, W). A total of 5 types of four-metal compositions and 10 types of three-metal compositions can be generated. However, for each composition, only 4 kinds four-metal and 6 kinds three-metal compositions can form single phase carbides. Those as-prepared single-phase carbides exhibit enhanced mechanical properties compared to the calculated values according to the rule of mixtures from constituent monocarbides.     

Adjustable TiN coatings deposited with HiPIMS on titanium bipolar plates for PEMFC

TiN coatings were deposited by HiPIMS at different N₂ flow rate to improve the corrosion resistance and conductivity of metallic bipolar plates. The results show that the surface microstructure of TiN coating depends strongly on the N₂ flow rate, all the samples (N₂ flow rate: 4 to10 sccm) meet the DOE 2025 standard and exhibit good hydrophobicity, which has great potential for industrial application. Among them, at the N₂ flow rate of 8 sccm, the TiN coating shows high compactness and the optimum surface microstructure with the lowest surface roughness of 1.083 nm and the highest hardness of 31.172 GPa. The optimized TiN coating exhibits excellent corrosion resistance with corrosion current density of 0.278 μA cm^?2 and a low interfacial contact resistance value of 3.51 mΩ cm². This work has opened a new way for the large-scale preparation of high-performance metal bipolar plate coatings.