High-quality Coatings Research Articles

Production of Transitional Diffused Layers by Electrospark Coating

The article presents a new method for production of diffused transitional layers with nano- and microthickness by local removal of nanofilms on aluminum alloys. This allows procuring of high-quality coatings on fusible alloys (for example, on aluminum ones) by materials, the melting point of which is 2-3 times higher than that of the basis (for example, of cast iron). This permits imparting new useful properties to workpieces made from light alloys with decent values for electrochemical working. The authors show that application of coatings provides minimum heating of workpieces. This enables the regulation in temperature condition of operating environment and permits efficiency improving during the process of electrochemical working by means of higher density current supply.

Mechanical and microstructural characterization of MCrAlY coatings produced by laser cladding: The influence of the Ni, Co and Al content

Laser metal deposition (LMD) and laser cladding (LC) are alternative methods to thermal spraying processes to produce dense, high-quality coatings. In this work, two MCrAlY coatings (M = Ni + Co) have been prepared onto stainless steel substrate using a coaxial LC technique under two different Ni/Co and Al proportions. The mechanical properties were then evaluated with microhardness, nanoindentation, and three-point bending tests. The microstructure and composition of coatings were characterized by X-ray Diffraction (XRD) analysis and Field Emission Electron Microscopy (FESEM) coupled to an Energy Dispersive Spectroscopy (EDS) detector. The study revealed that the γ/β phases formed in the MCrAlY coating microstructure result in a lower elastic modulus than the austenitic stainless steel substrate, while an inverse behavior for hardness was observed due the presence of the aluminum-rich β-phase. Under flexural loads, the failure of coatings showed plasticity and anisotropy characteristics depending on the two laser tracks orientations evaluated.

EPD of Novel Nanostructured Silica Coatings: Processing and Applications

Specific designed silver-doped glazes have already been used for antimicrobial coating applications in ceramic consumer oriented industry; however, comprehensive use of silver-based agents in ceramic glazes presents issues of clouding, crazing, discoloration, and other undesirable consequences to the glaze aesthetics as well as severe cost problems. Accordingly, there is a need for low-cost and high quality glazes and coatings that offer persistent built-in antimicrobial protection. Here we show that electrophoretic deposition, based on membrane templating, may answer these requests of realization of micro-topological design of glazings, while offering at the same time a wide library of available antimicrobial efficient nanomaterials to be incorporated into the micro-structured glazes. As consequence, these coatings are particularly suited for applications where interaction with pathogens in liquid solutions or gas-phase atmospheres has to be favoured. Strategies on the integration of microstructured coatings into devices with applicative purposes in consumer ceramics and sanitary ware products, are presented.

Roughness Reduction of Large-Area High-Quality Thick Al Coatings for Large-Size Echelle Gratings by Chemical Mechanical Polishing

Roughness Reduction of Large-Area High-Quality Thick Al Coatings for Large-Size Echelle Gratings by Chemical Mechanical Polishing

Molecular dynamics simulations of lattice site preference and phase separation in B2-NiAl with Pt addition

Pt-modified β-NiAl is an alloy of special interest for bond coatings in the hot sections of the engines. Nevertheless, the site occupancy of Pt is still an open issue. In this work, we have constructed a Ni-Al-Pt interatomic potential and carried out the molecular dynamics simulations to reveal the atomic structures and displacement behaviours of Pt in B2-NiAl. The results of the simulations not only show that the Pt atoms have a strong preference for the Ni site in B2-NiAl but also suggest that an increasing Pt concentration leads to a more pronounced displacement of the Al atoms. Moreover, the simulations predict the occurrence of phase separation in B2-NiAl when the Pt concentration reaches 20%, which is confirmed in the subsequent experiments by the formation of a β-NiAl+Al2Pt dual-phase structure. The present findings promote the understanding of the atomic structures in B2-NiAl, which in turn may provide useful guidance for the fabrication of high-quality β-NiAl bond coatings.

