Showing papers in "Surface Engineering in 2023"

Nanolubrication and tribological behaviour of the rolling process – a review

Abstract: ABSTRACT The purpose of the present article is to dispense an extensive review of research works performed to observe the impacts of nanoparticles tribologically and rationalise the use of nanoparticles in metal rolling lubrication. The results of past experimental research were analysed based on tribological behaviour, lubricant characteristics, and rolling quality. Improvements in tribological behaviour, rolled surface characteristics and mechanical strength were illustrated in the present work. A specific concentration of nanoparticles in the base lubricant was discovered which provided beneficial outcomes. The oxide scale formed as an inevitable byproduct is suppressed by the nano-application. The nanoparticles served better in the rolling process in terms of temperature control due to the enhanced thermal conductivity of the base lubricant. The article advocates for the adoption of nano-lubrication in replacement of traditional lubricating fluids in the rolling process. The article lastly presents future challenges and the potential of nanolubricants in engineering applications.

Long-term oxidation of MoSi2-modified HfB2–SiC–Si/SiC–Si coating at 1700°C

Abstract: ABSTRACT Slurry impregnation and gaseous Si infiltration were effectively used to produce compact MoSi2-doped Si–HfB2–SiC/Si–SiC (HMSS/SS) coatings with a thickness of 250 μm to protect carbon fibre reinforced carbon (Cf/C) composites from oxygen corrosion at 1700°C. The HMSS/SS coating obtained with a mosaic structure makes it possible to protect Cf/C composites at 1700°C for 276 h and the mass reduction is only 0.99%. The pinning effect of the embedded hafnia, the generated MoB together with the Hf, Mo co-doped Si-based glass layer, which successfully prevented the migration of oxygen, was attributed to the superior oxidation protection ability of the HMSS/SS coatings. This work provides a practical method for successfully extending the service life of Cf/C composites in the aerospace industry.

Microstructure and surface quality of SLM printed miniature helical gear in LSPwC

Abstract: ABSTRACT The present work describes the influence of underwater laser shock peening without coating (LSPwC) on selective laser melting manufactured meso-size (outside diameter ≤ 10 mm) helical gears. Five experiments were conducted using energies in the 200 mJ up to 1 J, while the spot size and overlap were kept constant as 1 mm and 90 %, respectively. Responses were measured and compared in terms of surface residual stresses, surface roughness, and microstructure of LSPwC-treated samples. Results show the development of significant compressive residual stresses in the root of the LSPwC processed helical gear, where it changes the state from tensile +45 MPa to compressive −421 MPa. Surface roughness has shown improvement, while volumetric material peak confirms the reduction by over 50%. Microstructure study was performed at the surface and by cross-section using scanning electron microscopy and electron backscatter diffraction analysis. The grain refinement and change in misorientation were observed, confirming plastic deformation.

