Effect of void formation during MEVVA tungsten ion implantation on the microstructure and surface properties of H13 die steel

H13 die steel was implanted with tungsten using a metal vapour vacuum arc (MEVVA) ion source. When the pulsed beam current density of tungsten ions increased to 6mA?cm^-2, some voids appeared in the high voltage electron microscope (HVEM) micrograph, which would disappear at an annealing temperature of 600℃. HVEM and x-ray diffraction were used for observing the phase structure of the annealed and un-annealed H13 steel after the steel was implanted. Results of wear and hardness tests indicated that whether the voids appear significantly influences the hardness and wear of H13 steel. Reasons for the formation of voids and the relation between the surface mechanical property and voids are discussed in terms of collision theory.     

激光熔覆原位合成Nb(C,N)陶瓷颗粒增强铁基金属涂层

采用预涂粉末激光熔覆技术,在42CrMo基体上制备出原位合成Nb(C, N)颗粒增强的铁基复合涂层。X射线及扫描电镜分析结果表明：激光熔覆获得的涂层基体为耐氧化、耐蚀性良好的Fe-Cr细晶组织及少量的-Fe相,原位合成的Nb（C, N）呈块状弥散分布在基体上。进一步的磨损试验表明：这些颗粒增强相极大增强了抗磨损性能,与未熔覆的母材相比,其磨损失重仅为母材的1/9左右; 涂层在750 ℃恒温氧化条件下具有较好的抗氧化性能,氧化层主要由NbO1.1,Cr2O3相组成; 母材的氧化产物为Fe2O3,容易脱落,保护性能较差; 激光熔覆涂层的氧化膜厚度仅为未涂层的1/5。     

Degradation patterns and surface wettability of electrospun fibrous mats

Degradation profiles and surface wettability are critical for optimal application of electrospun fibrous mats as drug carriers, tissue growth scaffolds and wound dressing materials. The effect of surface morphologies and chemical groups on surface wettability, and the resulting matrix degradation profiles were firstly assessed for electrospun poly(d,l-lactide) (PDLLA) and poly(d,l-lactide)-poly(ethylene glycol) (PELA) fibers. The air entrapment between the fiber interfaces clarified the effects of various surface morphologies on the surface wettability. Chemical groups with lower binding energy were enriched on the fiber surface due to the high voltage of the electrospinning process, and a surface erosion pattern was detected in the degradation of electrospun PDLLA fibers, which was quite different from the bulk degradation pattern for other forms of PDLLA. Contributed by the hydrophilic poly(ethylene glycol) segments, the degradation of electrospun PELA fibers with hydrophobic surface followed a pattern different from surface erosion and typical bulk degradation.     

Effect of Y2O3 on microstructural characteristics and wear resistance of cobalt‐based composite coatings produced on TA15 titanium alloy surface by laser cladding

The effects of Y₂O₃ on the microstructure, phase composition of the coatings, microhardness and wear resistance of cobalt‐based composite coatings prepared by laser cladding were investigated. The TA15 titanium alloy was selected as substrate which the cobalt‐based composite powder with different content of Y₂O₃ was cladded on. The microstructure of the coatings was observed by scanning electron microscope (SEM) and metallurgical microscope. The phase structure of the coatings was determined by X‐ray diffraction (XRD), and the microhardness and wear resistance of the coatings were measured by hardness tester and wear testing machine. The results show that the rare earth oxide Y₂O₃ can refine and purify the microstructure of the coatings, reduce the porosities and cracks and improve compactness of the coatings. Moreover the addition of Y₂O₃ improves the microhardness of the coatings and reduces the friction coefficient, thus improving the wear property of the coatings. And the wear resistance of the coating with Y₂O₃ has improved about 50 times; the highest value of microhardness in the coating is HV1181.1. And 0.8 wt% content of Y₂O₃ in the coating is the best choice for improving the microhardness and wear resistance of the coating. It is feasible to improve the microstructure and tribological properties of laser cladding coatings by adding of Y₂O₃. Copyright © 2014 John Wiley & Sons, Ltd.     

Enhanced Physical and Mechanical Properties of Nitrile-Butadiene Rubber Composites with N-Cetylpyridinium Bromide-Carbon Black

The physical and mechanical properties of nitrile–butadiene rubber (NBR) composites with N-cetylpyridinium bromide-carbon black (CPB-CB) were investigated. Addition of 5 parts per hundred rubber (phr) of CPB-CB into NBR improved the tensile strength by 124%, vulcanization rate by 41%, shore hardness by 15%, and decreased the volumetric wear by 7% compared to those of the base rubber-CB composite.     

Spectroscopic study of a magnetically rotating arc between opper electrodes in contaminated argon

The effects of N₂ and CO contaminants in atmospheric-pressure argon on an arc rotating between two concentric copper electrodes has been studied using optical spectroscopy of copper lines. The axial temperature of the magnetically driven arc in Ar + %N₂ was determined to be around 10,000 K for arc currents of SO to 200 A. The diffusion process of the copper vapor from the cathode was also studied. A copper density maximum 1 mm from the cathode along the arc column was found in Ar + %N₂. Removal of the contaminated cathode surface layers by the arc when contaminant injection in the plasma gas was stopped was found to be a slow process with a time scale depending on the type of the gas contaminant. The presence of gas contaminant in the electrode material controls the cathode erosion mechanism and the overall arc behavior in the transition between a contaminated to a pure argon arc.     

