Composition Of Surface Layer Research Articles

Composition of Surface Layers Prepared by Ion Beam Assisted Deposition of Catalytic Metals from Pulsed Arc-Discharge Plasma onto Carbon Paper Substrates

Composition of Surface Layers Prepared by Ion Beam Assisted Deposition of Catalytic Metals from Pulsed Arc-Discharge Plasma onto Carbon Paper Substrates

Mechanical properties and wear resistance of ZrO2 particulate-reinforced composite layer on compacted graphite cast iron processed by selective laser alloying

The authors report the fabrication of a particulate-reinforced composite layer on compacted graphite cast iron by means of selective laser alloying, reinforced with ZrO2 ceramic particulates. The scanning strategy was inspired by the alternate arrangement of aragonite and organic layers on the shell surface. The particulates were uniformly embedded in the matrix. Moreover, the original microstructure was significantly modified. The microhardness, tensile strength, and wear resistances, in particular, were notably improved, due to the formation of the surface composite layer. With the increasing content of the ceramic particulates, the mechanical properties and wear resistance are further enhanced. In particular, the wear mass loss is decreased by ∼90%. This is because: (1) the overall microhardness is increased; (2) the microstructure is significantly refined; (3) the coarse graphite disappears after laser treatment, and (4) above all, a laser-fabricated metallic matrix composite layer on the surface of the sample gave rise to enhanced properties.

Mehanizmi povečanja trdote površinskih slojev kompozitov zlitine Ti6Al4V med lasersko-plinskim nitriranjem

Mehanizmi povečanja trdote površinskih slojev kompozitov zlitine Ti6Al4V med lasersko-plinskim nitriranjem

Different Shades of Li4Ti5O12 Composites: The Impact of the Binder on Interface Layer Formation

AbstractReplacing the traditional PVdF(‐HFP) electrode binder with water‐soluble alternatives can potentially render electrode fabrication more environmentally benign. Herein, the surface layer formation of stored and cycled samples of two water‐based Li4Ti5O12 composites employing either poly(sodium acrylate) (PAA−Na) or sodium carboxymethyl cellulose (CMC−Na) as binders are studied with X‐ray photoelectron spectroscopy. In all three formulations, the surface layer composition formed upon storage differed notably from the solid‐electrolyte interphase (SEI) layer formed on cycled samples. The surface layer under open‐circuit conditions seems to originate mostly from the electrolyte salt (LiPF6) degradation. The comparison with cycled samples after 10 and 100 cycles shows a continuous build‐up of an SEI layer on PAA−Na and PVdF‐HFP electrodes. In contrast, on CMC−Na containing electrodes the SEI composition remains nearly unchanged. The results correlate well with the electrochemical behavior.

Microstructure and magnetic properties of strontium titanate implanted with iron

The magnetic phase composition of strontium titanate surface layers implanted with iron ions is studied by means of Mossbauer spectroscopy, and by measuring alternating current magnetic susceptibility. It is shown that the interaction between α-Fe nanoclusters at high concentrations of the implanted admixture produces ferromagnetic order in samples at room temperature.

Composition of Surface Layer at the Water\u2013Air Interface and Micelles of Triton X-100\xa0+\xa0Rhamnolipid Mixtures

Measurements of the surface tensions, densities and viscosities of aqueous solutions of Triton X-100 (TX-100) and rhamnolipid (RL) mixtures, at constant concentration of RL or TX-100, were carried out. The measured values of the surface tension were compared to those determined using different theoretical models and on the basis of the surface tension of aqueous solutions of individual surfactants. From the surface tension isotherms, the Gibbs surface excess concentration of TX-100 and RL, the composition of surface layer and the standard Gibbs free energy of adsorption at the water–air interface were determined. Moreover, on the basis of surface tension, density and viscosity isotherms, the CMC of surfactants mixtures were evaluated. From the density isotherms, apparent and partial molar volumes of TX-100 and RL were also determined. These volumes were compared to those calculated from the sizes of TX-100 and RL molecules. There was observed a synergetic effect in the reduction of water surface tension and micelle formation, which was confirmed by the intermolecular interactions parameter. In the case of micelle formation, this effect was discussed based on the standard Gibbs free energy of micellization as well as of TX-100 and RL mixing in the micelles. The synergism of TX-100 and RL mixtures in the reduction of water surface tension and micelle formation was explained on the basis of electrostatic interactions between the hydrophilic part of TX-100 and RL molecules; this was supported by pH measurements.

