Deposition Of Coatings Research Articles

Investigation of high entropy alloy coatings produced by electrical discharge machining

The exploration of High Entropy Alloys (HEAs) has attracted significant attention due to their multifaceted property profile, suitable for a diverse range of industrial applications. Traditional fabrication techniques, such as melting, have been met with efficiency constraints, necessitating the investigation of alternative approaches for HEA development. The present study examines the feasibility of Electrical Discharge Coating (EDC) as a new and alternative process for the potentially cost-effective fabrication of HEA coatings, with an emphasis on enhancing surface integrity. To provide empirical insights, the research focuses on the deposition of HEA coatings on substrates of X37CrMoV5-1 steel and aluminum, utilizing powder electrodes made of Fe-Co-Mn-Ni-Cr and Fe-Co-Mn-Ni-Cu. The influence of Electrical Discharge Coating (EDC) process parameters on the formation and quality of the High Entropy Alloy (HEA) coatings was evaluated by advanced microstructural characterization techniques. The results show that HEA coatings could be fabricated using EDC, achieving a coating thickness of more than 40 µm.

On the Polymeric Coating Deposition Techniques to Increase Body Acceptance and Allow Drug Delivery in Smart Bio-devices

Currently, prosthetic devices have been significantly improved thanks to highly biocompatible metallic alloys, such as titanium alloys, and owing to the use of antibiotic treatments to allow higher acceptance of the implant. However, risks of infection or implants collapse are always possible since the human body recognizes prosthetic devices as foreign bodies and reacts to them accordingly. The surface of a prosthetic device guides the first interactions with the surrounding environment, and thus the necessity to act on the prosthesis surface with a local approach arises. Indeed, the creation of surface coatings that can potentially be loaded to perform local drug delivery represents a way to reduce systemic antibiotic delivery while improving body tolerance to the implanted devices. Within this framework, the current study aims to investigate the influence of different techniques applied to produce polymer-based coatings upon titanium alloy bio-devices, with the purpose of optimizing their durability. Specifically, the experimental campaign examined three different coating techniques (electrophoretic deposition, dip coating, and spray coating), to compare the results in terms of coating uniformity and mechanical adhesion to the titanium alloy.

Substrate surface processing in gas vacuum arc discharge

Problem. Preparation of the surface before the deposition of vacuum arc coatings is of great importance, as it affects not only the adhesive properties of the obtained coatings, but also the physical and mechanical properties of the substrate surface layer. The processes of ions interaction with the substrate surface during its ionic cleaning, before the deposition of coatings, have been relatively little studied and are almost not described in the literature. Goal. In this work, some of their features are considered in relation to the surface preparation of materials before the deposition of vacuum arc coatings. Methodology. The nature of the plasma interaction with the substrate material is determined by the ions energy and their flow density, other things being equal. The energy of the ions treating the substrate consists of their initial energy and the energy acquired in the Debye layer adjacent to the substrate when a negative potential is applied to it. The value of the potential at which the processes of condensation or sputtering are balanced is determined mainly by the nature of the vaporized material. When the value of the substrate potential increases, the deposited particles and its material are sputtered. At the same time, atoms on the substrate that are weakly connected to it, various impurities are removed, substrate temperature increases, especially in its surface layers. Results. The work investigates the influence of various metals and gases used to clean the surface of substrates made of cubic boron nitride PcBN and steels on the surface morphology. It was established that the use of gases (argon, nitrogen) for cleaning the surface of dielectric materials, in particular PcBN, showed the best results, which subsequently leads to an increase in the adhesion of the vacuum arc coating to the substrate. Practical value. The obtained results of investigation are of great practical importance. They can be used for the increasing of tool life and productivity of mechanical engineering.