Thermal-induced blister cracking behavior of annealed sandwich-structured TiN/CrAlN films

Sandwich-structured TiN/CrAlN films were rationally designed using metallic Ti and Al-Cr alloy targets by RF-pulsed magnetron sputtering. After obtained films were annealed at diverse temperatures at atmospheric pressure for 1h, the hardness reveals an apparent decrease evolution from 29.2 to 15.7GPa and H/E* ratio declines below 0.1 with increasing annealing temperature. Meanwhile, the grain size gradually becomes larger from 16.3 to 130.0nm with increasing annealing temperature. Interestingly, it is observed that cracking behavior of sandwich-structured composite TiN/CrAlN films at elevated temperature is originated from the top of the blisters where main component is alumina on the surface, in virtue of intrinsically induced stress during oxidation, thermal expansion mismatch and phase transformation of the oxide layer. No cracks, nevertheless, are yielded in the film between any two blisters. Herein, these findings provide some beneficial references for preparing high quality films and coatings in high temperature service.

Synthesis and Study of Organosoluble Aromatic Cardo (co)polyamides and Their Application in the Optical Fiber Primary Coating Technology

A series of organosoluble aromatic cardo copolyamides (PA) with chlorine and carboxylic side groups has been synthesised by low‐temperature polycondensation in N‐methyl‐2‐pyrrolidone (N‐MP) solution and their properties have been estimated. The obtained polymers are differed in high molar masses (ηinh = 0.7 ÷ 1.8 dL/g) and demonstrate the following thermal characteristics: 300 °C < Tg < 390 °C; 425 °C < T10% < 510 °C (in air). PA films are characterized by high tensile strength (100 ÷ 230 MPa) and modulus (1.6 ÷ 2.3 GPa). It was stated the obtained PAs form the high quality coatings with good adhesion to the optical fiber surface without any additional coupling agent. The fibers with elaborated PA coatings demonstrate high thermal stability. The study of the optical fiber bending strength before and after thermal tests has shown that this parameter decreases by 10% only after prolonged exposure to high temperatures, namely, 72 h at 200–300 °C. Some samples withstand more than 1 h treatment at 350 °C without any changes of the optical fiber bending strength.

Diffusion Saturation by Titanium from Liquid-Metal Media as Way to Increase Carbide-Tipped Tool Life

The analysis of the strengths and weaknesses of the existing technologies aimed at improving the performance properties of carbide-tipped tools is presented. The results of studies into the process of diffusion metallization by titanium of a carbide-tipped tool TK type from the media of fusible liquid-metal solutions is given. The influence of titanium diffusion coatings on the durability of carbide tools is investigated. A method of providing formation on hard alloys for wear-resistant titanium high-quality functional coatings is described. The thickness of the coating varies depending on the temperature and exposure time, and ranges from 4 to 6 μm. The hardness of the coatings obtained depends on the temperature of the coating and modes of pre-carburizing, and varies from 24100 to 30000 MPa. The microstructure of the coatings is investigated. The coating consists of two layers: the coating and the transition zone, the size and hardness of which depends on the conditions of pre-carburization and modes of application of the coating. The dependence of the coatings thickness on the duration of the plates exposure in the melt, the temperature of coating composition from the coated hard alloy is investigated.

Diamond thin films: giving biomedical applications a new shine.

Progress made in the last two decades in chemical vapour deposition technology has enabled the production of inexpensive, high-quality coatings made from diamond to become a scientific and commercial reality. Two properties of diamond make it a highly desirable candidate material for biomedical applications: first, it is bioinert, meaning that there is minimal immune response when diamond is implanted into the body, and second, its electrical conductivity can be altered in a controlled manner, from insulating to near-metallic. In vitro, diamond can be used as a substrate upon which a range of biological cells can be cultured. In vivo, diamond thin films have been proposed as coatings for implants and prostheses. Here, we review a large body of data regarding the use of diamond substrates for in vitro cell culture. We also detail more recent work exploring diamond-coated implants with the main targets being bone and neural tissue. We conclude that diamond emerges as one of the major new biomaterials of the twenty-first century that could shape the way medical treatment will be performed, especially when invasive procedures are required.

