Coatings

In this study, the effect of a thermal barrier coating with yttria-stabilized zirconia (YSZ) and aluminum silicate (Al₂O₃·SiO₂) alongside an NiCrAl bond coat on the engine performance and emission analysis was evaluated by using conventional diesel and pure palm oil biodiesel. These materials were coated on the piston alloy via plasma spray coating. The findings demonstrated that YSZ coating presented better engine performances, in terms of brake thermal efficiency (BTE) and brake-specific fuel consumption (BSFC) for both fuels. The piston with YSZ coating materials achieved the highest BTE (15.94% for diesel, 14.55% for biodiesel) and lowest BSFC (498.96 g/kWh for diesel, 619.81 g/kWh for biodiesel). However, Al₂O₃·SiO₂ coatings indicated better emission with lowest emissions of NO, CO, and CO₂ for both diesel and biodiesel. For the uncoated piston, the results indicated that the engine clocked the highest torque and power, especially on diesel fuel due to the high viscosity and low caloric value, and it recorded the lowest hydrocarbon emission due to the complete combustion of fuel in the engine. Hence, it was concluded that the YSZ coating could lead to better engine performance, while Al₂O₃·SiO₂ showed promising results in terms of greenhouse gas emission. Full article

In the present work, we had the opportunity to study the coating systems of three different coeval violins, namely “Spagnoletti”, “Stauffer”, and “Principe Doria”, made by Giuseppe Guarneri “del Gesù” in 1734. These three violins were non-invasively investigated by reflection Fourier transform infrared spectroscopy and X-ray fluorescence. These two techniques were combined for the first time with a 3D laser scanner. The analytical campaign enabled the characterization of the materials and their distribution within the stratigraphy, mainly composed of varnish and, when present, of a proteinaceous ground coat. Some restoration materials were also identified, suggesting the application of different maintenance treatments undertaken during their history. The preliminary information about morphological and geometrical differences between the three coeval violins were acquired through the 3D laser scanner in order to observe similarities and differences in the design features among the three violins. Full article

Mo and Mo-based alloys are important aerospace materials with excellent high temperature mechanical properties. However, their oxidation resistance is very poor at high temperature, and the formation of volatile MoO₃ will lead to catastrophic oxidation failure of molybdenum alloy components. Extensive research on the poor oxidation problem has indicated that the halide activated pack cementation (HAPC) technology is an ideal method to solve the problem. In this work, the microstructure, oxide growth mechanism, oxidation characteristics, and oxidation mechanism of the HAPC coatings were summarized and analyzed. In addition, the merits and demerits of HPAC techniques are critically examined and the future scope of research in the domain is outlined. Full article

Doping impurity into ZnO is an effective and powerful technique to tailor structures and enhance its optical properties. In this work, Zn_1−xMg_xO and Zn_1−x−yMg_xB_yO nanoparticles (x = 0, 0.1, 0.2, 0.3, 0.4; y = 0, 0.02, 0.04) were synthesized via one-pot method. It shows that the Mg and B dopants has great influence on crystallinity and surface morphology of ZnO nanoparticles, without changing the wurtzite structure of ZnO. The band structure study indicates that the competition of Conductive Band (CB) shift, Burstein–Moss (B-M) shift and Shrinkage effect will cause the band gap energy change in ZnO. Full article

By employing carbon dioxide as one source of reaction gases, carbon-doped Ti–O films were fabricated via reactive magnetron sputtering deposition. The chemical bonding configurations and microstructure of the films were analyzed by Raman spectrum and SEM, respectively. The effect of pH on the photocatalytic activities of the films was determined via evaluation of the decolorization rate of methyl orange under alkali, acid and neutrality conditions using UV light irradiation. Electrochemical impedance spectroscopy and potentiodynamic polarization tests were employed to determine the anti-corrosion properties. Compared with the C-free Ti–O film, the C-doped Ti–O films exhibit superior corrosion resistance. Furthermore, the results of the photodegradation experiment suggest that the C-doped Ti–O films have excellent photocatalytic activities and, for methyl orange, those with higher carbon content exhibit hyper-photodegradative effect under the alkali condition. Full article

Protective coating is an effective way to extend materials’ high-temperature service life. In order to improve the high-temperature oxidation resistance of AISI 304 stainless steel, mullite films with different layers were successfully prepared by the sol-gel method and the sintering process on the surface of stainless steel. The effect of the film layers on the high-temperature oxidation resistance of stainless steel at 900 °C for 100 h was studied. The analysis results of oxidation kinetics, X-rays diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive analysis (EDS) show that Al_1.4Si_0.3O_2.7 mullite film effectively improved the high-temperature oxidation resistance of stainless steel. The sample with three-layer mullite film has the best high-temperature oxidation resistance. The mass gain and oxidation spalling mass are only 4.6% and 34.5% of those of the uncoated sample after 100 h cyclic oxidation at 900 °C. A chromium oxide layer was formed at the interface of mullite film and the substrate during the sintering process. The generation of selective Cr₂O₃ scale was promoted at the cyclic oxidation stage so that the sample with three-layers has excellent high-temperature oxidation resistance. Full article

