Effect of deposition pressure on microstructure and tribological behavior of MoS<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/MoS<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>-Mo nanoscale multi-layer films

MoS _x /MoS _x -Mo multi-layer films consisted of several bilayers and a surface layer on steel substrate were deposited by d.c. magnetron sputtering at different deposition pressures. Each bilayer contained a MoS _x layer with 80 nm in thickness and a MoS _x -Mo composite layer with 20 nm in thickness. With the increase of deposition pressure, the perpendicular orientation of the basal plane prevailed while the parallel orientation decreased. The tribological properties of the multi-layer films were investigated by using a ball-on-disk tribometer both in vacuum and in humid air. The multi-layer film deposited at 0.24 Pa had a compact, consistent layered structure with high intensity of (002) plane and low S content compared to the others deposited at 0.32 and 0.40 Pa, and showed the lowest friction coefficient and wear rate in humid air.     

Abrasive and Adhesive Wear Behavior of Arc-Evaporated Al<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Cr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>N Hard Coatings

During the last decade, the usage of difficult-to-machine materials such as austenitic stainless steels has increased continuously in various industrial applications. Tools such as blind hole taps, punches, or deep drawing molds are often exposed to severe wear while machining/forming these materials, mainly due to excessive adhesion and material transfer. On combination with abrasive wear due to work-hardened wear debris, tool lifetime in these applications is often limited. In this study, ball-on-disc experiments were carried out with arc-evaporated AlCrN coatings with different Al/(Al + Cr) ratios against Al₂O₃ and austenitic stainless steel balls in ambient atmosphere. Test temperatures of 25, 500, and 700°C were chosen for the hard Al₂O₃ balls simulating severe abrasive loads, whereas 25, 150, and 250°C were used for the softer stainless steel material to evaluate the adhesive wear behavior. Characterization of the wear tracks was done by scanning electron microscopy in combination with energy-dispersive X-ray analysis and optical profilometry. The best abrasive wear resistance during testing against Al₂O₃ was observed for the coating with the highest Al content. In the case of the austenitic stainless steel balls, sticking of the ball material to the coating surface was the dominating wear mechanism. The influence of test temperature, chemical composition, and surface roughness was studied in detail.     

Tribological Properties of Nanocomposite CrC<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/a-C:H Thin Films

Recently we showed that coatings, prepared by unbalanced magnetron sputtering from a metallic Cr target in an Ar/CH₄ discharge are composed of nanocrystalline CrC _x embedded in an a-C:H matrix. This work investigates the structural correlation of such nanocomposite CrC _x /a-C:H coatings to their tribological properties. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to characterize the phase composition and the chemical bonding in the films deposited at different experimental conditions. The coating microstructure was investigated on selected samples by high-resolution transmission electron microscopy. For CrC _x -dominated coatings deposited at CH₄ partial to total pressure ratios (p_CH4/p_t) < 0.42, only minor changes regarding the friction coefficients and the abrasive wear rates were observed although microstructural changes towards a higher degree of crystallinity were proven by transmission electron microscopy and substantiated with XPS results. For a-C:H dominated coatings deposited at p_CH4/p_t > 0.42, the friction coefficients and abrasive wear rates were shown to decrease with increasing a-C:H phase content and its more sp²-like bonding configuration. It can be concluded that the microstructural changes in terms of CrC _x crystallite coarsening and bonding configuration of the a-C:H matrix phase are responsible for the observed changes of the friction coefficients and wear rates.     