Diode Laser Surface Alloying of Armor Steel with Tungsten Carbide

AbstractMetal matrix composite (MMC) surface layers reinforced by WC were fabricated on armor steel ARMOX 500T plates via a laser surface alloying process. The microstructure of the layers was assessed by scanning electron microscopy and X-ray diffraction.The surface layers having the WC fraction up to 71 vol% and an average hardness of 1300 HV were produced. The thickness of these layers was up to 650 μm. The addition of a titanium powder in the molten pool increased the wettability of WC particles by the liquid metal in the molten pool increasing the WC fraction. Additionally, the presence of titanium resulted in the precipitation of the (Ti,W)C phase, which significantly reduced the fraction of W-rich complex carbides and improved a structural integrity of the layers.

Improvement of the Reciprocating Sliding Wear Resistance of a Nb-Based Alloy Using Thermal Oxidation

The influence of thermodiffusion oxidation on structure, physicomechanical and tribological properties of the niobium–titanium alloy has been analyzed. The temperature and time conditions for a formation of the composite diffusion layer with different contents of oxide inclusions have been established. The method of combined chemical and heat treatment of niobium–titanium alloy is proposed. The surface composite layer consists of the oxide inclusions of rutile-type Ti(Nb, Al, V)O2 in the matrix. In this case, the gas-saturated layer with the content of oxide inclusions of 40–50 vol.% is formed. It provides the increased wear resistance of the alloy.

Tribological behavior of copper-molybdenum disulfide composites

The dry sliding friction and wear behavior of Cu-MoS2 composite pins against bearing steel (AISI 52100) discs were investigated in order to determine the optimal additive content. The MoS2 content ranged from 0–40vol%. The microstructure and composition of the worn surface, wear debris and transfer layer were observed and analyzed in detail to reveal the dominant friction and wear mechanisms. It is confirmed that MoS2 is an effective lubricant for copper matrix composites against steel because the friction coefficient decreased from 0.67 to 0.18 when adding 20vol% of the MoS2. The wear rates of the composites tended first to increase then decrease as the MoS2 content increased. The high wear rates of Cu-5vol% MoS2 and Cu-10vol% MoS2 composites are mainly attributed to the cracks associated with the MoS2 particles, and the decrease of wear rate for composites with MoS2 above 20vol% is derived from the formation of a nearly continuous lubricating film on the worn surface. The formation mechanism for MoS2 lubricating film has been clarified by observing its microstructure and characterizing its distribution in the worn surface.

Assessment of microstructure and wear behavior of aluminum nitrate reinforced surface composite layers synthesized using friction stir processing on copper substrate

Aluminum nitride (AlN) is a potential ceramic particle to improve the wear resistance of copper surface. The present work is focused on synthesizing Cu/AlN (0,6,12,18vol%) copper matrix composites (CMCs) on pure copper substrates through friction stir processing (FSP). AlN particles were compacted into grooves machined on the surface of the copper plates. FSP was carried out under a set of fixed experimental conditions. The microstructural features were analyzed using optical, scanning and transmission electron microscopy. The wear behavior was assessed using a pin-on-disc apparatus. AlN particles were distributed homogenously in the surface composite. There were no clusters and segregation of AlN particles. The distribution was almost constant across the depth of the surface composite. There was a good interfacial bonding between AlN particles and the copper matrix. There was no major change in shape and size of AlN particles subsequent to FSP. Fine equiaxed grain structure was observed in the composite induced by dynamic recrystallization and pinning effect of AlN particles. The dry sliding wear behavior of the composite surface was reported in detail.