Studying the new modes of deposition of plasma coatings

Problem. This paper considers using ion-plasma spraying of mold surfaces. This makes it possible to replace scarce and expensive tungsten-containing steels with other materials. Purpose. The purpose is to study the possibility of using the KIB method to increase the stability of die-casting molds, to establish the possibility of replacing scarce, expensive tungsten-containing steels with other materials. Materials and methods. 4Х5МФС and 5ХНМ steel grades were chosen as materials for copper alloy die-casting molds in this work. The choice of these steel grades is due to the fact that these steels do not contain tungsten due to its sharply increased scarcity and limited molybdenum content, and they also meet the requirements for the substrate material on which the titanium nitride coating is applied. Coatings were applied to samples for laboratory tests and die-casting mold parts by the condensation method with ion bombardment. Titanium nitride is applied at different partial nitrogen pressures – from 3×10-3 to 1 Pa to determine the required nitrogen pressure, which ensures that the working surfaces of mold parts receive coatings with the best performance characteristics. The coatings obtained at different nitrogen pressures differ in the amount and size of the droplet phase. Results of experiments. The largest amount of the droplet phase containing α-Ti is observed in coatings obtained at nitrogen pressures of 3×10-3 Pa, 3×10-2 Pa. An increase in nitrogen pressure (4×10-1 Pa, 1 Pa) significantly reduces the level of microdistortions of the crystal lattice in the coating, and its plasticity increases. In this regard, the coating's brittleness is reduced at a sufficiently high hardness. Results. The titanium nitride coating obtained at a nitrogen pressure of 1 Pa is the most effective in protecting the working surfaces of mold parts from destruction. Laboratory tests have shown that the titanium nitride coating applied under optimal process parameters increases the corrosion resistance of mold parts to which it is applied by 3 times and the scale resistance by 2-4 times.

The reinforcement strategy of electrophoretic deposition coating assisted by PVP for grain boundary diffusion of Nd-Fe-B magnet

In this study, we aimed to enhance the quality of electrophoretic deposition (EPD) coatings for Nd-Fe-B grain boundary diffusion (GBD) by addressing issues related to the adhesion and densification of coating. We introduced a novel approach by incorporating polyvinyl pyrrolidone (PVP) into an alcohol suspension containing TbH3 nano-powders. The addition of PVP resulted in the formation of a dense coating with superior adhesion and a smooth surface. To evaluate the effectiveness of the EPD coating with PVP, we compared the EPD rate of the TbH3 nano-powders alcohol suspension with and without PVP. The EPD rate of the suspension with PVP exhibited a significant 30-fold increase compared to the suspension without PVP, indicating a substantial improvement in the electrophoretic efficiency. Based on our experimental findings, we recommend depositing the EPD coating at a voltage of 120 V and adjusting the deposition time accordingly to achieve a desired coating weight percentage of 1.0 wt% with a thickness of approximately 30 μm. Following the GBD process, the coercivity of the magnet with PVP increased from 1131 kA/m to 1896 kA/m, which improved the high-temperature stability of the magnet. Overall, our research offers a promising approach to overcome the limitations associated with EPD coatings for GBD applications, providing a potential solution for enhancing the performance and industrial viability of these coatings.

Cellulose nanocrystals polyelectrolyte complexes as flame retardant treatment for cotton fabrics

In this work, polyelectrolyte complexes (PECs) are employed as an efficient way for the deposition of functional flame retardant coatings based on cellulose nanocrystals (CNCs). To this aim, CNCs have been combined with branched polyethyleneimine (BPEI) obtaining gel-like PECs to be deposited on cotton by an easy doctor-blading approach. The morphology of the coated fabrics was investigated by scanning electron microscopy. The thermal stability was evaluated by thermogravimetric analyses while the achieved flame retardant properties were assessed by horizontal flammability tests. The deposition of the CNCs/BPEI PECs produces a homogeneous coating capable of self-extinguishing the flame with only 8 % of weight added to the fabric. Post combustion residue investigations highlighted how these CNCs/BPEI PECs can produce a swelled charred barrier consisting of polyaromatic structures embedded within an amorphous carbon. The results reported in this paper open up to a practical and industrially viable strategy for the exploitation of CNCs in the field of flame retardant coatings.

Electrochemical method of deposition of an alumina coating on carbon fiber

Electrochemically produced oxide coatings have a wide range of potential applications. Despite this, works on the electrochemical deposition of aluminum oxide can be counted on the fingers of one hand, and carbon fiber has not previously been used as a substrate. This work aimed to test and study the mentioned method of depositing aluminum oxide coatings, examine the structure of the resulting coatings, and investigate the possibility of using carbon fiber as a substrate. In this work, we proposed a new method for electrochemical deposition of aluminum oxide coatings from an aqueous electrolyte. The method permitted obtaining uniform and continuous coatings with a thickness of about 300 nm on flat glassy carbon substrates. The effect of current density, deposition time, and electrolyte composition on the thickness and uniformity of the coating was studied. The proposed method was successfully applied to the deposition of the coating on carbon fiber. In addition, the coatings had sufficient continuity, and their thickness reached 100 nm.