Functional surfaces through texture management

Abstract: Surfaces define the outer boundaries of an object and interact with the surrounding medium in a multitude of ways. Surface texture, defined as “the local deviation of a surface from a perfectly flat plane “[1], is a crucial determinant of the functionalities of various materials, be they natural or man-made. In nature, surface texture has evolved to meet the diverse survival needs of living organisms. For instance, Darkling beetles Figure 1(a) and some types of cacti Figure 1(b) that inhabit desert environments possess specialised bumps, grooves, or 3D hierarchical structures on their body surfaces, which condense water from the air [2,3]. The surface texture of the lotus leaf Figure 1(c) is the most cited example of hydrophobic surfaces, bordering on being a cliché. Manmade surface textures can be perceived as nominal or actual. The nominal surface refers to the intended contour of the surface, while the actual surface is determined by the manufacturing processes used to create it [5]. Surface texture is typically categorised into roughness, waviness, lay, and flaws Figure 2. Roughness is determined by the characteristics of the materials and processes used to form the surface and manifests as small, finely-spaced deviations from the nominal surface. Waviness, on the other hand, consists of much larger deviations caused by factors such as work deflexion, vibration, and heat treatment. Roughness is typically superimposed on waviness. The lay of the surface texture refers to the predominant direction or pattern of the surface, while flaws are irregularities that occur occasionally on the surface, such as cracks, scratches, and inclusions. Although flaws are related to surface texture, they also affect surface integrity. The texture of a surface can contribute to aesthetics, safety, assembly, and functionality. For example, the shininess or dullness of a surface can impact its perceived aesthetic value, while the surface’s mechanical properties, absorption, friction and wear, corrosion and wear behaviour, adhesion, and electrical and thermal conductivity, can affect its overall functionality. Smooth surfaces are better suited for electrical contacts, while rough surfaces are better suited for water repellency and friction like in brakes. The texture is the single driving cause for the presence or absence of friction between mating surfaces. As early as the 18th century, Bernard Forest de Bélidor recognised that friction arises from the numerous hemispherical peaks and valleys on the mating surfaces, a concept furthered by Coulomb in his exposition of lubrication [8]. There are various categories of texturing methods, including addition, removal, displacement of material, and self-forming methods [9]. The most common industrial texturing processes such as shot blasting, milling, grinding, etching, lithography, laser methods, and manual polishing fall under the removal category. Replica methods such as master printing and microcontact printing, and 3D additive manufacturing are addition-based methods. Each of these techniques has its unique advantages and disadvantages, and the selection of the appropriate method depends on the type of surface, the desired texture, and the required accuracy. For example, shot blasting is ideal for creating a rough texture on a metal surface, while etching is useful for producing precise patterns on glass. All these methods are industrially available and the economies of scale have been achieved for specific functionalities and applications Additive manufacturing methods have enabled the production of complex and multi-scale materials with intricate submicron and nano-dimensional architectures, mimicking nature more closely than ever before [10]. Two-photon lithography (TPL), for example, can produce three-dimensional (3D) structures with submicrometer resolution of any complexity [10]. By controlling the shape, size, and distribution of surface features at the submicron and nanoscale Figure 3, it is now possible to create surfaces with unprecedented capabilities, such as tailorable superhydrophobicity [11], enhanced tribological performance, and increased biocompatibility. Femtosecond laser microfabrication has recently allowed for the nanotexturing of solid surfaces to exhibit superhydrophilicity in air and superoleophobicity underwater, mimicking fish scales Figure 4. Some of the applications of biomimetic submicron topology engineering have gone beyond academic interest and offer real-world solutions. One such example is the development of fog harvesting

A mechanically durable induction heating coating with desirable anti-/de-icing performance

Abstract: The anti-/de-icing technology based on induction heating offers significant advantages regarding fast heating, high efficiency, safety and environmental protection. However, the reported methods require the modification of base materials, which lacks universal applicability. Here, a universal and facile anti-/de-icing method is proposed based on induction heating. The durable induction heating coating was prepared by one-step spin coating with micron-sized nickel powder, epoxy resin and silicone resin. The induction heating ability of this coating was investigated by adjusting the proportion of composition, particle size and thickness. An optimal induction heating ability was achieved with the mass ratio of nickel powder and resin, particle size of nickel powder and coating thickness being 1.5, 7 μm and 1070 μm, respectively. We further show this coating can be applied for anti-/de-icing, demonstrated by its excellent de-/anti-icing performances. Finally, the mechanical durability of the coating was verified by the tape peel and sandpaper friction.

Effect of WC/C coated rolling element to improve bearing life

Abstract: ABSTRACT The research is aimed to understand the effect of WC/C coating on the bearing rolling elements to improve fatigue life in surface distress conditions. The 1–1.5 microns optimized coating thickness was deposited on the steel substrate using the PVD process. The coating’s physical and chemical properties were analysed by X-ray diffraction, scanning electron microscope, contact profilometer, nanoindentation hardness, and micro scratch indenter. The wear properties were compared on a ball-on-disc tribometer with and without a coated specimen. The bearing tests were performed in contaminated and clean lubrication conditions to prove the coating’s effect on bearing life in surface distress conditions. Results show that coated roller bearings perform at least two times that of the standard bearing. The overall benefit of less friction and wear resistance was due to the polishing action and coating transfer mechanism of multi-layer coating which increases oil film thickness between contacts and hence improve bearing life.