Engineering Palladium Surfaces to Enhance the Electrochemical Storage of Hydrogen

Materials can be engineered to have enhanced hydrogen storage capabilities during electrolysis by modifying the composition of the first few surface layers at the electrolytic interface. The proper choice of surface layer can radically affect the electrochemical insertion of hydrogen. To this end, between 1 μg cm−2 and 23 μg cm−2 of Pb was deposited onto Pd cathodes during galvanostatic experiments in the 0.1 M LiOH electrolyte. The optimum surface doping level 2.9 μg cm−2 (~1.4 mass equivalent monolayers) of Pb was found to achieve the highest quantity of inserted hydrogen at a potential of approximately −0.5 V vs RHE. Additionally, the hydrogen content increased from PdH0.75 to PdH0.86 with increasing Pb amounts up to 2.9 μg cm−2 at a constant current of −14.5 mA cm−2. For comparison, the same change in hydrogen content from pressurized gas loading experiments would require an increase in hydrogen fugacity from about 6 to 1420 atm. Furthermore, the addition of a small amount of Pt co-deposited with the Pb resulted in a further increase in hydrogen content to PdH0.89 at −14.5 mA cm−2. Preliminary analysis suggests the Pb and Pt are changing the balance between the Volmer, Heyrovsky, and Tafel reaction rates, which changes the chemical potential of the adsorbed hydrogen, and ultimately controls the hydrogen insertion. This work provides a fundamental basis for the future design of surface alloys yielding enhanced electrochemical hydrogen insertion in Pd and other hydrogen absorbing materials.

(Invited) Surface Composition and Structure Controlled High-Performance Electrohemicalcatalysts

Noble metal-based nanocrystals have played important roles in heterogeneous catalysts due to their high activity and chemical stability. The high cost of noble metals, however, created roadblocks for the large volume production of noble metal catalysts for many applications. Improving the catalytic activity or the efficiency of noble metal usage, and prolong the life-time of a noble metal based catalysts are solutions to these challenges. On a nanocatalyst, the composition, atomic coordination, and strains of the top surface layers eventually determine its performance in catalytic reactions. Slight changes in the surface structure of catalytic materials for example, such as increase in the number of accessible surface adsorption sites or generating uniform surfaces with abundant specific defects, can have large impacts on the catalytic stability and activity. In this presentation I will share our recent efforts on tuning the surface compositions and structures of noble metal catalysts to improve both catalytic activity and stability.

Stable Carbon Cathodes for Potassium-Oxygen Batteries

Among energy storage technologies beyond lithium-ion, alkali metal-oxygen batteries stand out for their unparalleled theoretical energy densities. Based on the reaction between dioxygen and alkali metal ions in non-aqueous electrolytes, metal-oxygen batteries could store up to 10 times more energy per unit mass (in the case of Li-O2) when compared to today’s lithium-ion batteries1. Despite extensive efforts elucidating the mechanism of the reaction between alkali cations and dioxygen, this technology is still far from maturing into a commercial device. The main drawbacks of Li-O2 systems are electrolyte and cathode instability, low conductivity of lithium peroxide (Li2O2) leading to poor cycleability. In contrast to Li-O2, potassium-O2 discharge reactions proceeds via a one electron reduction leading to potassium superoxide (KO2) as the sole discharge product2-5. Here, different carbon based cathodes were investigated in K-O2 cells. Furthermore the stability of the K metal anode with different non-aqueous electrolytes was compared. The cell capacity varied depending upon the cathodic carbon structure employed (Figure 1a). KO2 was the only discharge product identified via Raman spectroscopy (Figure 1b) and powder X-ray diffraction. FTIR spectra taken of the cathodes after first discharge, showed no evidence of carbonate species or other parasitic reaction products. These results are encouraging, since the large overpotential observed within Li-O2 cells was found to be related to side reactions on the carbon electrode surface6. The voltage gap in K-O2 cells was lower than 100 mV, and round trip efficiency, as high as 98%. The cycleability of the cells was found to be limited by side reactions between the potassium metal anode and ether-based electrolyte in the presence of dioxygen reduced species, rather than side reactions within the carbon cathode. The main components of this insulating anode surface layer were K2CO3, KOH and KO2. Similar anode surface layer composition was found for different combinations of ether electrolytes and potassium salts. However, while using super-concentrated electrolytes (3M and 5 M KTFSI in dimethoxyethane), O2 crossover was inhibited, and no KO2 was detected on the potassium metal anode surface. As a result, these cells were able to be cycled over 50 times under shallow cycling of 50 mAh/g. The superconcentrated electrolytes had no effect on the cathode reaction product, and the battery cycled through KO2 formation and oxidation. Capacity fade eventually occurred, as repetitive stripping/plating of K metal anode caused the disruption of the protective layer. This work highlights that once a suitable electrolyte has been selected, a metal-O2 cell can indeed be cycled numerous times. The challenge is to increase the cycleable capacity to more appealing values, whilst maintaining cell stability. [1] P.G. Bruce, S.A. Freunberger, L.J. Hardwick, J-M. Tarascon, Nature Mater. 11, 19 (2012). [2] X. Ren, Y. Wu, J. Am. Chem. Soc. 135, 2923 (2013). [3] X. Ren et al. ACS Appl. Mater. Interfaces 6, 19299 (2014). [4] W.D. McCulloch et al. ACS Appl. Mater. Interfaces 7, 26158 (2015). [5] X. Ren et. al. Adv. Energy. Mater. 1601080 (2016). [6] B.D. McCloskey et. al. J. Phys. Chem. Lett. 4, 2989 (2013). Figure 1

