TEM investigation of MoSeC films

Transition metal dichalcogenides (TMD) are widely used as self-lubricating material either as oil additive or directly as thin films. Magnetron sputtering is a deposition method allowing depositing such films with high density and adhesion. However, their spread use in practical applications is still hindered since their excellent sliding properties are deteriorated in the presence of humidity and under high contact pressures. MoSe2, one of the members of TMD family recently studied, has been co-sputtered with carbon in order to improve the mechanical and tribological properties when compared to pure MoSe2 film

Electrochemical corrosion of magnetron sputtered WTiN-coated mild steels in a chloride medium

The electrochemical corrosion behaviour of WTiN coatings, of composition W 31, Ti 28 and N 40 at.% sputtered on carbon steel, chromium steel and high speed steel (HSS) has been investigated and the effect of the steel heat treatment on the steel/WTiN system performance explored. Open circuit potential measurements, polarisation curves and electrochemical impedance spectroscopy were used, together with X-ray diffraction and scanning electron microscopy to characterise the corroded and uncorroded coating/substrate systems. It was found that the influence of the substrate on corrosion resistance follows the order Carbon Steel<HSS<Chromium Steel. The best performance of the chromium steel/WTiN system can be associated with the higher compactness of the protective coating, since there is strong evidence that it is inert so that electrolyte penetration through the coating defects and pores is responsible for the initiation of substrate corrosion. Heat treatment of the substrate has some influence on the corrosion of the HSS/coating system, suggesting that there may be one ideal steel treatment temperature for which the coating adhesion is higher.http://www.sciencedirect.com/science/article/B6TVV-473F2MV-S/1/91525d9a77234a2d57d1825d9d68d1b

FELINE: Finite element solver for hydrodynamic lubrication problems using the inexact Newton method

In this work we present FELINE, a C++ solver of the Reynolds equation for treating hydrodynamic lubrication problems. To correctly describe cavitation regions, FELINE implements the inexact Newton iteration (INE) algorithm within a finite element method (FEM) framework. The solver was tested and validated against known cases in literature and industrially relevant cases of dimpled textures. Furthermore, we provide a benchmark for a complex dimpled texture case to evaluate the performance and robustness of the implementation. FELINE performs very fast when compared with existing implementations and shows a great degree of stability, while providing physically correct solutions thanks to the INE algorithm.This work was supported by the Portuguese Foundation for Science and Technology (in the framework of the Strategic Funding UIDB/04650/2020 project PTDC/EME-SIS/30446/2017 and Advanced Computing Project CPCA/A2/ 4513/2020, awarded by FCT I.P., for accessing MACC-BOB HPC resources

From Ti–Al- to Ti–Al–N-sputtered 2D materials

Abstract This paper reviews thin films constituted by elements based on the Ti–Al–N system, bearing in mind the role of the condensed phases in the development of structural components and functional devices. In recent decades, the Ti–Al, Ti–N and Al–N nanocrystalline binary systems have rapidly attracted research and industry interest. These systems have revealed a great performance via atomic-level structural control, making it possible to tailor new atomic structures and morphologies suitable in different applications as protective and hard coatings and as thermal/diffusion barriers. The binary phases based on nitrogen were the first to exhibit a wealth of interesting mechanical and electrochemical behaviours. However, more recently the Ti-Al and, particularly, the Ti1 - x Al x N thin films have been applied with success in the industry. The purpose of this paper is to compile the master results concerning the production and characterisation of binary and ternary thin films of the Ti–Al–N system using similar deposition strategies. These materials form a good base to analyse the correlation between the chemical composition and the atomic structure, the preferred orientations and the morphology of 2D monolithic materials. The deposition strategies adopted and the thin films’ chemical compositions determine the as-deposited structures and, consequently, the mechanical behaviour of the thin films produced, particularly the hardness. In general, an intermediary amorphous stage is observed, i.e., the thin films exhibit a loss of crystallinity in the transition from a saturated solid solution to a new compound

A deep learning approach to the texture optimization problem for friction control in lubricated contacts