High power pulsed magnetron sputtering tailored low temperature CrAlN + MoWS coatings for dry tribological contacts

Gears are used in a variety of applications, for example, in automotive and aerospace industries. In these applications, gears are exposed to harsh conditions such as high Hertzian pressures. In many cases, lubricants are used to achieve a reduction in the coefficient of friction and, thus, in the wear of the components. Nevertheless, in some applications, the use of a lubricant is difficult, for example, in vacuum environments. One promising approach is the application of solid lubricants by using triboactive elements. The present study shows the potential of a process combining high power pulsed magnetron sputtering (HPPMS) and direct current magnetron sputtering (dcMS) for the deposition of CrAlN + MoWS coatings. In HPPMS/dcMS processes, especially, the share of HPPMS leads to higher ionization of the coating plasma and, therefore, to higher coating thicknesses on the teeth of gears. One major challenge in coating processes is the adjustment of the deposition temperature, since steels used for gear applications are temperature sensitive. Therefore, starting from an established coating process with a high coating temperature, the coating process was adjusted by reducing the number of used cathodes. By reducing the count of used dcMS cathodes, the share of HPPMS cathodes within the coating process was increased. Furthermore, segments of gears were coated in order to determine the coating thickness at different distances from the head of the gear tooth. A sufficient coating thickness distribution on the flank of the gear tooth is crucial for friction reduction and wear protection when used in gearboxes. The reduction of used cathodes led to a decrease in the coating temperature from a maximum coating temperature of Tmax = 281 °C to Tmax = 214 and 197 °C. It was shown by nanoindentation measurements that the effect of soft annealing was eliminated by reducing the coating temperature. At the same time, coatings deposited with increased HPPMS fraction led to a reduced coefficient of friction as well as lower wear volumes for pin-on-disk measurements in a dry tribological contact with an uncoated 100Cr6 counterpart. Moreover, these processes exhibited a good coatability of the gear tooth with a relatively high coating thickness even near the gear tooth root. The present study shows the potential of increasing the share of HPPMS during the deposition of coatings for dry-running applications. By increasing the HPPMS content, the tribological behavior as well as the coating thickness distribution on gears can be significantly improved.

Atomic Layer Deposition of Lithium Borate and Borophosphate Thin Films for Lithium-Ion Battery Applications

Lithium-ion batteries (LiBs) are widely used in portable electronic devices and electric vehicles because of their high energy density and long cycle life. However, their performance is limited by unwanted side reactions that occur at the electrolyte-electrode interface during charge/discharge cycles.Previous studies have indicated that the application of a conformal and ultra-thin protective coating on the electrode surface through atomic layer deposition (ALD) is a promising strategy to prevent these undesired side reactions [1]. Due to their high stability, metal phosphates are deemed a promising class of materials for protective coatings, and several studies have focused on ALD of metal phosphates [2], with lithium phosphate as a particularly relevant material. However, the low ionic conductivity, as evidenced by the reported value of 1.4 x 10-10 S cm-1 with an activation energy of 0.92 eV for crystalline Li3PO4 films deposited by ALD [3] may hinder the flow of lithium ions through the coating. It has been shown, albeit using other deposition techniques, that the inclusion of borate species can enhance the ionic conductivity of phosphate materials, including lithium phosphate [4]. However, lithium borates exhibit a more narrow electrochemical stability window. Here, we investigate the combination of lithium phosphate and lithium borate into a new, intermixed ALD coating, i.e. lithium borophosphate, aiming to increase the ionic conductivity of the protective coating while preserving as much as possible its electrochemical stability.To date, only one ALD process for lithium borate has been reported by Kazyak et al. [5], which resulted in films with significant carbon incorporation. In this work, we have developed an ALD process for depositing lithium borate with minimal contaminants (< 5 at.% as determined by XPS) using LiHMDS, H2O and TMB as precursors. Through-plane impedance spectroscopy measurements were used to determine the ionic conductivity. For a lithium borate ALD film with a thickness of 81 nm deposited at 250°C, an ionic conductivity of 1.60 ± 0.03 x 10-7 S cm-1 was obtained at 30 °C, with an activation energy of 0.58 ± 0.01 eV.By combining this lithium borate ALD process with the well-known lithium phosphate ALD process [6], the composition of the film could be precisely controlled, resulting in tailored electrochemical properties. Cyclic voltammetry was employed to evaluate the electrochemical stability of the lithium borophosphate mixtures. The coatings were deposited on top of an ion-blocking material and cycled to high voltages. Initial results indicate that the stability of the coating material decreases as the amount of lithium borate to lithium phosphate cycles increases.These promising preliminary results demonstrate that ALD is a valuable tool in developing high-performance battery technologies, enabling the deposition of new protective coatings with controllable electrochemical properties. Finding the optimal lithium borophosphate coating will require a trade-off between ionic conductivity and electrochemical stability and will ultimately depend on the intended application. References Jung, Y. S., J. Electrochem. Soc. 157, A75 (2009).Henderick, L., Appl. Phys. Rev. 9, 011310 (2022).Put, B., J. Electrochem. Soc. 166, A1239 (2019).Magistris, A., J. Power Sources 14, 87 (1985).Kazyak, E., J. Mater. Chem. A 6, 19425 (2018).Hämäläinen, J., J. Electrochem. Soc. 159, A259 (2012). Figure 1