Effect of structural steel ion plasma nitriding on material durability in pulsed high magnetic fields

The work was aimed to study the influence of plasma nitriding on electrical and mechanical properties of structural steels and their durability in pulsed high magnetic field. The plates and cylindrical magnetic flux concentrators were made of several steel grades (30KhGS, 40Kh, 50KhGA, 38Kh2MYuA, and U8A), heat-treated, and subjected to the low-temperature (400, 500°C) plasma nitriding. Electrical and mechanical properties of materials, phase composition of steel surface layer, microstructure and microhardness profiles were investigated on the plates before and after plasma treatment. Microstructure and microhardness profiles across the subsurface layer of plasma treated and untreated concentrators applied for high magnetic field generation were also studied. Magnetic field of 50 T under tens of microseconds in duration inside the flux concentrators was generated by long-life outer coil.

Dynamics of titanium surface characteristics after its treatment by runaway electron preionized diffuse discharge

Ageing changes of the elementary composition of titanium surface (VT-1) treated by runaway electron preionized diffuse discharge in nitrogen at atmospheric pressure have been studied. Dependence of the elementary composition of titanium surface layers on surface free energy has been shown.

Modification of the Structural-Phase State of the Surface Layer of a Cermet Composite Under Electron Beam Irradiation in Inert Gas Plasmas

The results of investigation of characteristic features of modification of the structural-phase state of the surface layer of a TiC–(Ni–Cr) cermet composite under irradiation by a pulsed electron beam in the discharge plasma of inert gases with different atomic masses and ionization energies are presented. The effect of modification of the structural-phase state of the composite surface layer on its strength is analyzed under conditions of threepoint bending.

Акустична емісія при зносі обробного інструменту з не керованою глибиною різання

Мета: Метою роботи є дослідження акустичної емісії при механічній обробці композиційного матеріалу з не керованою глибиною різання і зносі ріжучого інструменту з композиційного матеріалу. Методи дослідження: В основі досліджень лежить моделювання акустичного випромінювання, яку виникає при руйнуванні поверхневого прошарку оброблюваного композиційного матеріалу і зносі обробного інструменту. Розглядався випадок переважного механічного руйнування поверхневого прошарку оброблюваного композиційного матеріалу, а знос інструменту відбувається без зміни глибини різання. Була проведена статистична обробка амплітудних параметрів акустичної емісії при відсутності і виникненні зносу обробного композиційного матеріалу. Був проведений аналіз закономірностей зміни амплітудних параметрів акустичної емісії, а також їх чутливості до зносу обробного композиційного матеріалу при не керованій глибині механічної обробки. Результати: Визначено, що зростання зносу обробного композиційного матеріалу супроводжується зменшенням статистичних амплітудних параметрів акустичної емісії – середнього рівня амплітуди, його стандартного відхилення та дисперсії. Отримано закономірності зменшення амплітудних параметрів акустичної емісії при зростанні зносу обробного композиційного матеріалу. Визначено процентне зменшення амплітудних параметрів акустичної емісії при зростанні зносу обробного композиційного матеріалу, по відношенню до їх значень без зносу інструменту. Показано, що зменшення дисперсії середнього рівня амплітуди акустичної емісії випереджає зменшення середнього рівня амплітуди и його стандартного відхилення. Обговорення: Проведено моделювання акустичного випромінювання при переважному механічному руйнуванні поверхневого прошарку оброблюваного композиційного матеріалу з не керованою глибиною різання і зносі обробного композиційного матеріалу. Показано, що зростання зносу інструменту приводить до зменшення статистичних амплітудних параметрів акустичного випромінювання. Визначено, що зменшення дисперсії середнього рівня амплітуди сигналів акустичної емісії випереджає зменшення середнього рівня амплітуди і його стандартного відхилення. Зменшення середнього рівня амплітуди акустичного випромінювання і величини його розкиду обумовлено різним вкладом складових сигналів акустичної емісії, які виникають при руйнуванні оброблюваного і зносі обробного композиційних матеріалів. Очевидно, що при зменшенні площі руйнування оброблюваного композиційного матеріалу зменшення амплітудних параметрів виникаючих сигналів випереджає зростання амплітудних параметрів сигналів, які виникають при зростанні зносу обробного композиційного матеріалу. Результати проведених досліджень можуть бути використані при розробці методів контролю стану ріжучого інструменту і управлінні параметрами технологічного процесу механічної обробки. Дані методи представляють інтерес в роботизованих технологічних процесах, контроль і управління якими можливо проводити через нейронні мережі.

