Effect of Pulsing Configuration and Magnetic Balance Degree on Mechanical Properties of CrN Coatings Deposited by Bipolar-HiPIMS onto Floating Substrate

Despite its great potential for thin films deposition and technological applications, the HiPIMS technology has its own limitations including the control of ion energy and flux towards the substrate when coping with the deposition of electrical insulating films and/or the deposition onto insulating/electrically grounded substrates. The bipolar-HiPIMS has been recently developed as a strategy to accelerate the plasma ions towards a growing film maintained at ground potential. In this work, the benefits of bipolar-HiPIMS deposition onto floating or nonconductive substrates are explored. The effect of bipolar-HIPIMS pulsing configuration, magnetic balance-unbalance degree, and substrate’s condition on plasma characteristics, microstructure evolution, and mechanical properties of CrN coatings was investigated. During the deposition with a balanced magnetron configuration, a significant ion bombardment effect was detected when short negative pulses and relative long positive pulses were used. XRD analysis and AFM observations revealed significant microstructural changes by increasing the positive pulse duration, which results in an increase in hardness from 7.3 to 16.2 GPa, during deposition on grounded substrates, and from 4.9 to 9.4 GPa during the deposition on floating substrates. The discrepancies between the hardness values of the films deposited on floating substrates and those of the films deposited on grounded substrates become smaller/larger when a type I/type II unbalanced magnetron configuration is used. Their hardness ratio was found to be 0.887, in the first case, and 0.393, in the second one. Advanced application-tailored coatings can be deposited onto floating substrates by using the bipolar-HiPIMS technology if short negative pulses, relative long positive pulses together with type I unbalanced magnetron are concomitantly used.

Thermal Stability of Silicon-Doped Tetrahedral Amorphous Diamond-Like Carbon Coatings And Improvement of Tribological Properties Through High- Temperature Annealing

We report the structure, mechanical properties, thermal stability, and durability of Si-doped tetrahedral amorphous carbon (Si-ta-C) coatings fabricated using simultaneous filtered cathodic vacuum arc deposition and direct current unbalanced magnetron sputtering. Si doping of 1.25–6.04 at.% was achieved by increasing the unbalanced magnetron sputtering power from 25 to 175 W. Si doping provided functionality to the coating, such as heat resistance, while retaining the high hardness of ta-C coatings. The Si-ta-C coatings were stable up to 600 °C regardless of the Si content, while the coating containing 3.85 at.% Si was stable up to 700 °C. The friction behavior and mechanical properties were dependent on the coating film before and after annealing at 100–200 °C; however, annealing at 300–400 °C decreased disk wear and increased counterpart wear due to an increase in film hardness on account of an endothermic reaction that increased the number of Si–C bonds. This indicates that the basic hardness characteristics of the ta-C coating and the high-temperature structural change of the Si-ta-C coating are important for ensuring high-temperature durability. These characteristics were verified through the low coefficient of friction and wear rate of the 1.25 at.% Si-ta-C coating after annealing at 500 °C.

Influence of Carbon: Metal Ratio on Tribological Behavior of Mo-W-C Coating

Mo-W-C coatings with three different C/(Mo+W) ratios (5:1, 2.8:1 and 2.2:1) were deposited by using combined unbalanced magnetron sputtering (UBMS) and high-power impulse magnetron sputtering (HIPIMS) technology. The influence of the C/(Mo+W) ratio on coating microstructure and related tribological properties at ambient temperature and at 200 °C were studied in lubricated condition (up to 7500 m and 1800 m of sliding distances, respectively). Results showed that a decrease in the C/(Mo+W) ratio could be correlated with an increase in coating thickness, adhesion strength, hardness and elastic modulus values, and a decrease in the degree of graphitization. At ambient temperature, outstanding tribological properties (very low friction and negligible wear) were observed irrespective of the C/(Mo+W) ratio. At 200 °C, low C/(Mo+W) ratios (2.8:1 and 2.2:1) were found particularly beneficial to achieve excellent tribological properties. The keys to significant friction reduction at 200 °C were (i) in situ formation of MoS2 and WS2 due to tribo-chemical reactions and (ii) presence of amorphous carbon debris particles in the protective tribolayer. With an increase in sliding distance, the tribolayer gradually lowered the friction coefficient by protecting both the coating and counterpart from severe wear. On the other hand, a high C/(Mo+W) ratio (5:1) led to low friction but noticeable abrasive wear at 200 °C.

