Grudinin, V. A.Bleykher, G. A.Sidelev, D., VYuriev, Yu N....
11页
查看更多>>摘要：The article focuses on some formation peculiarities of chromium nitride coatings in an argon and nitrogen atmosphere during the magnetron sputtering of a hot chromium target enhanced by a radio-frequency source of inductively-coupled plasma. In the work, the dependence of the deposition rate of coatings on the magnetron power density has been defined, and the contribution of sublimation to deposition rate enhancement has been examined in comparison with conventional sputtering of a cooled target. It has been shown that the dependence of the deposition rate on the magnetron power density is a nonlinearly increasing function of over 18 W/cm(2). By experiments and calculations, it has been proven that in the range from 18 to 28 W/cm(2) the target sublimation enables an increase in the deposition productivity by a factor from 2 to 12 compared with the cooled target sputtering under the same experimental conditions. For example, in the regime of planetary rotation of the substrates, the deposition rate reaches 5.2 nm/s at 28 W/cm(2). The elemental and structural-phase composition of the coatings deposited using the planetary rotation of substrates has been studied depending on a magnetron power density. It has been found that with an intense sublimation on the chromium target surface, the coatings have an inhomogeneous elemental and structural-phase composition. In addition, an alternation of chromium layers with a low content of chromium nitride and layers that mainly consist of chromium nitride has been determined.
查看更多>>摘要：Crystalline-to-amorphous transitions induced by chemical modulation have been attracting great research interests and an in-depth understanding of such transitions is always demanding. Here we design the Nb-Ti-Zr-(Si) alloy systems employing the empirical criteria and the related phase diagrams for enhancing mechanical properties accompanied by Si-induced microstructure evolutions. (NbTiZr)(100-x)Si-x (x = 0, 3.0, 10.2, 22.2, and 25.0 at.%) refractory medium-entropy alloy (RMEA) coatings are synthesized by magnetron co-sputtering. With increasing Si content, the pristine body-centered cubic (bcc) single phase transforms into a nanocomposite structure consisting of bcc nanocrystals embedded in an amorphous matrix and eventually into an entirely amorphous structure. This is well rationalized with a thermodynamic database of the Nb-Ti-Zr-Si system constructed using the CALPHAD (CALculation of PHAse Diagrams) approach, which suggests the bcc structure to be thermodynamically stable at low Si contents and the formation of amorphous RMEA to be preferred at higher Si contents. The superior mechanical property of the amorphous (NbTiZr)(75.0)Si-25.0 (at.%) coating compared to the Si-free counterpart is achieved, i.e., the hardness (H) increases by 115% and the elastic modulus (E) increases by 70%. The Si-induced crystalline-to-amorphous transition in RMEA which leads to a consistently impressive strengthening effect was rarely found in other alloys or coatings.
查看更多>>摘要：Amorphous boron carbide (B4C) thin films are by far the most popular form for the neutron converting layers in the 10B-based neutron detectors, which are a rising trend in detector technologies in response to the increasing scarcity and price of( 3)He, the standard material for neutron detection. The microstructure of the B4C films is closely related to the important properties, e.g. density and adhesion, for the converting layers, which eventually affect the detection efficiency and the long-term stability of the detectors. To study the influence from substrates of different roughness and materials, the B4C films were deposited on polished Si substrates with Al, Ti, and Cu buffer layers and unpolished Si, Al, Ti, and Cu substrates by direct current magnetron sputtering at a substrate temperature of 623 K. The tapered columnar grains and nodular defects, generally observed in SEM images, indicated a strong shadowing effect where voids were introduced around the grains. The change in the grain size did not show a direct dependence to the substrate roughness, acquired from the surface profile, nor to the mass density of the films, obtained from reflectivity patterns. However, films with non-uniform size of columnar grains were deposited on substrates with high skewness, leading to a drop of mass density from-95% down to-70% of tabulated bulk density. On the other hand, similar microstructures and mass density were obtained from the films deposited on Al, Ti, and Cu of different roughness and good adhesion were observed from cross-cut adhesion tests, showing the reliability of sputtering deposited B4C films on common structural materials in neutron detectors.
查看更多>>摘要：Molybdenum disulfide (MoS2) is used extensively in aerospace applications, where liquid lubricants are not suitable. MoS2 has excellent tribological properties in vacuum, however, further research is required to fully understand the mechanisms taking place when exposed to varying temperatures in ambient atmosphere due to storage and on-ground testing. MoS2 coatings were deposited on AISI 440C steel substrates, friction and wear tests were conducted at increasing temperatures, up to 75 ?degrees C, determining the effect of temperature on wear mechanisms in air. It was found that the detected surface oxides do not impact tribological properties in MoS2 at temperatures around 75 ?degrees C. The water molecules at room temperature hinder the alignment of MoS2 layers leaving some active edge sites exposed to contacting surfaces, leading to high friction and wear. Desorption of water molecules promote parallel alignment of layers, reducing shear strength, friction and wear.
Sidelev, D., VPoltronieri, C.Bestetti, M.Krinitcyn, M. G....
13页
查看更多>>摘要：Chromium coatings were deposited either by magnetron sputtering and electroplating on E110 zirconium alloy. The as-deposited Cr coatings showed dense microstructure, but different mechanical properties and adhesion behavior depending on the deposition technology. High-temperature oxidation was performed in air at 1100 C for 40 min. The magnetron-deposited coatings had a stable oxidation behavior which was improved by increasing coating thickness. Surface activation of E110 alloy prior to Cr electroplating resulted in formation of the interlayer with a thickness of 7-12 mu m between the coating and the alloy containing hydride and fluoride phases. It was shown that cracks and defects in this interlayer of the electroplated Cr coatings affected the coating adhesion and resulted in lower oxidation resistance compared to the magnetron-deposited coatings.