Effects of Gas Nitriding Temperature on the Surface Properties of a High Manganese TWIP Steel

The effects of gas nitriding temperature on the cross section morphology, element nitrogen distribution, and surface layer compositions of a cold rolled and pre-strained high manganese austenitic TWIP steel 25Mn-3Cr-3Al-0.3C-0.01N and the corresponding anti-corrosion ability have been studied. The results show that, depending on nitriding temperature, the distribution of element nitrogen and main phase compositions are significantly different in the nitriding layers. At a temperature lower than 500 °C, the main composition in the modified layer is S-phase and the nitrogen concentration linearly decreases from the surface to the center, while Fe4N forms with S-phase and a step-like distribution of nitrogen content is present at nitriding temperature of 600 °C. Caused by the increasing of modified layer thickness and the formation of S-phase and Fe4N, the surface hardness was obviously enhanced. Anodic polarization curves in 3.5 wt. % NaCl solution indicate that the nitrided processes have a tremendous modification effect on anti-corrosion ability. Moreover, the increase of (111) oriented grain, caused by the elevated nitriding temperature, has a positive effect on the corrosion resistance.

Formation of Composite Surface Layers TiNiTa + cBN-Co-NiAl-Y Considering their Properties

We developed formation technology of composition "steel - material with shape memory effect - high-temperature ceramic wear layer" by means of high-velocity oxygen-fuel spraying in the protective environment of mechanically activated powders TiNiTa and cBN-Co-NiAl-Y. We determined optimal processing parameters. We revealed regularities in the formation of nanosized state composition on the basis of the complex X-ray diffraction and electron microscopy studies. We carried out tests om steel 1045 with a surface-modified layer TiNiTa + cBN-Co-NiAl-Y in high-cycle fatigue, which confirmed the increase in endurance limit.

Nickel‐aluminum‐bronze/Al2O3 surface nanocomposite produced by friction‐stir processing: Corrosion properties and microstructure

In this research, friction stir processing (FSP) was applied for fabricating nanosized particles of Al2O3 as a surface composite layer on nickel‐aluminum bronze alloy. In addition, the effect of nanosized Al2O3 on the microstructure, hardness, and corrosion resistance of the alloy surface was investigated. To study the microstructure of the FSP treated surface, optical and scanning electron microscopy were used. Moreover, the static immersion and electrochemically corrosion tests were employed to investigate the corrosion resistance of the FSP‐treated surface. The results indicated that using nanoparticles of Al2O3 to produce the surface nanocomposite layer led to fewer amounts of β transformation products. Furthermore, dynamic re‐crystallized sub‐grains were formed in α grains in the stir zone during severe plastic deformation. In addition, a significant improvement in the corrosion resistance of the alloy surface was observed in the friction stir processed nanocomposite sample in comparison to the one without nanoparticles.