The effect of low concentrations of a polyatomic gas in argon on erosion on copper cathodes in a magnetically rotated arc

Experimental results are presented for electrode erosion on copper cathodes in magnetically rotated arcs in argon, dry air, nitrogen, ammonia, and carbon monoxide as well mixtures of the above with argon. Water-saturated argon was also used. Erosion rates were determined by weight loss after chemical cleaning, and the runs were sufficiently long (between 5 to 60 min) to represent steady-state operation. Arc currents of 100 A and gas pressures of 1.1 atm. were used. Pure argon gave the highest erosion rates and the lowest arc velocities. Small concentrations of any of the diatomic gases in argon greatly increased the arc velocity and decreased the erosion rates. The results suggest that erosion is primarily a thermal phenomenon but that the surface chemistry can greatly influence erosion rates by modifying arc behavior.     

Surface modification and wear test of carbon steel by plasma electrolytic nitrocarburizing

Plasma electrolytic nitrocarburizing (PEN/C) was applied to the surface of carbon steel under the boiling condition of saturated urea electrolyte. In addition to the general effect of the bath temperature, different applied voltages and processing times were also considered in this new process. Optical and scanning electron microscopy, X‐ray diffraction, microhardness and pin‐on‐disc wear tests were used to characterize the PEN/C‐treated surfaces. A mixture of θ‐(Fe₃C) and ε‐(Fe_2–3N) was found in the compound layers. At certain conditions, dense surface layers with minimum porosity were observed at the top of the samples. The boiling condition resulted in special character of the compound layers on the surface. The layers consisted of some irregularities grown inward the samples andaffected the characteristics of the surface layers. The microhardness of the PEN/C‐treated layers increased up to 1280 HV0.1, which was 3 to 4 times higher than that for untreated material and higher than that obtained by other investigators (750 HV0.1). PEN/C decreased the wear loss of carbon steel significantly due to the change of the adhesive wear of untreated material to the abrasive mode of treated surfaces. The major advantage of this technique was a higher growth rate of the nitrocarburized layers and a more significant improvement in the tribological performance of the treated samples if compared to similarly oriented surface treatments. Copyright © 2011 John Wiley & Sons, Ltd.     

Effects of atomic oxygen irradiation on structural and tribological properties of polyimide/Al2O3 composites

To understand the effects of atomic oxygen (AO) irradiation on the structural and tribological behaviors of polymer composites, polyimide/Al₂O₃ composites were irradiated with AO in a ground‐based simulation facility. The structural changes were characterized by X‐ray photoelectron spectroscopy and attenuated total‐reflection FTIR, whereas the tribological changes were evaluated by friction and wear tests as well as scanning electron microscopy analysis of the worn surfaces. It was found that AO irradiation induced the oxidation and degradation of polyimide molecular chains, which increased the O concentration and decreased the C concentration in the composite surfaces. The destruction action of AO changed the surface chemical structure and morphology of the samples. Friction and wear tests indicated that AO irradiation decreased the friction coefficient but increased the wear rate of both pure and Al₂O₃ filled polyimides. In terms of the tribological properties, appropriate content of Al₂O₃ might be favorable for the improvement of tribological properties in AO environment. Copyright © 2011 John Wiley & Sons, Ltd.     

Enhancement of water barrier properties and tribological performance of hybrid glass fiber/epoxy composites with inclusions of carbon and silica nanoparticles

Water barrier properties and tribological performance (hardness and wear behavior) of new hybrid nanocomposites under dry and wet conditions were investigated. The new fabricated hybrid nanocomposite laminates consist of epoxy reinforced with woven and nonwoven tissue glass fibers and two different types of nanoparticles, silica (SiO₂) and carbon black nanoparticles (C). These nanoparticles were incorporated into epoxy resin as a single nanoparticle (either SiO₂ or C) or combining SiO₂ and C nanoparticles simultaneously with different weight fractions. The results showed that addition of carbon nanoparticles with 0.5 and 1 wt% resulted in maximum reduction in water uptake by 28.55% and 21.66%, respectively, as compared with neat glass fiber reinforced epoxy composites. Addition of all studied types and contents of nanoparticles improves hardness in dry and wet conditions over unfilled fiber composites. Under dry conditions, maximum reduction of 47.26% in weight loss was obtained with specimens containing 1 wt% carbon nanoparticles; however, in wet conditions, weight loss was reduced by 17.525% for specimens containing 0.5 wt% carbon nanoparticles as compared with unfilled fiber composites. Diffusion coefficients for different types of the hybrid nanocomposites were computed using Fickian and Langmuir models of diffusion. Copyright © 2017 John Wiley & Sons, Ltd.