Substrates and preparation layers under the wall paintings of the St George’s Cathedral (1119 CE) at Veliki Novgorod

Abstract: ABSTRACT The Cathedral of St. George is located in the Yuriev Monastery, in Novgorod, one of the capitals of ancient Rus (The Great Novgorod). The wall paintings were completed around 1120 CE. The Cathedral or its parts were renovated in different periods. The fragments of the twelfth-century frescoes were deposited under the new floor and in the area around the Cathedral. Archaeological excavations of the Institute of Archaeology of the Russian Academy of Sciences in Moscow brought to light a large number of fragments of frescoes. The Laboratory for Architectural Archaeology and Multidisciplinary Methods in Architectural Research of the Institute began to study the fragments in 2021 and presents here the first results of the research on substrate and preparation layers of the paintings. Our aim was tdistinguishing the different phases of the wall paintings. The plasters used in the twelfth century are different from the later ones and contain different aggregates.

Superhydrophobic DTMS/rGO-nanocomposites modified polyurethane sponge for efficient oil–water separation

Abstract: ABSTRACT Dodecyltrimethoxysilane (DTMS)-modified reduced graphene oxide (rGO) nanocomposites were incorporated into polyurethane (PU) sponges by a combination of dip-coating and thermal curing reduction reaction to obtain a novel superhydrophobic DTMS-rGO-PU sponge for effective oil/water separation. The reaction conditions, such as the dip-coating solution concentration, the thermal curing reduction temperature, and the reaction time were demonstrated to be key factors in forming hierarchical DTMS-rGO nanocomposites, which significantly affected the surface wettability of the PU sponge. The resulting DTMS-rGO-PU sponge with a static water contact angle (WCA) of 152.2° displayed superior superhydrophobicity, and achieved an oil–water separation efficiency of 99.89% for various oil/water mixtures. This superhydrophobic sponge also showed minimal deterioration in its high oil adsorption capacity after 100 recycled adsorption operations. Furthermore, the as-prepared DTMS-rGO-PU sponge was proven to be physically and chemically stable and durable in harsh environmental conditions, suggesting its potential for industrial applications in oil spillage management.

Wear and corrosion behaviour of the cryogenically treated tungsten carbide coatings

Abstract: ABSTRACT The WC–12Co coatings were deposited on SS 410 substrates using a high-velocity oxygen fuel (HVOF) process and the coatings were heat-treated at 750°C for 1 h in argon environment. Further, the coatings were subjected to cryogenic treatment for 1, 2, 8 and 24 h, and its influence on the reciprocating sliding wear and corrosion characteristics was studied. The structural changes in the coatings after post-treatment were assessed by X-ray diffraction analysis and Raman spectroscopy. Microhardness was improved for cryogenically treated coatings due to the α-Co transformation into ϵ-Co. Cryogenic treatment duration was not having a significant effect on the microhardness values. However, the specific wear rate was influenced by the cryogenic treatment duration. Also, corrosion resistance was increased with the increased cryogenic treatment duration. The protective layers consisting of WO3 and Co3O4 phases formed during the cryogenic treatment are attributed to the improved corrosion resistance of the coatings.

Influences of Sc(NO3)3 on characteristics of micro-arc oxidation coatings

Abstract: ABSTRACT Micro-arc oxidation (MAO) coatings were fabricated on 2195 aluminium-lithium alloy substrate, using a silicate and phosphate electrolyte with variable scandium nitrate (Sc(NO3)3) concentrations. The properties of the coatings were analysed by scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electrochemical workstation. The comprehensive analysis demonstrates that adding proper amount of Sc(NO3)3 increased the oxidation voltage, which transformed the worm shape discharge micropores into round-hole shape, and the MAO coatings presented a double-layer structure. The primary phase composition of the coatings was γ-Al2O3, α-Al2O3, Sc2O3 and Al3Sc. The optimum concentration of Sc(NO3)3 was 0.6 g L−1. The hardness reached a maximum value of (1284 ± 43.5) HV, which was about 2.5 times higher than that without adding. The self-corrosion current density reduced from 138.00 × 10− 7 A cm−2 (substrate) to 3.65 × 10− 7 A cm−2, which was approximately two orders of magnitude lower, indicating that the corrosion resistance was improved.