The Role of Configuration Entropy in Boundary Lubricants Based on the <Emphasis Type="Italic">n</Emphasis>-Perfluoropropylene Oxide Main Chain Structure

We have investigated the resistance of a novel end-functionalized perfluoropolyether (PFPE) lubricant film to slider–disk interactions caused by low-flying sliders. The PFPE lubricant is based on the CF₂CF₂CF₂O main chain monomer unit. Both slider–disk interactions and the formation of lubricant moguls are significantly reduced compared to the Fomblin Z backbone, (CF₂O) _p –(CF₂CF₂O) _q . These results are interpreted on the basis of ab initio quantum chemical computations that show that the barrier to internal rotation about the C–O bond in the CF₂CF₂CF₂O monomer unit is significantly larger than in the CF₂O monomer unit that is bordered by another CF₂O monomer unit, ~8 kcal/mol compared to <2 kcal/mol, respectively. It is proposed that main chains containing CF₂O monomer units will be very flexible and hence their physical properties will be more sensitive to adhesive and cohesive interactions, while main chains containing CF₂CF₂O and CF₂CF₂CF₂O monomer units will be comparatively stiffer and hence their physical properties will be less sensitive to adhesive and cohesive interactions.     

A Memetic Algorithm for the <Emphasis Type="SmallCaps">n</Emphasis>/2/Flowshop/α<Emphasis Type="SmallCaps">F </Emphasis>+ β<Emphasis Type="SmallCaps">C</Emphasis><Subscript>max</Subscript> Scheduling Problem

Machine scheduling has been a popular area of research during the past four decades. Its object is to determine the sequence for processing jobs on a given set of machines. The need for scheduling arises from the limited resources available to the decision-maker. In this study, a special situation involving a computationally difficult n/2/Flowshop/ αF + βCmax flowshop scheduling problem is discussed. We develop a memetic algorithm (MA, a hybrid genetic algorithm) by combining a genetic algorithm and the greedy heuristic using the pairwise exchange method and the insert method, to solve the n/2/Flowshop/ αF + βCmax flowshop scheduling problem. Preliminary computational experiments demonstrate the efficiency and performance of the proposed memetic algorithm. Our results compare favourably with the best-known branch-and-bound algorithm, the traditional genetic algorithm and the best-known heuristic algorithm.     

Aqueous Lubrication of SiC and Si<Subscript>3</Subscript>N<Subscript>4</Subscript> Ceramics Aided by a Brush-like Copolymer Additive,Poly(<Emphasis Type="SmallCaps">l</Emphasis>-lysine)-<Emphasis Type="Italic">graft</Emphasis>-poly(ethylene glycol)

We have examined the adsorption properties of poly(l-lysine)-graft-poly(ethylene glycol) (PLL-g-PEG)—a brush-like polymer—on Si₃N₄ and SiC surfaces and determined its impact on the aqueous lubrication of Si₃N₄ and SiC at various speeds and applied loads. The addition of PLL-g-PEG in aqueous solution reduces the interfacial friction forces significantly for self-mated sliding contacts of these two ceramics, as compared to lubrication with water or buffer solution alone. For SiC, the improved lubricating performance by addition of PLL-g-PEG was apparent for all tested speeds (from 1.4 to 185 mm/s under 2 N load). For Si₃N₄, the effect was more apparent in the slow-speed regime (≤20 mm/s under 2 N load) than in the high-speed regime (>100 mm/s), where extremely low coefficients of friction (μ ≤ 0.006) are readily achieved by aqueous buffer solution alone. It was further observed that the optimal lubricating effect with Si₃N₄ is achieved when the tribopairs are first run-in in polymer-free aqueous buffer to render the sliding surfaces smooth, after which the PLL-g-PEG copolymer is added to the buffer solution.     

Electron stimulated decomposition of fluorocarbons on amorphous hydrogenated carbon (<Emphasis Type="Italic">a</Emphasis>-CH<Subscript>x</Subscript>) overcoats used in data storage media

The electron-induced surface chemistry of perfluoropolyalkylether (PFPE) lubricants on a-CH_x films has been probed by studying the impact of free electrons on perfluorodiethylether, (CF₃CF₂)₂O, and 2,2,2-trifluoroethanol, CF₃CH₂OH, as models of the chemical functionality of PFPE lubricants such as Fomblin Zdol. Electron-stimulated decomposition of (CF₃CF₂)₂O and CF₃CH₂OH on fresh and oxidized a-CH_x is observed when the sample is unbiased and in the presence of 70 eV free electrons. Electron-induced decomposition is indicated by the deposition of fluorine onto the surface of the a-CH_x film following desorption of molecular (CF₃CF₂)₂O and CF₃CH₂OH by heating in front of a mass spectrometer. Biasing the sample to −80 V successfully eliminates the decomposition by preventing the impingement of electrons onto the surface. The electron-stimulated decomposition of PFPE lubricants may contribute to lubricant decomposition during normal drive operation.     