Preparation and Characterization of Soybean Oil-Based Polyurethanes for Digital Doming Applications.

Polyurethane-resin doming is currently one of the fastest growing markets in the field of industrial graphics and product identification. Semi-rigid bio-based polyurethanes were prepared deriving from soybean oil as a valuable alternative to fossil materials for digital doming and applied to digital mosaic technology. Bio-resins produced can favorably compete with the analogous fossil polymers, giving high-quality surface coatings (ascertained by SEM analyses). In addition, polyurethane synthesis was accomplished by using a mercury- and tin-free catalyst (the commercially available zinc derivative K22) bringing significant benefits in terms of cost efficiency and eco-sustainability.

Influence of ion bombardment of a substrate on the quality of vacuum-plasma Ti-TiN coatings

The characteristics of the quality of multi-layer vacuum ion-plasma coatings Ti-TiN such as roughness and adhesion strength are investigated. It is shown that additional ion bombardment promotes the production of high-quality coatings. Ion bombardment has a significant effect on the state of the surface layer of the metal. In the process of ion bombardment, conditions are created for the formation of active adsorption centers and the formation of a fine-grained structure, nanoscale grains and layers.

Film thickness effect on texture and residual stress sign transition in sputtered TiN thin films

Abstract Residual stress in thin films and coatings strongly affects their properties and behavior in service. Comprehensive understanding and precise measurements of residual stress are prerequisites for preparing high quality films and coatings. Residual stresses in TiN films with different thickness were measured by X-ray diffraction (XRD) employing the cos 2 α sin 2 ψ method with certain optimization. Grazing incidence parallel beam optics was combined with side-inclination geometry using in-house designed sample stage to ensure results accuracy. To validate this method, TiN films with thickness ranging from 1 to 3 µm were deposited on (100) Si single crystal substrates at 300 °C by RF magnetron sputtering. High compressive −2 GPa residual stress was present in the 0.9 µm thick film and decreased with film thickness. Tensile stress of less than 0.3 GPa was present in 2 µm TiN film. Compressive-to-tensile residual stress transition was observed with the film thickness increase. Microstructure change with growth, annihilation of grain boudaries, atomic peening and recovery mechanisms are responsible for the reported stress sign transition.

Multifunctional Ti-O coatings on polyethylene terephthalate fabric produced by using roll-to-roll high power impulse magnetron sputtering system

Functional and comfortable textiles have been widely used for outdoor protective garment against outer moisture, wind, and cold, combined with good perspiration transport from the inside to the outside. Hydrophobic textiles have attracted various applications, such as water proof, self-cleaning, and bioactive properties, whereas the hydrophilic textiles show wettability, air permeability, wicking, and silk-like appearance. Ti-O coatings have been found in a wide range of applications. Among coating techniques used to deposit Ti-O thin films, high power impulse magnetron sputtering (HIPIMS) has attracted a great deal of attention recently due to high plasma density provided to form a strongly adhered film at a relatively low substrate temperature. In this study, a roll-to-roll high power impulse magnetron sputtering (R2R-HIPIMS) system to produce multifunctional Ti-O coatings on polyethylene terephthalate (PET) fabric substrate was used, which takes advantage of large-scale production and high-quality coatings. Results indicate that the TiO coated PET fabric exhibited the hydrophobic property with a water contact angle of 119o, while TiO2 coated PET fabric showed the hydrophilic property with a water contact angle of 37o. Ti-O coated PET fabrics show high color fastness and effectively block solar heat, indicating that the R2R-HIPIMS is a promising continuous sputtering process in fabricating hydrophobic-TiO/fabric/hydrophilic-TiO2 for applications in multifunctional textiles.

