Surface modifications induced by the friction of graphites against steel

Graphite is a well-known, multipurpose material used in many applications including tribology, electrochemistry and metallurgy. In this study, we focused our attention on the modifications of the surfaces of graphite pins, one natural and two synthetic, in dynamic contact against steel. Specifically, we explored the effect of the normal load applied to the contact, on the friction behaviour of graphites.The results of the series of tests under “low” loads indicated that the friction coefficient and the transfer film forming tendency increased with increasing load, due to the modification of the morphology of the contact area. Whereas experiments under “high” loads revealed the existence of a critical load at which a sudden decrease of both the coefficient of friction and the transfer film forming tendency is observed. The reorientation of the graphitic planes is supposed to be at the origin of this phenomenon.     

Surface micromorphology and abrasive wear resistance of tool steel after gas-laser cutting

The results of experimental studies into the surface micromorphology, microstructure, and microhardness of deposited P2M8 high-speed steel subjected to gas-laser cutting are presented. It is demonstrated that, in the area of laser action, the volume wear rate of high-speed steel is three times lower as compared to standard strengthening by means of volume hardening and triple tempering.     

Surface modifications for mechanical applications

Chemical and high energy beam conversion coatings, as well as PVD thin films, are characterised to correlate microstructures and mechanical properties. In particular, thermochemical boriding and laser surface melting are considered to produce conversion coatings on iron alloys, and physical vapour techniques to deposit thin films of titanium nitride on iron. The mechanisms leading to selected microstructures and, consequently, to improved surface and interface properties are discussed.     

Characterization of rapidly solidified powder of high-speed steel

Ionization and excitation cross sections as well as electron-energy spectra and stopping powers of the alkali metal atoms Li, Na, K, and Rb colliding with antiprotons were calculated using a time-dependent channel-coupling approach. An impact-energy range from 0.25 to 4000 keV was considered. The target atoms are treated as effective one-electron systems using a model potential. The results are compared with calculated cross sections for antiproton-hydrogen atom collisions.     

Surface modifications of materials by repetitive laser pulses

Laser-induced modifications on platinum (Pt) and silicon (Si) are compared by considering the development of various features on the irradiated surface. The experiments were carried out both in air and under vacuum. The interaction of 50 pulses of 1064 nm Nd:YAG laser with both targets in air resulted in non-linear phenomena. The periphery of the irradiated spot on the Pt surface exhibits wave-like patterns with a featureless central portion. A non-uniform distribution of cones of different sizes is also observed on the irradiated surface. In the case of silicon, the laser-induced periodic surface structures along with the formation of micro-column, rectangular blocks and grid are prominently observed features. However, when both the targets were irradiated with the same number of shots under vacuum (～10^?3 Torr), the surface morphologies of both the targets exhibited the hydrodynamic sputtering but with more explosive expulsion in Pt when compared with silicon. In platinum, there is a periodic variation in the distance between adjacent cones formed in various ablated zones. The Gaussian beam mode TEM₀₀ provided the evidences for melt pool formation in silicon when irradiated under vacuum. Additionally, we observed other mechanisms including splashing, sputtering, burning, re-solidification and redeposition on the surface of irradiated targets.     

Surface microwave discharge in high-speed air-hydrocarbon flows

The influence of nonequilibrium plasma of the surface microwave discharge on the ignition of supersonic (M = 2) propane-air flow, as well as alcohol, benzene, and kerosene for sub- and supersonic air flow is studied.     

Microstructure changes in high-speed hot rolling of steel rods

Transmission electron microscopy (TEM), quantitative texture analysis by means of neutron diffraction (QTA) and X-ray diffraction profile analysis (XDPA) were used to study the microstructure changes occurring in high-speed hot rolling ( 1500 s^–1;T=1073 K) of high-alloy stainless steel X8CrTi17 (ferrite) and X8CrNiTi18.10 (austenite). The investigations indicate that at higher deformation rates recrystallization due to adiabatic overheating becomes an important process of microstructure formation.     

Surface modifications by swift heavy-ion irradiation of indium phosphide

InP (001) samples were irradiated with 200 MeV Au ions at different fluences. The surface nanotopographical changes due to increasing fluence of swift heavy ions were observed by Atomic Force Microscopy (AFM), where the onset of a large increase in surface roughness for fluences sufficient to cause complete surface amorphization was observed. Transmission Electron Microscopy (TEM) was used to observe bulk-ion tracks that formed in InP, and high resolution TEM (HRTEM) revealed that single-ion tracks might not be amorphous in nature. Surface-ion tracks were observed by AFM in the form of ill-defined pits (hollows) of ~12 nm in diameter (width). In addition, Rutherford backscattering was utilized to follow the formation of disorder to amorphization in the irradiated material. The interpretation of the large increase in surface roughness with the onset of amorphization can be attributed to the plastic phenomena induced by the change of states from crystalline to amorphous by ion irradiation. The text was submitted by the authors in English.     