MoS<Subscript>2</Subscript> Films Formed by <Emphasis Type="Italic">In-contact</Emphasis> Decomposition of Water-soluble Tetraalkylammonium Thiomolybdates

Synthesis and tribological evaluation of three tetraalkylammonium thiomolybdate (R₄N)₂MoS₄ (R = methyl, propyl, or ammonia) aqueous-based lubricant additives on a ball-on-disk tribometer was carried out for a steel–aluminum contact. Tests were performed at the same conditions of load, entrainment speed, sliding distance, temperature, and concentration of MoS₂ to compare the activity (lubrication effect) of the thiomolybdates prepared. A friction reduction is observed for the three salts compared to pure water; however, significant differences in friction coefficient are observed depending on the alkyl group. SEM/EDAX and Raman analysis of the wear tracks reveal the in-contact formation of a MoS₂-lubricating film, rich in molybdenum and sulfur.     

Automatic discontinuous 2 × 1 transmission lines with sections of different productivity (q1 > q2), in the case of simultaneous failures of the sections and the bunker

An analytical solution is derived for automatic discontinuous 2 × 1 transmission lines with sections of different productivity (q ₁ > q ₂), in the case where simultaneous failures of the sections and the bunker are taken into account. The solution provides the basis for improvements in the design of such lines. The mathematical principles that have been developed evidently permit the analysis of any 2 × 1 transmission lines.     

Friction Force of Locust <Emphasis Type="Italic">Locusta migratoria manilensis</Emphasis> (Orthoptera,Locustidae) on Slippery Zones of Pitchers from Four <Emphasis Type="Italic">Nepenthes</Emphasis> Species

Slippery zone of inner pitchers in Nepenthes species serves functions of trapping insect and restraining escape of prey being used as a main nitrogen and phosphorus source. To investigate the influence of the slippery zones from different Nepenthes species on friction force of insect possessing smooth adhesive pads and rigid claws, friction force of locust Locusta migratoria manilensis on slippery surface of pitchers from four Nepenthes species was measured. The friction force of locust was also measured on stainless steel plate for comparison. Different friction forces were showed among the four Nepenthes species (mainly 380–550 mN in imagines, 120–185 mN in larvae), and were apparently lower than on the stainless steel plates (mainly 650 mN in imagines, 230 mN in larvae). Surface morphologies and structures of the slippery zones were observed and analyzed with scanning electron microscope and scanning white-light interferometer to explain the discrimination of the friction force. The slippery zones from the selected Nepenthes species exhibited similar surface morphologies and structures, but differed obviously in the geometrical dimensions of the surface architectures, and the difference probably result in the discriminations of the locust’s friction force. The obtained results contribute to further interpretation of the slippery zone’s anti-attachment mechanism to insect and presumably supply suitable theoretical foundations for biomimeticing structure and function of the slippery zone to develop slippery plates for trapping plague locusts or other agricultural pests.     