Supersonic Plasma Spray Deposition of CoNiCrAlY Coatings on Ti-6Al-4V Alloy

Plasma spray is a versatile technology used for production of environmental and thermal barrier coatings, mainly in the aerospace, gas turbine, and automotive industries, with potential application in the renewable energy industry. New plasma spray technologies have been developed recently to produce high-quality coatings as an alternative to the costly low-pressure plasma-spray process. In this work, we studied the properties of as-sprayed CoNiCrAlY coatings deposited on Ti-6Al-4V substrate with smooth surface (R a = 0.8 μm) by means of a plasma torch operating in supersonic regime at atmospheric pressure. The CoNiCrAlY coatings were evaluated in terms of their surface roughness, microstructure, instrumented indentation, and phase content. Static and dynamic depositions were investigated to examine their effect on coating characteristics. Results show that the substrate surface velocity has a major influence on the coating properties. The sprayed CoNiCrAlY coatings exhibit low roughness (R a of 5.7 μm), low porosity (0.8%), excellent mechanical properties (H it = 6.1 GPa, E it = 155 GPa), and elevated interface toughness (2.4 MPa m1/2).

IZO deposited by PLD on flexible substrate for organic heterostructures

In:ZnO (IZO) thin films were deposited on flexible plastic substrates by pulsed laser deposition (PLD) method. The obtained layers present adequate optical and electrical properties competitive with those based on indium tin oxide (ITO). The figure of merit (9 × 10−3 Ω−1) calculated for IZO layers demonstrates that high quality coatings can be prepared by this deposition technique. A thermal annealing (150 °C for 1 h) or an oxygen plasma etching (6 mbar for 10 min.) were applied to the IZO layers to evaluate the influence of these treatments on the properties of the transparent coatings. Using vacuum evaporation, organic heterostructures based on cooper phthalocyanine (CuPc) and 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) were deposited on the untreated and treated IZO layers. The optical and electrical properties of the heterostructures were investigated by UV–Vis, FTIR and current–voltage (I–V) measurements. For the heterostructure fabricated on IZO treated in oxygen plasma, an improvement in the current value with at least one order of magnitude was evidenced in the I–V characteristics recorded in dark conditions. Also, an increase in the current value for the heterostructure deposited on untreated IZO layer can be achieved by adding an organic layer such as tris-8-hydroxyquinoline aluminium (Alq3).

Suspension medium’s impact on the EPD of nano-YSZ on Fecralloy

Electrophoretic deposition (EPD) was employed to coat yttria-stabilised zirconia (YSZ) on Fecralloy. Various non-aqueous solvents were utilised to achieve smooth crack-free YSZ coatings. The EPD parameters, including solvent type, sedimentation height, zeta potential, particle size, pH and deposition weight, were studied. The micro-structural evolution and mechanical properties of the coatings were studied by the field emission scanning electron microscopy and micro-hardness, respectively. It was found that coatings obtained from 0.4 g L−1 I2 acetyl–acetone were uniform, smooth and crack free. Also they had narrow particle size distributions and higher zeta potential in the suspension. The experimental results revealed that suspension stability was a requirement for obtaining high-quality coatings and deposition yield for stable suspensions was higher; however, particle coagulation resulted in coatings with low green density and poor sinter ability. A transition in deposition mechanism from linear to parabolic was observed during EPD where deposition rate was decreased by time.

Composite coatings prepared by combined plasma electrolytic oxidation and chemical conversion routes on magnesium-lithium alloy

Abstract Various strategies for the elimination of inherent defects from plasma electrolytic oxidation (PEO) coatings are being developed for practical applications. In this regard, two types of composite coatings were introduced via PEO treatment followed by chemical conversion approach on a magnesium-lithium alloy (Mg-Li alloy). Detailed morphologies and compositions of the composite coatings were studied by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), and thin-film X-ray diffraction (TF-XRD). Barrier properties of the composite coatings were evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The results demonstrate that this two-step approach improves the anti-corrosion performance of the composite coatings for protection of the Mg-Li alloy. Specifically, the stannate composite coating exhibits enhanced corrosion resistance and impressive long-term stability relative to the composite coating prepared in cerium and lanthanum conversion solution. Our method allows the simple, efficient, and cost-effective fabrication of high-quality composite coatings based on a combined PEO and chemical conversion process on Mg-Li alloys, and therefore it holds great promise for a wide range of applications where corrosion resistance is vital.