Surface modifications of ITO electrodes for polymer light-emitting devices

Surface modifications were performed on the indium tin oxide (ITO) substrates for polymer light-emitting devices, using the different treatment methods including solvent cleaning, hydrochloric acid treatment and oxygen plasma. The influence of modifications on the surface properties of ITO electrodes were investigated by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), contact angle, and four-point probe. The surface energies of the ITO substrates were also calculated from the measured contact angles. Experimental results demonstrate that the surface properties of the ITO substrates strongly depend on the modification methods, and oxygen plasma more effectively improves the ITO surface properties compared with the other treatments. Furthermore, the polymer light-emitting electrochemical cells (LECs) with the differently treated ITO substrates as device electrodes were fabricated and characterized. It is observed that the surface modifications on ITO electrodes have a certain degree of influence upon the injection current, luminance and efficiency, but hardly upon the turn-on voltages of current injection and light emission which are close to the measured energy gap of electroluminescent polymer. Oxygen plasma treatment on the ITO electrode yields the better performance of the LECs, due to the improvement of interface formation and electrical contact of the ITO electrode with the polymer blend in the LECs.     

Surface modifications of carbide ceramics induced by pulsed laser treatments

It is well known that sintered ceramics are very hard and difficult materials to process and machine by traditional methods. An easy and available solution seems to be a pulsed laser treatment, under appropriate experimental conditions (pulse duration and energy, radiation incidence angle, working atmospheres, etc.). In these experiments, in order to modify the structure and morphology of the surface, polycrystalline sintered SiC substrates were irradiated with an ArF (5=193 nm,h9=6.4 eV,F=30 ns) pulsed laser, at different fluences and at grazing incidence angle. Since it is well known that laser irradiation can produce both a dissociation of surface compounds and a high level of amorphisation (owing to very rapid cooling of melted material) different working atmospheres (Ar or O₂ or CH₄) and substrate heating (~700 °C) have been used, with the aim of confining and controlling any chemical and physical transformation produced by laser-material interaction. Morphological and structural modifications have been studied by SEM/EDAX microscopy. Surface chemistry has been analysed by Raman spectroscopy. Changes in surface roughness have also been quantified by AFM microscopy.     

Surface modifications of AISI 1045 steel created by high intensity 1064 and 532 nm picosecond Nd:YAG laser pulses

Interaction of Nd:YAG laser, operating at 1064 or 532 nm wavelength and a pulse duration of 40 ps, with AISI 1045 steel was studied. Surface damage thresholds were estimated to be 0.30 and 0.16 J/cm² at the wavelengths of 1064 and 532 nm, respectively. The steel surface modification was studied at the laser energy density of 10.3 J/cm² (at 1064 nm) and 5.4 J/cm² (at 532 nm). The energy absorbed from Nd:YAG laser beam is partially converted to thermal energy, which generates a series of effects, such as melting, vaporization of the molten material, shock waves, etc. The following AISI 1045 steel surface morphological changes and processes were observed: (i) both laser wavelengths cause damage of the steel in the central zone of irradiated area; (ii) appearance of a hydrodynamic feature in the form of resolidified droplets of the material in the surrounding outer zone with 1064 nm laser wavelength; (iii) appearance of periodic surface structures, at micro- and nano-level, with the 532 nm wavelength and, (iv) development of plasma in front of the target. Generally, interaction of laser beam with the AISI 1045 steel (at 1064 and 532 nm) results in a near-instantaneous creation of damage, meaning that large steel surfaces can be processed in short time.     

Surface modifications of ultra-thin gold films by swift heavy ion irradiation

Gold films of thickness 10 and 20 nm grown on float glass substrate by thermal evaporation technique were irradiated with 107 MeV Ag⁸⁺ and 58 MeV Ni⁵⁺ ions at different fluences and characterized by Grazing Incidence X-ray Diffraction (GIXRD) and Atomic Force Microscopy (AFM). The pristine films were continuous and no island structures were found even at these small thicknesses. The surface roughness estimated from AFM data did not show either monotonic increase or decrease with ion fluences. Instead, it increased at low fluences and decreased at high fluences for 20 nm thick film. In the 10 nm film roughness first increased with ion fluence, then decreased and again increased at higher fluences. The pattern of variation, however, was identical for Ni and Ag beams. Both the beams led to the formation of cracks on the film surface at intermediate fluences. The observed ion-irradiation induced thickness dependent topographic modification is explained by the spatial confinement of the energy deposited by ions in the reduced dimension of the films.     

Surface modifications of phosphated iron alloys: Influence on fatigue resistance

Zinc phosphating of Armco iron and a medium carbon steel with different solutions led to coatings that differed in morphology and phase composition. Not only the steel, but also the iron underwent a differential attack from the solutions, with a considerable increase in surface roughness. For the steel, particularly deep etching on ferrite areas caused a considerable reduction in the fatigue limit to rotating bending.     