Ruthenium Electrodeposition from Non-Aqueous Electrolytes Containing Divalent Ions

Ruthenium as a metal is characterized by interesting technological and aesthetic properties, which make it an ideal choice for many applications. Ruthenium is dark grey in appearance, it presents a reduced tendency to corrode, low contact resistance and high hardness. When applied in the form of thin films, it can be used in jewels production, protection of electrical contacts, deposition of barrier layers in microelectronics and manufacturing of interconnects in integrated circuits [1].Ruthenium layers can be advantageously deposited exploiting electrodeposition, typically from aqueous sulfamate based electrolytes containing the metal in the form of a complex known as μ-nitridobisaquatetrachlororuthenate [Ru2(μ-N)(H2O)2Cl8]3-. These baths are routinely used at the industrial level and provide good coatings at acceptable cathodic efficiencies. However, ruthenium tends to oxidize in aqueous environment and the resulting deposits can contain impurities or oxides. In addition, the electrodeposition of ruthenium in water-based electrolytes presents difficulties when thick and crack-free coatings are required.In an attempt to solve these limitations, the use of non-aqueous electrolytes for the deposition of ruthenium coatings has been proposed. The substitution of water with alternative solvents can potentially relieve the problem of ruthenium oxidation. Moreover, non-aqueous electrolytes are characterized by wide potential windows, which translate into a reduction in the entity of parasitic hydrogen evolution reactions. Consequently, the properties of the deposit obtained can be potentially improved. In the context of non-aqueous electrolytes, ruthenium has been deposited from water and air stable ionic liquids [2, 3] and from deep eutectic solvents [4].With respect to our previous paper on the deposition of ruthenium [4], where the metal was deposited from the (IV) oxidation state, the present work describes a diametrically different approach. Indeed, we investigate the electrodeposition of ruthenium layers from a non-aqueous electrolyte based on ethylene glycol and containing the metal in its divalent state. The (II) oxidation state is obtained by reducing trivalent RuCl3 with ascorbic acid. A complete physical and electrochemical characterization of the resulting electrolytes is performed, demonstrating the reduction of Ru(III) to Ru(II). The deposition of thin and thick layers is attempted and the resulting coatings are characterized to exclude the possible presence of oxides or other secondary phases. Finally, the possible application of ruthenium layers for electrical contacts protection is evaluated.[1] R. Bernasconi and L. Magagnin, J. Electrochem. Soc. 166(1), D3219-D3225 (2019)[2] O. Raz, G. Cohn, W. Freyland, O. Mann and Y. Ein-Eli, Electrochim. Acta 54, 6042 (2009)[3] O. Mann, W. Freyland, O. Raz and Y. Ein-Eli, Chem. Phys. Lett. 460, 178 (2008)[4] R. Bernasconi, A. Lucotti, L. Nobili and L. Magagnin, J. Electrochem. Soc. 165(13), D620-D627 (2018)

Oxidative Molecular Layer Deposition of Conductive PEDOT Coatings Onto Polymer Sponges to Form Compressible Porous Electrodes