Plastic Scintillators Based on Polymethyl Methacrylate: <Emphasis Type="Italic">A Review</Emphasis>

The scintillation properties of plastic scintillators based on polymethyl methacrylate with various luminescent dyes are considered. It is shown that replacing the naphthalene conventionally used in these scintillators as a secondary solvent with octadeuteronaphthalene and 1,3-divinylbenzene will not alter either their scintillation efficiency and optical transparency, or their thermal, light, and radiation-damage stability; replacing it with 1,1,3-trimethyl-3-phenylindan, however, improves all these characteristics. It is demonstrated that n-terphenyl, 2,5-diphenyloxazole, 2-biphenyl-5-phenyl-1,3-oxazole, 2-biphenyl-(α-naphthyl)-1,3-oxazole, 2-phenyl-5-(4-biphenylyl)-1,3,4-oxadiazole, and 2-(4′-tret-butylphenyl)-5-(4″-biphenylyl)-1,3,4-oxadiazole can be used as luminescent activators, and n-bis-(o-methylstyryl)-benzene and 1,4-di-(5-phenyl-2-oxazolyl)-benzene are applicable as wavelength shifters.__________Translated from Pribory i Tekhnika Eksperimenta, No. 3, 2005, pp. 5–15.Original Russian Text Copyright © 2005 by Salimgareeva, Kolesov.     

Modeling the formation of silicon nanoclusters during annealing SiO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> layers

The mechanism of formation of silicon nanoclusters in layers of nonstoichiometric composition is studied by Monte Carlo simulation. Interest in silicon nanoclusters (Si-nc) coated with an oxide layer is due to their applications in modern optoelectronics and nanoelectronics. A lattice Monte Carlo model is proposed to study atomic processes in the Si-SiO₂ system. The formation of silicon nanoclusters during annealing of single SiO layers and SiO₂-SiO-SiO₂ layered structures is studied. Along with the diffusive motion of particles, the model takes into account the formation and collapse of mobile molecules of silicon monoxide. It is shown that accounting for transport of silicon under high-temperature annealing due to the motion of SiO accelerates the formation of Si-nc. Dependences of the size of nanoclusters on temperature, annealing time, and the composition of the SiO _x layer are obtained. It is found that annealing of silica films containing layers of nonstoichiometric composition can lead to the formation of silicon nanoclusters or cavities.     

Friction and wear properties of CN<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/SiC in water lubrication

Amorphous carbon nitride coatings (a-CN_x) were deposited on SiC disk by ion beam assisted deposition (IBAD). The tribological behavior of a-CN_x coating sliding against SiC ball in water was investigated and compared with that of SiC/SiC system at room temperature. The influences of testing conditions on friction coefficient and specific wear rate of both kinds of tribopairs were studied. The worn surfaces on disks were observed by scanning electron microscope (SEM). The results indicate that the running-in period of a-CN_x/SiC was shorter than that of SiC/SiC system in water. At a sliding velocity of 120 mm/s, the mean steady-state friction coefficients of SiC/SiC (0.096) was higher than that of a-CN_x/SiC (0.05), while at 160 mm/s, lower friction coefficient (0.01) was obtained for SiC/SiC in water. With an increment of normal load, the mean steady-state friction coefficients after running-in first decreased, reaching a minimum value, and then increased. For self-mated SiC, the specific wear rate of SiC ball was a little higher than that of SiC disk, while for a-CN_x/SiC, the specific wear rate of SiC ball were 10 times smaller than that of a-CN_x coating. Furthermore, the specific wear rate of SiC ball sliding against a-CN_x coating was reduced by a factor up to 100~1000 in comparison to that against SiC in water. The wear mechanism of SiC/SiC system in water is related to micro-fracture of ceramic and instability of tribochemical reaction layer. Conversely, wear mechanism for a-CN_x/SiC is related to formation and transfer of easy-shear friction layer.     

Synthesis of gear transmissions with arbitrary <Emphasis Type="Italic">n</Emphasis>-pair engagement

The synthesis of gear transmissions with arbitrary n-pair tooth contact is considered (n is any integer greater than two). Multipair engagement is the result of height and profile modification of the teeth, by adjustment and shift of the initial contour. Formulas for force and strength analysis of multipair transmissions are presented. Examples outline the synthesis of transmissions with engagement at three, four, or more pairs, in any working range of the number of teeth. The benefits of multipair engagement are illustrated by sample calculations of a tooth pair in single-pair and multipair engagement.     