Investigation of the tribochemical reaction mechanism in dry-type CMP of 6H-SiC substrate

Abstract: ABSTRACT In this paper, the tribochemical reaction mechanism between solid powder and 6H-SiC substrate was investigated. White light interferometer was used to detect surface roughness, FESEM was used to observe surface characteristics, EDS was used to detect surface elements and XRD was used to detect surface components. The tribochemical reaction mechanism of the reduced iron powder, anhydrous sodium carbonate and deionized water with 6H-SiC was analysed by the detection results. It is found that the reduced iron powder, anhydrous sodium carbonate and deionized water react with the 6H-SiC surface to form a soft interfacial transition layer which can be removed. The removal rate of the reduced iron powder is the highest at 191 nm h–1. The surface quality decreases after polishing with the anhydrous sodium carbonate. The results of this study provide a new idea for the field of ultra-precision machining.

Flame retardant and anti-dripping polyethylene terephthalate fabric based on bio-based phytic acid/gelatine coating

Abstract: ABSTRACT The application of polyethylene terephthalate (PET) is restricted due to its high flammability and dripping phenomenon. This paper used bio-based phytic acid (PA) and gelatine (G) for flame retardant and anti-dripping treatment of PET fabric. The coated PET fabric achieved a limiting oxygen index (LOI) value greater than 29.5% and no dripping phenomenon revealing that its flame retardancy and anti-dripping properties were obviously improved. The LOI value of PA/G coated PET fabric after washing was over 26% showing good washing durability. The PA/G coating could change the starting decomposition stability and the degradation process of PET fabric and promote to form the stable char. PA/G coating formed an intumescent flame retardant (IFR) system on PET fabric to act through the IFR mechanism. This research is expected to result in a novel eco-friendly coating for flame retardant and anti-dripping thermoplastic polyester fabric.

Laser shock peening: a promising tool for enhancing the aeroengine materials’ surface properties

Abstract: ABSTRACT Laser shock peening (LSP) is a unique and efficient surface modification technique that surface engineers have commonly adopted to tailor metallic materials’ surface and subsurface properties. The primary goal of this review paper is to highlight LSP as a surface modification technique for materials used in aeroengine, as this further ameliorates the commercialization of LSP in aeroengine sectors. The recent research articles focused on the application of LSP to improve the surface characteristics (i.e. surface residual stresses, hardness) and to resist the corresponding service challenges (i.e. fatigue, wear) of the aeroengine metallic material have been reviewed. In addition, a brief explanation of LSP and its controlling parameters is included. From the aeroengines perspective, challenges and future aspects for improving LSP application and commercialization are summarised based on the authors’ experience and published literature.

Wear behaviour of different nano particles coating on Al6061 substrate

Abstract: ABSTRACT The tribological behaviour of Ni-based composite coatings on Al6061 substrate with secondary phase hard oxide particles like ZrO2, TiO2, and Al2O3 at different elevated temperature conditions was compared. The composite coatings with different reinforcement of nano particles were characterized by scanning electron microscopy and X-ray diffraction technique. The higher microhardness value is reported for the Ni coating with TiO2 particles and Al2O3 particles. At higher temperature limits of 120°C and 140°C Ni–ZrO2 coatings have found better specific wear rate. The Ni–Al2O3–TiO2–ZrO2 composite coating fails to achieve better properties due to higher agglomeration of the particles and dendrite growth. The Ni–Al2O3 coating showed steady wear behaviour at different temperature limits. The coefficient of friction values is found nearly similar for all the type coatings at 40°C and 120°C.