The formation of compressible porous sponge electrodes is appealing to overcome liquid phase diffusion in electrochemical applications including energy storage, water desalination, and electrocatalysis. Previous work has employed wet chemical synthesis to deliver conductive materials into porous polymer sponge supports, but these approaches struggle to produce functional electrodes due to (1) poor electrical connectivity of the conductive network and (2) mechanical rigidity of the foam after coating. In this work we employ oxidative molecular layer deposition (oMLD) via sequential gas-phase exposures of 3,4 ethylenedioxythiophene (EDOT) and molybdenum pentachloride (MoCl5) oxidant to coat polyurethane sponges with electrically-conductive and redox-active poly(3,4 ethylenedioxythiophene) (PEDOT) coatings. We analyze the oMLD deposition on compressible polyurethane sponges and modify the reaction conditions to obtain mechanically compressible and electrically conductive sponges. We specifically identify the importance MoCl5 dose time to enhance the conductivity of the sponges and the importance of EDOT purge time to preserve the mechanical properties of the sponges. This approach produces an electrically conductive PEDOT network within the sponge support with minimal impact on the sponge’s mechanical properties, offering advantages over wet-chemical synthesis approaches. The compressible, conductive sponges we generate have the potential to be used as compressible electrodes for water desalination, energy storage, and electrocatalysis.

One-Step PRC Surface Pretreatment for Plating Onto Al Alloys

Faraday will describe our recent work on the development of a one-step electrochemical surface preparation process to prepare aluminum alloys for direct electrodeposition. Coating on aluminum commonly requires extensive surface pretreatment processes prior to deposition, owing to aluminum’s reactive nature and affinity for oxygen, leading to the formation of an oxide film that negatively affects coating adhesion to the substrate. Therefore, preparing the surface is critical to remove any oils or dirt attached to the surface and to remove the native oxide film to increase coating adhesion. Conventionally these issues are addressed by a continuous sequence of twelve (12) pretreatment process steps to prepare the surface for deposition. Such an extensive number of processing steps requires significant capital investment for a new vendor, increases the probability of errors during the process, is time consuming (lower industrial throughput that ties up equipment), and requires large volumes of hazardous chemicals (Hydrofluoric Acid) that are environmentally unfavorable and introduce cost and safety concerns. Therefore, alternative techniques that do not require such extensive pretreatment processing with similar or better performance to conventional methods are desired.Faraday has recently developed a simple environmentally benign pretreatment process utilizing our pulse reverse electrofinishing approach that can dramatically reduce the number of procedures and complexities required to prepare the surface for the direct deposition onto Al alloys. A specific application of interest that requires low-cost, simple fabrication technology for the deposition of wear, erosion, corrosion fatigue resistant coatings onto Al is Neutrino Focusing Horns. Neutrino Focusing Horns, required for research on particle accelerators and storage rings, are commonly made of aluminum. These horns must withstand repetitive thermal and magnetic loadings over millions of pulses in a radiation and corrosive environment and the thickness of the inner conductor is minimized to reduce absorption and scattering of secondary particles in the conductor material. Therefore, protection of the focusing horns from erosion, corrosion and fatigue is of critical importance to assure long time reliability. The most successful coating thus far has been an electroless nickel coating with conventional 12 step pretreatment method. The application of this coating, however, is challenging due to the large size of the horn (4 m x 1 m x 1 m), and industrialization is challenging due to the low part volumes, high capitalization and large number of process steps.This presentation will focus pulse/pulse reverse surface preparation processes being developed by Faraday Technology. It will explore surface pretreatment procedures to simultaneously prepare various Al surfaces such as Al 6061, Al 4043, Al 1100, and Al 5086 and subsequent direct deposition of ZnNi, NiP, or Ni coatings. These coating have since been characterized and compared to baseline electroless NiP coatings for their functional properties. The results of these characterization studies will be discussed in detail.