Solar Coatings Based on Ag Infrared Reflector with High Stability at Medium and High Temperature

The manufacturing of thermally stable solar coatings with high photo-thermal performance represents a key factor for the further deployment of the CSP technology. Since 2005, ENEA has been developing solar coatings suitable for medium and high temperature applications based on the technology of double nitride cermet, by employing silver and tungsten as infrared reflectors, respectively. Thanks to the high infrared reflectance of silver, the corresponding coatings have better optical performance than those with tungsten; however, the high diffusivity of silver compromises its use at high temperature. In order to improve the structural and chemical stability at medium and high temperature of coatings based on silver, this infrared reflector was placed between compact and uniform layers of metal and cermet manufactured by using high-energy and fast deposition processes. In particular, an Unbalanced Magnetron cathode was adopted to promote an ion-assisted deposition process that improved uniformity and compactness of the metal and cermet films. The new coating shows no photo-thermal parameters degradation after 25 years of service at the operating temperature of 400 °C, while its photo-thermal conversion efficiency decreases by only 1.5% after 25 years of service at an operating temperature of 514 °C.

Impact Fretting Wear of MoS2/C Nanocomposite Coating with Different Carbon Contents under Cycling Low Kinetic Energy

MoS2/C nanocomposite coatings were deposited on a 304 stainless steel plate by unbalanced magnetron sputtering from carbon and molybdenum disulfide targets, and the target current of MoS2 was varied to prepare for coating with different carbon contents. The mechanical and tribological properties of the MoS2/C nanocomposite coating with different carbon contents were studied using a low-velocity impact wear machine based on kinetic energy control, and the substrate was used as the comparison material. The atomic content ratio of Mo to S in the MoS2/C coating prepared by unbalanced magnetron sputtering was approximately 1.3. The dynamic response and damage analysis revealed that the coating exhibited good impact wear resistance. Under the same experimental conditions, the wear depth of the MoS2/C coating was lower than that of the substrate, and the coating exhibited a different dynamic response process as the carbon content increased.

GAS DISTRIBUTION SYSTEM FOR OPTIMIZATION OF THE TECHNOLOGICAL PROCESS OF COATING IN AN UNBALANCED MAGNETRON SPUTTERING INSTALLATION

The paper proposes a new design solution for regulating the distribution of the working gases in the vacuum chamber of the installation (UDP -850/4) for unbalanced magnetron sputtering, which will improve the mode and quality of application of multilayer nano-coatings. Constructive documentation for manufacturing a gas distribution system has been prepared, as well as instructions for assembly to the vacuum chamber.

Characteristics of Palladium Doped Amorphous Carbon Films Fabricated by Unbalanced Magnetron Sputtering System

Generally, hydrogenated amorphous carbon (a-C:H) has been shown to have a low friction coefficient, high hardness, and low abrasive wear rate. In this study, Pd doped hydrogenated amorphous carbon (a-C:H:Pd) fabricated by the closed-field unbalanced magnetron sputtering (CFUBMS) system with two targets of carbon and palladium in Ar/C2H2 plasma. The tribological and lubricant characteristics for a-C:H:Pd fabricated with various DC bias voltage from 0 to −200 V were investigated. We obtained a hardness up to 27.5 GPa and friction coefficient lower than 0.1. The atomic percentage of Pd related to the lubricant properties increased up to 22% at −200 V. In the results, the Pd doping in the a-C:H films improved the tribological and lubricant properties. The friction coefficient value of a-C:H:Pd films was decreased, the hardness and elastic modulus were increased, and also the adhesion properties was improved with the increase of negative DC bias voltage.

A Comparative Assessment of Tribotechnical Characteristics of Solid Lubricant Coatings Deposited Using the Closed Field Unbalanced Magnetron Sputtering Ion Plating Technique for Various Operating Conditions

This paper presents a comparative assessment of the tribotechnical characteristics of friction pairs with solid lubricant coatings (SLC) based on the MoS2 suspension application of VNII NP 212 and SLCCFUBMSIP deposited by the closed field unbalanced magnetron sputter ion plating (CFUBMSIP) of combined compositions MoS2+Ti, MoS2+Zr, MoS2+Cr , MoS2+W. It was established that under normal atmospheric conditions in the friction modes corresponding to the contact friction temperature of 157 °С, the life of SLCCFUBMSIP was 42.1% higher, and the coefficient of friction (ffr) was on average 2 times lower than that of SLC VNII NP 212. The average value of the life reduction coefficient for SLCCFUBMSIP during the transition from normal atmospheric conditions to water was 2.98. Under normal atmospheric conditions and in water, the SLCCFUBMSIP coefficient of friction was in the range of 0.02–0.04, and in an oil environment it ranged from 0.03 to 0.08. SLCCFUBMSIP based on pure MoS2 in normal atmospheric conditions, in water and oil was practically unusable.