Study of the electroplating process parameters on the electrical resistance of an aluminium alloy with a Cu-graphene-based coating

Abstract: ABSTRACT This study investigates the effects of the electroplating process parameters, such as temperature, graphene concentration in the bath and current density, on the electrical properties of a copper-coated aluminium alloy (AA6082). Based on previous experiences, a full factorial plan was developed and tested through the Design of Experiments (DOE) methodology to find a relation between parameters and properties. After validating the setup and the significance of the three input process parameters, a statistical model for copper electrodeposition is presented; the latter takes into account the physical interaction of the graphene nanoplatelets (GNP). From the results, the GNP amount is able to modify the electrical resistance of the copper coating; in detail, the resistance passes from 0.0319 to 0.02 mΩ, allowing a reduction of about 35% at the highest GNP content. Furthermore, an optimization following the new experimental model to decrease the electrical resistance of the graphene-based coating is presented. GRAPHICAL ABSTRACT

Production of a superhydrophobic frame-cone structure by laser etching and Ni electrodeposition

Abstract: ABSTRACT Metal components in microelectromechanical systems are prone to failure and corrosion due to droplet adhesion in wet environments. Several multi-level structures on the micro-nano scale may induce effective superhydrophobicity to prevent such adhesion. This study proposes a hybrid manufacturing process to generate ‘frame-cone’ textures on the surfaces of metals by combining ultra-fast laser etching and electrodeposition. Periodically distributed frame recesses and pits were coated with nano-submicron Ni coatings with conical shapes, and the pit depth and cone height were controlled by tuning the laser scanning time and current density, respectively. The surface adhesion force was reduced to 22.8 μN, and the static contact angle was maintained at 156.7° using the hybrid process, while the adhesion forces of laser etched samples with the same depth were 164.7 μN. The multi-level ‘frame-cone’ structure stored more air and reduced the contact areas between the bottoms of the pits and droplets. The hybrid process of ultra-fast laser etching and electrodeposition aided in improving the superhydrophobicity, with less damage to the substrate.

Sol-gel coatings for corrosion protection

Abstract: The above excerpt from an English Translation of Pliny the Elder’s Latin book on Natural History dated 77 CE may perhaps be the earliest written record of the use of a sol-gel type anticorrosion coating on metals. The war of man against corrosion has been relentless. We have devised various ways to protect various metals from corrosion – through judicious materials selection, application of various kinds of inorganic and organic coatings, using corrosion inhibitors, cathodic protection, and design elements that prevent corrosion. However, nature likes to revert back to its lowest thermodynamic form as an oxide from which we extract almost all materials for industrial use. Although modern scientific literature on corrosion protection coatings can be traced back to the era of pack cementation and electrodeposition in general, followed by aluminizing of iron in the twentieth century, the systematic study of sol-gel type coatings mitigating corrosion is relatively recent. Sol-gel is a surprisingly simple process that involves dipping the substrate with a sol to form a tacky, adherent gel film on curing, which then may or may not be subsequently calcined to get a microporous and mesoporous protective organic, inorganic or hybrid corrosion protective coatings. The advantages of sol-gel coatings, vis., benign conditions of deposition (e.g. relatively low temperatures) and the ability to produce coatings on complex shapes without the need for machining or melting (hence no expensive equipment) has led to a significant amount of work on sol-gel based protective coatings primarily for metals. The ease of application led to a burst of research since the turn of the century (Figure 1) has also been driven by the need for creating environmentally friendly materials and processes to replace the traditional chromium-based and/or solvent-based anti-corrosion coatings. Sol-gel-based coatings can be brought about through an inorganic or organic route. The former, which was probably the technique described by Pliny the Elder at the start of the Common Era, involves the gelation colloidal suspension of nanometric particles of inorganic materials (e.g. lead oxide, lead carbonate, and calcium sulphate in Pliny’s antipathia) to form a network in a continuous liquid phase. This is however rarer than the organic route in which a prepolymer is polymerized into a gel to form a protective network. The alkoxide-based process – the formation of an oxide (usually silicon oxide) network by progressive condensation of a metalloid alkoxide in a liquid medium is a classic example (Figure 2). In this alkoxide route, subsequent sintering the gel-coated substrate to high temperatures (440–1200°C) for short heating times, about 15 minutes, leads to the hardening of the coating to various degrees due to the formation of the oxides. Alkoxide-based sol-gel corrosion coatings have many benefits such as ease and flexibility of the fabrication process, the abundance of commercially available precursor reagents with tailored functional groups, and their low environmental impact. Additionally, there is excellent control over precursor stoichiometry and the ability to integrate diverse components that introduce complementary functions. Alkoxide-based sol-gel-generated SiO2, ZrO2, Al2O3, TiO2, and CeO2, coatings. have all been studied at various times because of their excellent chemical stability and provision of effective protection to the metal substrate. However, alkoxysilanes, such as tetra-oxy silicate (Si(OR)4) and organically modified silicates (Ormosils, R’nSi(OR)4−n) have been the most frequently studied precursors for sol-gel generated SiO2-based coatings [2]. The thickness and nature of these coatings can be modified by controlling the rheology of the sol, by using additives, or by modifying the reaction conditions including drying time and calcining temperature. Multi-component oxide coatings have been developed to overcome the limitation of single-component oxide layers, broaden their application areas and improve the comprehensive protective ability of steel substrates. Composite coatings containing SiO2 and ZrO2 or Al2O3 have been shown to act efficiently as corrosion protectors of 316L stainless steel substrates in aqueous NaCl and acid media at RT [3]. Hybrid silica-titania hybrid coatings containing cerium (III)