Photoconductivity in a magnetic field and photomagnetic effect in <Emphasis Type="Italic">p</Emphasis>-HgCdTe graded-gap photodetecting film structures

The photomagnetic effect and photoconductivity in a magnetic field are studied at a liquid nitrogen temperature for the Voigt geometry on p-HgCdTe films with graded-gap boundary regions where the content of cadmium (x) is increased above its mole fraction in the central area of the structure with a uniform distribution of x. A case with dominating Shockley-Read recombination is considered. It is demonstrated on the basis of experimental data that the film structure in studying these effects can be replaced by the central area with an identical value of x, by introducing effective velocities of surface recombination and surface generation of excess charge carriers on the interfaces between the central area and the graded-gap regions.     

Poly-<Emphasis Type="Italic">p</Emphasis>-phenyl sulfide as the material for oil-lubricated sliding bearings

Tribological analysis of two different poly-p-phenyl sulfides, with melt viscosity differing more than twofold, is performed. The tribological properties of the poly-p-phenyl sulfides are compared with those of the composites based on minced carbofibers with 0.5% of fullerene C₆₀ by mass added into the matrix of the composites. In interpreting the tribological dependences it is especially noteworthy that the load-bearing capacity of the materials allows consideration of many of these dependences as phase diagrams.     

Nonparametric estimation of a density and its derivatives: The <Emphasis Type="Italic">L</Emphasis><Subscript>2</Subscript>-approach

The nonparametric estimates of a density and its derivatives are considered within the scope of the L ₂-approach. New sets of weight functions with a bounded support are proposed for constructing admissible (unimprovable in the space metric L ₂(?∞, ∞)) estimates of the density itself and its derivatives to the third order, inclusive.     

Determining the constants of integration for automatic lines with determinate processes

In the study of automated lines, a method is proposed for determining the constants of integration in the case of the general solution when the productivities of different sections of the line are unequal (q ₁ > q ₂ or q ₁ < q ₂) and the particular solution when q ₁ = q ₂. This method provides the basis for the solution of all problems regarding 2 × 1 automatic lines with deterministic processes.     

Physical interpretation of the <Emphasis Type="Italic">J</Emphasis><Subscript>2</Subscript> integral by identifying the associated crack translation

The physical interpretation of the J integral (i.e., J ₁ integral) is clear. J ₁ integral is the energy release rate associated with crack extension (i.e., translation of the crack in the x ₁ direction). However, the physical interpretation of the J ₂ integral remains unclear. In this study, different crack translations in the x ₂ direction were selected and tested by calculating the energy release rates associated with the crack translations and comparing them with the theoretical value of the J ₂ integral.     

Substrate dependence of the scratch resistance of CrN<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> coatings on steel

Hard CrN_x coatings were sputter deposited on hot work tool steel (HWTS) and high speed steel (HSS) in an industrial PVD reactor. Coatings were deposited under various nitrogen flows. The thickness, density, hardness, elastic modulus, composition, and stress were determined for the coatings. The specimens were subjected to scratch testing. Two different failure mechanisms were investigated: chipping and complete coating removal. For all specimens, the coating-to-substrate adhesion was that good that adhesion did not limit the scratch resistance. Therefore, the minimum loads at which a given type of failure was initiated were not a measure for the coating-to-substrate adhesion. The scratch resistance was better for coatings on HSS than for coatings on HWTS. This is due to the higher hardness of the HSS. Substrate independent measures for the scratch resistance of the coating were obtained by considering critical track widths instead of critical loads. The hardening of the coating--substrate systems due to the coating was investigated. The uncoated substrates exhibited track width independent scratch hardness. For the coated specimens the scratch hardness increased with increasing track width until chipping of the coating occurred. Complete coating removal coincided with a decrease in hardness. Although the elastic properties, hardness, and thickness of all coatings were more or less equal, CrN_1.0 coatings outperformed CrN_0.6 coatings in scratch tests both on HSS and on HWTS.