Corrosion-Resistant and Electrically Conductive Oxide Coatings for Metal Bipolar Plates for PEM Electrolyzers

The PEM electrolyzers are considered a promising alternative to alkaline water electrolyzers, as the advantages of PEM technology are high efficiency, high power density, a wide range of power inputs, low operating temperatures, relatively quick start-up, and easy scale-up. The ability of PEM electrolyzers to function dynamically makes them particularly appealing in energy capture and storage systems where electrical energy is derived from renewable sources such as solar and wind power. The bipolar plates (BPPs) are essential components of the PEM electrolyzer stacks and account for the main fraction of the total weight and cost. The BPPs must be electrically conductive, highly corrosion-resistant, and maintain a low interface contact electrical resistance (ICR). The root causes of the BPPs corrosion issues are non-conductive oxides formation increasing electrical resistance, and metal ions out-diffusion poisoning the catalyst and electrolyte membrane. The US Department of Energy has set targets for bipolar plates in fuel cells, including corrosion current densities < 1 µA/cm2 and ICR < 10 mΩ·cm2. Even though these targets do not apply to BPPs in PEM electrolyzers, they provide an indication of acceptable values. The problems outlined above are being overcome or minimized by applying corrosion-resistant and simultaneously electrically conductive coatings.This work, therefore, investigates various corrosion-resistant and electrically conductive oxide coatings prepared by reactive high-power impulse magnetron sputtering (HiPIMS) on SS316L substrates. Reactive HiPIMS is an advanced and progressive magnetron sputter deposition technique suitable for preparing high-quality oxide coatings. The main advantage of HiPIMS is a high degree of ionization of sputtered particles in the discharge plasma and the associated high ion-to-atom ratio in particle flux toward the substrate. This allows one to achieve coating densification and crystallinity at low substrate temperature and without applying a substrate bias voltage. In our case, the native oxide on the SS316L substrate surface was removed by employing plasma etching prior to the coating deposition utilizing HiPIMS-generated ions accelerated towards the substrate by an applied bias voltage. The oxide coatings were deposited using an unbalanced magnetron with a directly water-cooled planar target with a diameter of 100 mm in argon-oxygen gas mixtures at the argon pressure of 1 Pa in an ultra-high vacuum chamber. The oxygen partial pressure was controlled by a PID regulator at a given power density in a pulse. This allowed the deposition of the coatings with different stoichiometries and, thus, different electrical conductivity and corrosion resistance.The electrical resistivity of oxide coatings was measured by a four-point probe system on a non-conductive glass substrate. The compaction pressure dependence of ICR between the test plate and a gas diffusion layer (GDL) was measured in a range from 0.3 to 2.0 MPa on a custom-designed device using gold-coated cylindrical copper electrodes. All electrochemical measurements were performed in an H2SO4 electrolyte solution with an acidity of pH 5.5, fluorine ions concentration of 5 ppm, and a temperature of 60 ℃ to simulate the PEM electrolyzer environment. Accelerated corrosion tests were carried out in extreme anodic conditions of the PEM electrolyzer via potentiostatic polarization at a potential of 2 V vs SHE. Open circuit potential, corrosion current, Tafel slopes, and polarization resistance were determined from potentiodynamic polarization curves measured from 0 to 2 V vs SHE recorded at a scan rate of 1 mV/s, this range should cover most of the potentials experienced inside a PEM electrolyzer. Potentiodynamic polarization and ICR versus compaction pressure were measured before and after the accelerated corrosion test.

Deposition of Multi-Ceramic Aluminium-Matrix Composite Coating by Direct Laser Deposition

Using of metal matrix composite coating is a promising approach for improving the surface properties of a component against the mechanical and environmental attacks especially wear and corrosion. Laser cladding (LC), also known as direct energy deposition (DED), is an additive manufacturing (AM) technique, able to perform coating, repair worn parts, manufacturing and prototyping. In this work, pure Al and a mixture of multi-ceramic Al-15SiC-15Al2O3 coatings were successfully deposited on Al-based substrate. The quality of the deposited clads was evaluated according to macro-graphic, microstructure, and microhardness characteristics. The microscopic inspection of the multi-ceramic coatings showed a slight dilution of SiC particles. Also, XRD investigation revealed a formation of Al4C3 carbide. Besides SiC and Al2O3 hard phases, this yielded an increase in matrix microhardness about 180% (from 75 to 212 Hv0.05) as compared to pure Al clads, indicating a great improvement in the mechanical properties of the composite cladded coating.