Antifouling activity of superhydrophobic PDMS/hydrophobic silica coating

Abstract: ABSTRACT This paper assessed the antifouling activities of a superhydrophobic surface with a contact angle of 161.6° and a sliding angle of 4.1° which can be employed on large scales. The preparation of PDMS/silica nanoparticles composite was first described for the production of superhydrophobic surfaces with different contents of silica nanoparticles. Then, the surface roughness of the produced samples was investigated. Subsequently, the surface reaction against the algae was evaluated at different immersion times. The samples coated with PDMS-to-Silica ratio of 100% exhibited higher stability against algal growth for more than 10 h while samples with a coating ratio of 25% withstood algae for less than 2 h, indicating the influence of surface roughness. Although the withstanding time of this coating cannot compete with the commercial antifouling coatings, it becomes vital when it comes to the use of this coating as a drag-reducing surface in which fouling worsens the effectiveness.

Interfacial bonding of low-pressure plasma-sprayed Fe-based amorphous coating on 8090 Al–Li alloy

Abstract: ABSTRACT Fe-based amorphous coatings (AMC) are deposited on 8090 Al–Li alloy using low-pressure plasma spraying. Coating’s microstructure and interfacial characteristics are investigated. The coating is mainly amorphous in structure. Some crystalline phases were observed between the two splats. The corrosion current density of this coating is two orders of magnitude less compared to 8090. The coating has high density as the average porosity is less than 0.5%. Because of partial melting and quick cooling of the 8090 alloy in the process of molten droplets deposition, there is an amorphous transition zone formed at the interface of AMC/8090 Al–Li alloy, which indicates localized metallurgical bonding. In electrochemical testing, the coating shows an obvious passivation tendency, and crystallization between splats is the main cause of corrosion. Owing to the low oxygen content, the coating exhibits excellent wear resistance.

Plasma nitriding effects in fatigue behaviour of the welded 4340 steel

Abstract: ABSTRACT Welding is one of the major assembly processes employed in most common aeronautical applications. However, the consequences of the thermal cycle might be detrimental to the material’s fatigue resistance depending strongly on the resulting microstructure. The 4340 steel is known to present temper embrittlement, which greatly reduces its fatigue life and weldability. This work proposes plasma nitriding as an alternative solution to tempering as a post-weld treatment and investigates its effects on material’s hardness and fatigue life. This analysis was complemented by microstructural and fracture surface characterization. Plasma nitriding resulted in the formation of a double layer consisting of a smaller white micrometric nitride layer at the surface and a more diffuse sub-superficial region which led to better fatigue behaviour when compared with the conventional tempering treatment. The achieved higher surface hardness might also be interesting in other applications such as those involving high erosion and wear.