The possibility to control friction through surface micro texturing could offer invaluable advantages in many fields, from wear and pollution reduction in the transportation industry to improved adhesion and grip. Unfortunately, the texture optimization problem is very hard to solve using traditional experimental and numerical methods, due to the complexity of the texture configuration space. In this work, we apply machine learning techniques to perform the texture optimization, by training a deep neural network to predict, with extremely high accuracy and speed, the Stribeck curve of a textured surface in lubricated contact. The deep neural network was used to completely resolve the mapping between textures and Stribeck curves, enabling a simple method to solve the texture optimization problem. This work demonstrates the potential of machine learning techniques in texture optimization for friction control in lubricated contacts

Deep learning approach to the texture optimization problem for friction control in lubricated contacts

All the data used in this work is available free of charge from https://doi.org/10.34622/datarepositorium/MUVOJDThe possibility to control friction through surface microtexturing can offer invaluable advantages in many fields, from wear and pollution reduction in the transportation industry to improved adhesion and grip. Unfortunately, the texture optimization problem is very hard to solve using traditional experimental and numerical methods, due to the complexity of the texture configuration space. Here, we apply machine learning techniques to perform the texture optimization, by training a deep neural network to predict, with extremely high accuracy and speed, the Stribeck curve of a textured surface in lubricated contact. The deep neural network is used to completely resolve the mapping between textures and Stribeck curves, enabling a simple method to solve the texture optimization problem. This work demonstrates the potential of machine learning techniques in texture optimization for friction control in lubricated contacts.This work was supported by the Portuguese Foundation for Science and Technology (FCT, I.P.) in the framework of the Strategic Funding UIDB/04650/2020, projects PTDC/EME-SIS/30446/2017, project POCI-01–0247-FEDER-045940, and Advanced Computing Project CPCA/A2/4513/2020 for accessing MACC-BOB HPC resources

Effect of Annealing Heat Treatment on the Composition, Morphology, Structure and Mechanical Properties of the W-S-N Coatings

Alloyed-transition metal dichalcogenide (TMD) coatings have been under investigation as multi-environment lubricants for the past few decades. These coatings display very low coefficient of friction properties at elevated temperatures. Studies on the annealing of these low-friction coatings are missing in the literature. For the first time, in this study, the annealing of the W-S-N dry lubricant coatings was carried out to study its effects on the composition, morphology, crystal structure and hardness of the coatings. The W-S-N coatings were deposited by direct current (DC) reactive magnetron sputtering. The analysis was carried out for as-deposited, 200 °C and 400 °C annealed coatings. The as-deposited coatings have N content in the range of 0–25.5 at. %. The coatings are compact and the densification increased with the increase in N-alloying. All the coatings are crystalline except the highest N-alloyed coating which is X-ray amorphous. A maximum hardness of 8.0 GPa was measured for the coating alloyed with 23 at. % N. Annealing did not affect the composition and morphology of the coatings, while some variations were observed in their crystal structure and hardness. The maximum hardness increased from 8 GPa to 9.2 GPa after 400 °C annealing of the 23 at. % N-alloyed coating.This study is sponsored by FEDER National funds FCT under the projects: SMARTLUB ref.“POCI-01-0145-FEDER-031807”, CEMMPRE ref. “UIDB/00285/2020”, On-SURF ref. “POCI-01-0247-FEDER-024521”, “LA/P/0112/2020” and Atrito-0 ref. “POCI-01-0145-FEDER-030446”.info:eu-repo/semantics/publishedVersio

Vacuum Tribological Properties of W-S-N Coatings Synthesized by Direct Current Magnetron Sputtering