Electrochemical deposition and characterisation of NiTi alloy coatings for better corrosion protection

ABSTRACT The present study reports the electrochemical deposition and characterisation of Nickel-Titanium (NiTi) alloy coatings on mild steel (MS) from citrate bath having nickel sulphate and titanium oxysulphate as salts, tri-sodium citrate as complexing agent and glycerol as the brightener. Bath composition and operating variables were optimised by the conventional Hull cell method for bright and uniform coating. NiTi alloy coatings were developed at varied current densities (1.0 A/dm2 to 4.0 A/dm2), keeping pH = 4.0. The corrosion behaviours of NiTi alloy coatings were evaluated by electrochemical AC and DC methods in a 3.5 per cent sodium chloride solution. X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray Spectroscopy (EDS) techniques were used to study the phase structure, surface morphology and chemical composition of the coatings, respectively. The observed facts stand to the reason that the bath follows induced type co-deposition in the range of current density studied. Corrosion studies validated that NiTi alloy coating deposited at 4.0 A/dm2 is the most corrosion-resistant among all other current densities. This highest corrosion stability of NiTi alloy, corresponding to 4.0 A/dm2 is attributed to high wt.% of Ti (i.e. 3.5%). The decrease in corrosion rate towards high current density was analysed and discussed.

Towards a Better Understanding of the Back-Side Illumination Mode on Photocatalytic Metal–Organic Chemical Vapour Deposition Coatings Used for Treating Wastewater Polluted by Pesticides

Pesticides are emerging contaminants that pose various risks to human health and aquatic ecosystems. In this work, diuron was considered as a contaminant model to investigate the influence of the back-side illumination mode (BSI) on the photocatalytic activity of TiO2 coatings grown on Pyrex plates by metal–organic chemical vapour deposition (MOCVD). A photoreactor working in recirculation mode was irradiated at 365 nm with ultraviolet A (UVA) light-emitting diodes in BSI. The degradation of diuron and its transformation products was analysed by high-performance liquid chromatography, ion chromatography, and total organic carbon analysis. The coatings were characterised by X-ray diffraction analysis and scanning electron microscopy. Five coatings containing 3, 7, 10, 12 and 27 mg of TiO2 exhibited different morphology, crystallinity, thickness and photocatalytic activities. The morphology and crystallinity of the coatings had no significant influence on their photocatalytic activity, unlike their mass and thickness. TiO2 contents less than 10 mg limit the photocatalytic activity, whereas those greater than 15 mg are inefficient in the BSI because of their thickness. The maximum efficiency was achieved for coatings of thickness 1.8 and 2 µm with TiO2 contents of 10 and 12 mg, revealing that the photocatalyst thickness controls the photocatalytic efficiency in the BSI.

Effect of laser power on microstructure and properties of laser assisted cold sprayed copper coatings on steel

Laser assisted cold spraying (LACS) is a promising technology for preparing high performance copper-steel composite materials for grounding electrode applications. Laser power is a critical LACS parameter, however, in literature there is a lack of studies on the influence of laser power on coatings. In this study, the effect of laser power on microstructure and properties of LACS copper coatings on steel is investigated. The results show that with the increase of laser power, the copper coating generally shows reduced porosity and microhardness, as well as increased bonding strength. However, the grains are first refined and then coarsened, while the electrical conductivity and corrosion resistance both increased and then decreased. This is because when the laser power exceeds 4 kW, the grain is coarsened and the amount of large angular grain boundaries (HAGBs) increases because excessive temperature increases the recrystallization driving force, ultimately leading to decrease in coating electrical conductivity and corrosion resistance. 4.0 kW, 5 MPa, 800 °C is considered as optimal LACS parameters for preparation of pure copper coatings on Q235 steel. The coating has a porosity of <0.04 %, grain size of 0.634 μm, microhardness of 99.4HV0.1, bonding strength exceeds 62 MPa, electrical conductivity of 99 % IACS, and corrosion current density of 6.092 × 10−8 A/cm2. In addition, mechanisms of LACS particle deposition and corrosion of copper coatings in simulated soil solution were discussed. With the increase of laser power, more heat absorbed by the powder and the substrate promotes thermal softening and plastic deformation, resulting in stronger mechanical bonding. The corrosion mechanism gradually changes from pitting corrosion to uniform corrosion due to the reduced porosity and tighter grain boundaries, and finally to intergranular corrosion due to grain coarsening and high HAGBs content. Overall, this study provides guidance and reference for the practical application of LACS.