Adhesion of rough cold sprayed metal coatings on polymers

Abstract: ABSTRACT The adhesion strength from the cold-spray coating requires assessing multiple flaws and property distributions. Two approaches have been proposed for determining the adhesion strength of the cold spray-coated substrate. The interfacial shear strength approach combines the fragmentation test with a modified Weibull model. Fragmentation testing can examine materials with geometrical (roughness) and property (strength) variations for cold spray-coated specimens. The results give an insight into local strength and the coating strength distribution. The fracture toughness approach uses an electrical four-point probe to identify crack initiation and calculate the energy release rate of the coating. Sn coatings between 74 and 120 μm show an interfacial shear strength between 25 and 53 MPa and an energy release rate between 15 and 32 J m–2. The measured interfacial shear strength was independent of the coating thickness, while the energy release rate depends on the coating thickness.

Parametric optimisation of plasma polishing process using response surface methodology

Abstract: ABSTRACT The plasma polishing process is one of the non-conventional techniques used to remove material at the atomic level from the substrate. During the polishing of the fused silica substrate, the process parameters, namely radio-frequency (RF) power, pressure ratio (SF6/O2), and total pressure of the plasma chamber, are investigated and optimised for material removal rate (MRR) and % change in surface roughness (% ΔRa ) using response surface methodology. The optimum values obtained for MRR and % ΔRa are 0.012 mm3/min and 3.59, at RF power of 60 W, pressure ratio of 3, and total pressure of 14.3 mbar. The experimental results reveal that surface roughness slightly increases from 0.344 to 0.356 μm after plasma processing at optimised process conditions. Moreover, the plasma-processed fused silica substrate is characterised using field emission scanning electron microscopy and energy dispersive X-ray spectroscopy, which depict the presence of silicon, oxygen, and fluorine on the processed substrate.

Formation of a nanoporous layer on the surface of silver and copper by dealloying of thermal diffusion coatings Me5Zn8 (Me=Ag, Cu) in a deep eutectic solvent

Abstract: ABSTRACT Selective anodic dissolution of pre-galvanized surfaces was used to obtain nano-porous layers of approximately 10 microns thick on copper and silver specimens. To achieve single-phase homogeneous thermal diffusion layers of Cu5Zn8 and Ag5Zn8, we used a zinc plating process carried out in molten eutectic (KCl–NaCl–ZnCl2) at Т = 370°С. Dealloying of these coatings in a deep eutectic solvent (choline chloride/urea + 0.1 mol/l ZnCl2) at T = 133°C produced a typical bi-continuous structure of pores and ligaments (100 nm) on the surface of the silver and the copper. GRAPHICAL ABSTRACT

Corrosion behaviour of facile coated ZnO on Mg–Zn–Zr alloy in Ringer’s physiological solution

Abstract: ABSTRACT Magnesium alloys have received increasing consideration as biodegradable implants owing to their high specific strength, excellent biocompatibility and non-toxicity but their biomedical applications are limited due to low corrosion resistance which can be improved by surface modification and alloying with suitable elements. Various surface modifications of Mg alloys by deposition of different coatings are used to prevent untimely dissolution. This study presents the corrosion behaviour of a thin ZnO coating deposited on a Mg–Zn–Zr alloy by electrophoretic deposition in the Ringer’s solution at 37°C. It was found that the ZnO coating is compact, homogeneous and significantly enhanced its corrosion resistance according to electrochemical test. The polarisation test showed a two orders of magnitude lower current density than that of the bare alloy, while EIS study found a two orders of magnitude greater ZnO coating impedance increasing in bioactivity. The bare specimens showed the development of cracks on the surface whereas the ZnO coated alloy showed no signs of pitting.