Dynamic and fractal properties of SP-28 steel under high-speed loading conditions

Using an interferometric method to record the velocity of the free surface of a target subjected to two-dimensional shock loading, it is shown experimentally that the decrease in the compression pulse amplitude is due to the nonstationary nature of mesoscale processes — the amplitude decrease is progressively larger for higher rates of change of the variance of the mesoparticle velocity. It is shown theoretically that the loading rate influences the spallation strength of a material in a planar collision only if the variance of the particle velocity is nonzero. A fractal analysis of the spallation surfaces of steel samples is performed by quantitative fractography methods. An expression relating the fractal dimension of the spallation fracture surface and the variance of the mesoparticle velocity is derived. For typical values of the load pulse parameters for which back-side spallation occurs the fractal dimension agrees satisfactorily with the fractal dimensions for triadic Koch islands. Zh. Tekh. Fiz. 68, 43–49 (October 1998)     

Surface characterization of porous silicon after pore opening processes inducing chemical modifications

In this paper, we present a study on the porous silicon surface with the aim of filling porous silicon layers with organics. We discuss on two processes used to remove the outer parasitic layer created during the porous silicon formation. We demonstrate that these etching processes influences the surface properties, in particular wetting ability. By XPS and infrared absorption spectroscopy studies, we show that a SF₆ plasma treatment does not modify irreversibly the chemistry of porous silicon surface, nor the surface morphology. We also point out that NaOH etching does bring significant morphological modifications and influences the hydrophilicity of the porous silicon surface. This last treatment increases the polar groups (SiO) concentration on the pore surface and therefore allows a better filling of a porous silicon layer with organics, like dibromo-EDOT which can be thermally converted into PEDOT.     

Surface modifications of electrode materials for lithium-ion batteries: status and trends

The research on the electrodes of Li-ion batteries aims to increase the energy density and the power density, improve the calendar and the cycling life, without sacrificing the safety issues. A constant progress through the years has been obtained owing to the surface treatment of the particles, in particular the coating of the particles with a layer that protects the core region from side reactions with the electrolyte, prevents the loss of oxygen, and the dissolution of the metal ions in the electrolyte, or simply improve the conductivity of the powder. The purpose of the present work is to review the different surface modifications that have been tried in the past for the different electrodes that are currently commercialized, or considered as promising, including the three families of positive electrodes (lamellar, spinel, and olivine families) and the three negative electrodes (carbon, Li₄Ti₅O₁₂, and silicon). The role of the different coats used to improve either the surface conductivity, or the thermal stability, or the structural integrity is discussed. The limits in the efficiency of these different coats are also analyzed along with the understanding of the surface modifications that have been proposed.     

Mössbauer study of surface layers of high-speed steel after laser treatment

Mossbauer measurements in the backscattering geometry have been employed to determine an effect of the laser pulse duration on phase transformations and tungsten redistribution in the laser-affected area in the Tl high-speed steel. It has been found that after laser processing in the surface layer 10 μm thick the phase composition becomes homogeneous, the quantity of the retained austenite decreases with the rise in the laser pulse duration, the solid solution as a result of partial solution of carbides is saturated with tungsten up to 10 and 14 percent, the pulse durations being 1.2 and 6.0 ms respectively.     

Structure and topography modifications of austenitic steel surfaces after friction in sliding contact

Friction experiments between two austenitic stainless steel (AISI 304L) surfaces in sliding contact were carried out under very low loads in two liquid environments, namely demineralized water and methanol, in order to study the correlation between surface damage (wear and surface topography) and structural modifications (phase formation and microstructure). The particularity of our approach was to perform the tests under Hertzian pressures, which were several orders of magnitude lower than the elastic limit of stainless steel. The structural modifications produced during friction were analysed by X-ray diffraction and transmission electron microscopy and the surface topography was studied by scanning electron microscopy and three-dimensional (3D) profiling. Whatever the experimental conditions investigated, the morphology of the damage observed on both surfaces consisted of very fine, smooth and parallel grooves typical of an abrasive wear process of a ductile material caused by the ploughing action of hard particles. From the beginning of the tests, the transformation of austenite into martensite was observed in the superficial layers and the dominant presence of martensite was identified in the wear debris. These results suggest that, under our experimental conditions, abrasion is the dominant mechanism of material removal. Received: 12 March 2002 / Accepted: 3 May 2002 / Published online: 10 September 2002 RID="*" ID="*"Corresponding author. Fax: +33-5/4949-6692, E-mail: jean.paul.riviere@univ-poitiers.fr     

Absorption-free calibration on X-ray fluorescence analysis of high-speed steel with glass bead preparation

This article describes a novel idea on preparation of a glass bead for X-ray fluorescence spectrometry, to determine alloyed elements in high-speed steel without any matrix correction. The quantification method using the glass bead is generally effective to reduce secondary X-ray absorption and enhancement (matrix effect) by coexisting elements in a sample. Although the glass bead is normally prepared based on a flux-to-sample ratio, the suggested method mainly controls an absolute amount of the sample in the glass bead to prevent from any interference with the matrix elements. As a result, the alloyed elements, except tungsten, in high-speed steels could be determined with high precision and accuracy, independent of the flux-to-sample ratio. However, the fluorescent X-ray intensity of tungsten Lα line (8.40 keV) was obviously influenced by the sample amount (iron content) in a glass bead; in this case, the Mα line (1.77 keV) could be employed alternatively.