On the deposition of cold-sprayed hydroxyapatite coatings

Cold spraying is a well-established coating fabrication method for metals onto metallic substrates. Over the past decade, there has been a growing interest in its application as a deposition technique for hydroxyapatite (HAp) coatings due to its lower processing temperatures compared to conventional coating manufacturing techniques. HAp coatings are ceramic coatings employed in biomedicine for their biocompatibility and osteoconductive properties. The deposition of ceramic coatings using cold spraying remains a challenge due to the brittle nature of these materials when subjected to high-velocity solid-state impacts. In the present study, HAp deposits were produced via low-pressure cold spraying onto 316 stainless steel under various processing conditions to induce different energy states upon impact and elicit distinct responses in the deposited material. The morphology of the deposited HAp particles was examined after single-track experiments to comprehend the characteristics of the particles adhering to the substrate surface after each experiment. The study was supplemented with impact energy calculations, which allowed the establishment of processing windows to form HAp deposits and coatings. A cold-sprayed HAp coating was successfully obtained within the suggested range of experimental conditions based on energy calculations.

High Rate, Dendrite Free Lithium Metal Batteries of Extended Cyclability via a Scalable Separator Modification Approach.

Owing to their great promise of high energy density, the development of safer lithium metal batteries (LMBs) has become the necessity of the hour. Herein, a scalable method based on conventional Celgard membrane (CM) separator modification is adopted to develop high-rate (10 mA cm‒2) dendrite-free LMBs of extended cyclability (>1000 hours, >1500 cycles with 3 mA cm‒2, the bare fails within 50 cycles) with low over potential losses. The CM modification method entails the deposition of thin coatings of (≈6.6 µm) graphitic fluorocarbon (FG) via a large area electrophoretic deposition, where it helps for the formation of a stable LiF and carbon rich solid electrolyte interface (SEI) aiding a uniform lithium deposition even in higher fluxes. The FG@CM delivers a high transport number for Li ion (0.74) in comparison to the bare CM (0.31), indicating a facile Li ion transport through the membrane. A mechanistic insight into the role of artificial SEI formation with such membrane modification is provided here with a series of electrochemical as well as spectroscopic in situ/ex situ and postmortem analyses. The simplicity and scalability of the technique make this approach unique among other reported ones towards the advancement of safer LMBs of high energy and power density.

Формирование и исследование свойств покрытий из металлического стекла FeWCrMoBC на стали 35

Introduction. To obtain metallic glass coatings it is necessary to achieve high cooling rates of melt. FeWCrMoBC composition has high melt viscosity and sufficient glass-forming ability to fix of the amorphous state at cooling rates implemented by electric discharge alloying with the use of a crystalline electrode. The purpose of the work is one-stage deposition of amorphous coating by electric discharge alloying, using crystalline anode FeWCrMoBC, prepared by casting and studying the properties of modified surface of carbon steel: wettability, high-temperature resistance, tribological properties. Methods and Results. The structure of anode and coatings was investigated by X-ray diffraction analysis in CuKα radiation on a DRON-7 diffractometer. In contrast to the X-ray patterns of the anode material, sharp Bregg reflexes were not observed on the X-ray patterns of the coatings, but a wide halo was present in the range of angles 2Ѳ = 40–50°, which indicates its amorphous structure. The cyclic high-temperature resistance test was carried out at 700 °C for 100 hours. The wear rate and coefficient of friction of the specimens were studied under dry sliding friction at a speed of 0.47 m/s at a load of 25 N with the use of a counterbody made of high-speed steel M45. The influence of the discharge pulse duty cycle on the character of mass transfer (anode erosion, cathode weight gain, mass transfer coefficient) during coating formation was investigated. With a decrease in the duty cycle of the discharge pulses up to 9 times, the erosion of the anode increased up to 5 times, and the cathode mass gain increased up to 2.2 times. The maximum mass-transfer coefficient was achieved at the highest duty cycle. An increase in a number of surface properties of carbon steel after coating was observed: the hardness of the surface of the specimens increased by 2.3–2.6 times; the average thickness of the coatings was in the range of 56–80.6 µm; the wetting angle was in the range of 108.4–121.3°; the coefficient of friction decreased by 1.2–1.4 times; the wear resistance increased by 2–3.3 times; oxidizability in air decreased by 14–18 times. Scope and Conclusions. The achieved higher properties (hardness, wear resistance, high-temperature resistance, and hydrophobicity) of the executive surfaces of parts made of carbon steel after deposition of the proposed coatings can be used in various branches of engineering production. The results of the work confirmed the possibility of deposition of metallic glass coatings by electric discharge alloying with the use of cast anode material FeWCrMoBC on carbon steel.