Growth characteristics of scanning micro-arc oxidation coating on Ti6Al4V alloy

Abstract: ABSTRACT In this study, the ceramic coating was prepared on Ti6Al4V alloy by scanning micro-arc oxidation (SMAO). The growth features of SMAO coating were investigated by combining the voltage and discharge variation. The result shows that a higher working voltage is obtained during SMAO treatment owing to additional resistance from the electrolyte column. As the SMAO goes on, the discharge region moves to the electrolyte column edge, exhibiting an annular shape. The current density with Gaussian distribution is observed between the stainless-steel tube (cathode) and titanium substrate (anode), which causes the SMAO coating to show a higher thickness in the middle and lower on both sides. Similar to traditional MAO, the SMAO coating has an enhancement in the thickness, pore size and Si content with increasing oxidation time, but coating degradation occurs in the later stage of SMAO. The SMAO coating mainly consists of amorphous SiO2, rutile and anatase phases.

Influence of different modes of microarc oxidation of titanium on the electrochemical properties and surface morphology of the obtained coatings

Abstract: ABSTRACT The influence of Microarc Oxidation (MAO) modes of titanium substrate in electrolytes of the original composition is investigated. Used electrolytes no contain sodium silicate but includes nickel sulphate, sodium aluminate and alkali. The morphology and composition of the obtained coatings were studied by electron microscopy. The electrochemical behaviour was studied using polarisation curves and electrochemical impedance spectroscopy (EIS). Proposed Equivalent circuits are adequately corresponded to experimental EIS data with no more 6% error. The dependence between the elements of the Equivalent circuits and the morphological characteristics depending on the processing is considered. It is shown that MAO coatings on titanium have high corrosion resistance in an aggressive sulphuric acid. The electrochemical properties of coatings undergo irreversible changes in the direction of deterioration after anodic polarisation. It has been established that nickel doping of MAO coatings on titanium does not allow them to serve as anode materials.

Enhanced mechanical properties of molybdenum-coated aluminium via laser cladding

Abstract: ABSTRACT High-quality molybdenum coating has been successfully deposited on the pure aluminium substrate by high-velocity oxygen fuel spraying and subsequent laser remelting and laser cladding process. The microstructure, bonding strength, micro-hardness and wear resistance of the coating were systematically investigated. Results showed that the obtained coating exhibits a good metallurgical bonding interface as well as a dense microstructure with Al8Mo3, AlMo3 and Al5Mo phases, which results in the significant improvement of the mechanical properties of the coating. The bonding strength is increased from 11 ± 1 to 57 ± 4 MPa after laser treatment. Micro-hardness of the coating (480 ± 30 HV) is observed to be increased by about 70% in comparison with the as-sprayed coating (281 ± 8 HV). The wear resistance of the Mo coating was also increased about five to six times by the laser remelting and cladding process.

Energy storehouse and a remarkable photocatalyst: Al2S3/Cu2S/Ni17S18 thin film as supercapacitor electrode and pollutants degradation

Abstract: ABSTRACT Fabrication of the tri metal sulphide Al2S3-Cu2S-Ni17S18 thin film was achieved by physical vapour deposition. The synthesised material was fully characterised by XRD, SEM, EDX, UV-visible spectrophotometer and FTIR. A nanoscale ranged 23.5 nm average crystallite size was obtained for the ternary metal sulphide. A motley of clustered morphological particles was observed by SEM with the confirmation of the desired metals through energy dispersive X-ray. Band gap energy possessed by the ternary metal sulphide was 2.5 eV. The remarkable energy storing capability of the electrode was investigated by cyclic voltammetry, which presented a supercapacitance of 595 F g−1 expressing the pertinence of the synthesised material. Cycling stability of the nanoparticle thin film was also observed through the voltammetric analysis. Furthermore, the environmental applicability of the thin film was investigated by the photocatalytic degradation of pollutants with an impressive degradation rate constant 3.61 × 10−2 min−1 achieved for pesticide.