查看更多>>摘要：The present study estimates the corrosion and wetting properties of sputter deposited osbornite titanium nitride (O-TiN) coating onto a stainless steel (SS-304). The wettability, surface morphology, chemical composition and corrosion characteristics of the treated samples were studied in detail. The performances of the O-TiN@SS-304 coating were compared to polished SS-304 substrate. The results show that the nano-cluster growth of O-TiN coating alter the hydrophilic surface (theta(w) similar to 78.2 degrees) of SS-304 into hydrophobic surface (95.41, which promote the aqueous passivation behavior. The corrosion testing for a long-term immersion (6 h) illustrated that the coated sample shows greater corrosion resistance than the SS-304. This greater corrosion resistance is accountable for low degree of corrosion rate of around 16.7 x 10(-3) mm/year of the coated sample. Therefore, the O-TiN nanocluster coating with a homogeneously ordered hydrophobic surface is projected as a long-lasting, stable and corrosion resistive for industries, when immersed in salinity media [3.5% NaCl] and useful for extending the protecting applications in other relevant material fields.
查看更多>>摘要：To analyze the formation mechanism of a dark streaky edge defect on a hot-dip galvannealed (GA) ultra-high strength steel (UHSS) sheet, multiple metallographic characterizations were performed on samples collected from different processes. It was found that this streaky defect was directly caused by differences in the coating morphology. The coating in the edge zone showed a crater morphology, while the coating in the center zone showed a flatter morphology and uniform coating thickness. Corresponding streaky edge defects were found on the annealed steel prior to hot-dipping and on the pickled steel prior to cold rolling. The root cause was finally traced back to the hot-rolled steel after coiling. A formation mechanism of this defect was proposed based on the evolution of surface microstructures in multiple processes. The difference in the amounts of internal oxides formed in the subsurface of different zones of the hot-rolled strip influenced the pickled steel surface, cold-rolled steel surface, annealed steel surface and the galvannealed coating surface.
查看更多>>摘要：In this work, a photospectrometric method was used to quantify chromium evaporation from the AISI 441 ferritic stainless steel. Experiments were conducted for 250 h in the temperature range of 650-850 degrees C to evaluate the time and temperature dependence of chromium evaporation in the initial oxidation stage. The results showed a thermally activated process with an activation energy of 218.3 kJ.mol(- 1) and parabolic evolution over time at 650 and 750 degrees C, while a change in the evaporation kinetics was observed at 850 degrees C, resulting in a linear trend. A diffusion-evaporation model was applied and compared to the experimental data demonstrating the role of the chromium cation diffusion on the evaporation process.
Alves, S. A.Fernandez-Lopez, P.Lopez-Ortega, A.Fernandez, X....
18页
查看更多>>摘要：Aluminum-silicon (Al-Si) alloys have been increasingly used in several industries to develop novel lighter and high-performance components. Nevertheless, these novel advanced materials display poor wear resistance which hamper their application in several critical tribological components. This investigation is focused on the surface modification of Al-Si alloys with high Si content, through a breakthrough green coating technology named plasma electrolytic oxidation (PEO). The main aim is, for the first time, to study the tribological behavior of PEO-treated cylinder liners made of cast Al with high Si content, in a configuration mimicking the real contact between a cylinder liner and a piston ring. Additionally, this study is based on the development of a novel electrolyte especially designed to generate PEO films with improved tribological properties.& nbsp;Novel films were successfully synthesized by PEO in an innovative aluminate-based electrolyte. The morphological, topographical, and chemical features of the films were assessed through scanning electron microscopy (SEM), thickness and average roughness (R-a) measurements, energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). Cross-sectional SEM images showed that PEO films developed in the novel electrolyte are denser and thicker. Additionally, the novel PEO-treated cylinder liners, presented a significantly improved resistance to wear damage when submitted to tribological actions simulating the cylinder liner/piston ring real contact movements, which was linked with the extremely higher hardness of the films. These cylinder liners presented a lower COF compared to the commercial reference, along the whole duration of sliding. Finally, tribological tests showed that PEO-treated Al cylinder liners displayed a similar level of mechanical wear damage that steel cylinder liners.& nbsp;The results presented in this investigation envisage the feasibility of PEO to be applied on Al-Si engine components submitted to aggressive tribological conditions, enhancing their durability requirements to levels similar to components made of steel.
查看更多>>摘要：Corrosion protection of magnesium alloys is a challenge in industrial applications because of the high chemical reactivity of Mg. In this work, a coating is prepared by plasma electrolytic oxidation (PEO) on the AZ31B Mg alloy and then modified by insoluble zinc phosphate to improve the corrosion resistance. To avoid the influence of the weak acidic Zn-containing electrolyte on the formation of the passivation layer on the magnesium alloy, a two-step process is designed to first produce a passivation layer before introduction of zinc phosphate. Zinc phosphate is mainly distributed on the surface and the sidewalls of the holes in the porous coating and blocks the interactions between the corrosive solution and Mg substrate. The corrosion potential of the optimal coating (Zn-15) increase while the passive current density at the terminal potential decreases, suggesting the significantly improved corrosion resistance compared to the pristine AZ31B. The life time demonstrated by neutral salt spraying is 4200 h that is about 3 times longer than that observed from the Mg alloy with the undoped coating.
NSTL
Elsevier