Microstructural evolution of cold-sprayed Inconel 625 superalloy coatings on low alloy steel substrate

This study illustrates microstructural evolution of INCONEL 625 superalloy coatings cold-sprayed on a 4130 chrome alloy steel with medium carbon content. INCONEL 625 powder (5–25 μm) were successfully cold sprayed without any oxidation. The comprehensive microstructure analysis of the as-sprayed coatings and of the substrate-coating interface was carried out using EBSD, TEM, and XRD. The coating microstructure at the substrate-coating interface was markedly different from the microstructure away from the interface. The coating microstructure at steel-coating interface consisted of a fine layer of small grains. The microstructure beyond this fine layer can be divided into splats, inter splat and intra splat boundaries. Both splat and splat boundaries exhibited deformation induced dislocations. Dynamic recovery of dislocations-ridden regions inside the splat was responsible for the development of sub grain structure inside a splat with both low and high angle grain boundaries. Splat-splat (inter splat) boundary consisted of a relatively high density of dislocations and shear bands as a result of adiabatic shear flow localisation. This flow instability is believed to enhance the microstructural integrity by eliminating porosity at splat-splat boundaries. Based on the microstructural analysis using electron microscopy, a plausible mechanism for the development of microstructure has been proposed in this work. Cold spray technique can thus be deployed to develop high quality coatings of commercial importance.

Macroparticles formation in cathodic arc deposition of nitride coatings from TiNb alloy cathodes

Reduction of macroparticles embedded within the cathodic arc deposited coatings is important for achieving high quality coatings with superior tribological properties, and it remains a major challenge in cathodic arc depositions. In the present study, the authors aim to understand the nature of macroparticles formed from TiNb alloy cathodes and the role of TiNb cathode nitridation in reducing the amount of generated macroparticles. The microstructure of the macroparticles was investigated using scanning transmission electron microscopy-energy dispersive spectroscopy, scanning electron microscopy, and x-ray diffraction techniques and revealed compositionally different macroparticles, such as macroparticles with a Nb-rich core, Ti-rich macroparticles, and macroparticles with a composition similar to that of the coatings. The examination of the macroparticles indicated the compositional segregation of niobium and titanium. With increasing N2 gas pressure during deposition, the macroparticles showed increased nitridation while the density of macroparticles within the coating was slightly diminished.

Influence of Mo on the structure and the tribomechanical properties of arc evaporated Ti-Al-N

Today's industrial forming and machining processes of various materials, require precision and efficiency. A continuous improvement in wear resistance and mechanical properties of protective coatings is therefore a key factor for many applications. Especially, molybdenum (Mo) is a promising candidate to further improve the tribological properties of industrially high-quality coatings like Ti-Al-N. Therefore, we study the influence of Mo on the phase formation, mechanical properties, as well as wear performance of cathodic arc evaporated Ti1−x−yAlxMoyN hard protective coatings. According to our results, we can neither confirm nor rule out a solubility limit for molybdenum up to 12at.% Mo and bias potentials Ubias between −40 and −120V. With increasing Mo content, the deposition rate increases―basically due to the increased evaporation rate of the powder metallurgically prepared (Ti0.5Al0.5)1−yMoy cathodes. For bias potentials of −80 and −120V, the hardness is 36.6±1.0 and 39.0±0.6GPa, respectively, and almost independent of the Mo content. But the wear rate significantly decreases with increasing Mo content by two orders of magnitude (from 3.0·10−5mm3/Nm for Ti0.56Al0.44N to ≤2.1 10−7mm3/Nm for Ti0.50Al0.38Mo0.12N), accompanied by a reduction of the coefficient of friction from 1.0 to 0.5, respectively. Consequently, Ti1−x−yAlxMoyN coatings are superior in tribomechanical properties and wear performance to conventional Ti0.56Al0.44N.