This work deals with the investigation of the tribological performance of DC magnetron sputteredW-S-N coatings under vacuum atmosphere, as part of the exploration of multi-environment sliding properties of W-S-N solid lubricants. This study is part of the systematic testing of W-S-N solid lubricants in different environments, especially vacuum, which is often ignored. The trend is to test sliding properties in dry N2 by considering it as replacement of vacuum environment testing. This approach is not appropriate. In this work, a set of coatings was synthesized with N-alloying content in the range of 0–25.5 at.%. A maximum S/W ratio of 1.47 was observed for the pure WSx coating. A maximum hardness of 8.0 GPa was observed for 23 at.% of N-alloying. The coating with the lowest N content (14.6 at.%) displayed the lowest friction, specific wear rate and wear scar depth under vacuum conditions. Despite superior sliding performance at room temperature (35% humidity), 200 C and dry nitrogen conditions, the performance of the WSN12.5 coating deteriorated vacuum environment.This work is sponsored by FEDER National funds FCT under the projects: SMARTLUB ref. “POCI-01-0145-FEDER-031807”, CEMMPRE ref. “UIDB/00285/2020”, On-SURF ref. “POCI-01-0247- FEDER-024521”, “LA/P/0112/2020” and Atrito-0 ref. “POCI-01-0145-FEDER-030446”. Andrey Bondarev acknowledges the support of the project “International Mobility of the scientific workers MSCAIF IV at Czech Technical University in Prague, Grant No: CZ.02.2.69/0.0/0.0/20_079/0017983”.info:eu-repo/semantics/publishedVersio

Influence of laser structural patterning on the tribological performance of C-alloyed W-S coatings

In this paper, we are proposing for the first time the partial laser treatment of a self-lubricating coating in order to optimize its frictional performance from the very first moments of the sliding contact. W-S films alloyed with carbon were deposited by closed field unbalanced magnetron sputtering. The coatings were treated using two types of lasers, with peak emissions in the UV and IR, under different laser power conditions and patterning. The structure, mechanical and tribological properties of the treated coatings were analysed using X-ray diffraction (XRD), Raman spectroscopy, nanoindentation and reciprocating ball-on-disk tribometry. Although XRD diffractograms illustrated an overall amorphous structure in all as-deposited and treated samples, their Raman spectra confirmed the presence of WS2 crystalline phase in some of the treated areas. Furthermore, in the samples where WS2 Raman peaks were detected, the friction coefficient was in the initial part of the test lower than that of untreated coating. Previous crystallization of the W-S phase before tribological testing has a key role for shortening the self-adaption process improving the overall friction performance of the coatings.publishe

Optical properties and refractive index sensitivity of reactive sputtered oxide coatings with embedded Au clusters

The following article appeared in Journal of Applied Physics 115.6 (2014): 063512 and may be found at http://scitation.aip.org/content/aip/journal/jap/115/6/10.1063/1.4861136In the present study, nanocomposite coatings of Au clusters embedded in two different oxides, TiO2 and Al2O3, were synthesized using pulsed DC magnetron sputtering. The depositions were carried out in three steps, by depositing the oxide, the Au clusters, and again the oxide. The deposition time of the Au clusters was varied in order to achieve different cluster sizes, morphologies, and nanocomposite topographies. The structure, microstructure, morphology, and the optical properties of the coatings were studied. With the increase in Au content, red-shifted surface plasmon resonance (SPR) peaks with higher intensity and increased widths were observed due to changes in the metal clusters sizes and morphology and due to interparticle effects. In order to relate the peculiar SPR extinction bands with the different clusters shapes and distributions, a simulation of the optical properties of the nanocomposites was performed making use of the Renormalized Maxwell-Garnett approach. A theoretical study concerning the refractive index sensitivity was made in order to predict the optimal coatings parameters for sensing experiments. The increased surface area and the strong SPR extinction bands make these coatings suitable for gas sensing and also catalysis, albeit many other application fields can be envisaged.This research was sponsored by FEDER funds through the program COMPETE, Programa Operacional Factores de Competitividade, by national funds through FCT, Fundacao para a Ciencia e a Tecnologia, under the Projects PEst-C/EME/UI0285/2013 and CENTRO-07-0224-FEDER-002001 (Mais Centro SCT_2011_02_001_4637), and through the Spanish Ministry of Science and Innovation by Projects FUNCOAT CSD2008-00023 and AIB2010PT-00241. R.E.G. wishes also to thank the MCINN for the financial support within the Ramón y Cajal programme. Funding by the European Community through Project Nano4Color is gratefully acknowledged