Thermally sprayed ceramic coatings are applied for the protection of surfaces that are exposed mainly to wear, high temperatures, and corrosion. In recent years, great interest has been garnered by spray processes with submicrometric and nanometric feedstock materials, due to the refinement of the structure and improved coating properties. This paper compares the microstructure and tribological properties of alumina coatings sprayed using conventional atmospheric plasma spraying (APS), and various methods that use finely grained suspension feedstocks, namely, suspension plasma spraying (SPS) and suspension high-velocity oxy-fuel spraying (S-HVOF). Furthermore, the suspension plasma-sprayed Al₂O₃ coatings have been deposited with radial (SPS) and axial (A-SPS) feedstock injection. The results showed that all suspension-based coatings demonstrated much better wear resistance than the powder-sprayed ones. S-HVOF and axial suspension plasma spraying (A-SPS) allowed for the deposition of the most dense and homogeneous coatings. Dense-structured coatings with low porosity (4 vol.%) and good cohesion to the metallic substrate, containing a high content of α–Al₂O₃ phase (56 vol.%) and a very low wear rate (0.2 ± 0.04 mm³ × 10⁻⁶/(N∙m)), were produced with the S-HVOF method. The wear mechanism of ceramic coatings included the adhesive wear mode supported by the fatigue-induced material delamination. Moreover, the presence of wear debris and tribofilm was confirmed. Finally, the coefficient of friction for the coatings was in the range between 0.44 and 0.68, with the highest values being recorded for APS sprayed coatings. Full article

Electromagnetic riveting process (EMR) is a high-speed impact connection technology with the advantages of fast loading speed, large impact force and stable rivet deformation. In this work, the axisymmetric sequential and loose electromagnetic-structural coupling simulation models were conducted to perform the electromagnetic riveting process of a Ti-6Al-4V titanium rivet, and the parameter analysis of the riveting setup was performed based on the sequential coupled simulation results. In addition, the single-objective optimization problem of punch displacement was conducted using the Hooke–Jeeves algorithm. Based on the adaptive remeshing technology adopted in air meshes, the deformation calculated in the structural field was well transferred to the electromagnetic field in the sequential coupled model. Thus, the sequential coupling simulation results presented higher accuracy on the punch speed and rivet deformation than the loose coupling numerical model. The maximum relative difference of electromagnetic force (EMF) on driver plate and radial displacement in the rivet shaft was 34.86% and 13.43%, respectively. The parameter analysis results showed that the outer diameter and the height of the driver plate had a significant first-order effect on the response of displacement, while the platform height, transition zone height, angle, and transition zone width of the amplifier presented a strong interaction effect. Using the obtained results on the optimal structural parameters, the punch speed was effectively improved from 6.13 to 8.12 m/s with a 32.46% increase. Furthermore, the displacement of the punch increasing from 3.38 to 3.81 mm would lead to an 80.55% increase in the maximum radial displacement of the rivet shaft. This indicated that the deformation of the rivet was efficiently improved by using the optimal rivet model. Full article

Near- and mid-infrared optical coherence tomography (OCT) is evaluated as a non-destructive and non-contact reflection imaging modality for inspection of industrial and marine coatings. Near-infrared OCT was used to obtain high-resolution images (~6/2 µm lateral/axial) of hidden subsurface cracks and defects in a resin base coating, which had been exposed to high pressure and high temperature to study coating degradation in hostile environments. Mid-infrared OCT was employed for high-resolution (~15/8.5 µm lateral/axial) subsurface inspection of highly scattering marine coatings, demonstrating monitoring of wet film thickness and particle dispersion during curing of a 210 µm layer of antifouling coating, and detection of substrate corrosion through 369 µm of high-gloss alkyd enamel. Combining high-resolution and fast, non-invasive scanning, OCT is therefore considered a promising tool for studying coating performance and for industrial inspection. Full article

Up to now, there have been no complete theoretical researches and field experiment reports on the fiber fusion loss at high altitude. Therefore, we have conducted an exploratory study on the fiber splicing loss at high altitude, and firstly analyze the influence of mode field diameter mismatch, axial offset, angle tilt or end face gap affected by high altitude on splice loss, and then discuss the influence of fusion-splicing parameters on splice loss. Besides, a mathematical model for reducing the splicing loss of single-mode fiber at high altitude is established by combining the effects of temperature, humidity, oxygen content, atmospheric pressure, gale and gravity. We have conducted repeated field fusion experiments in different altitude areas (53, 2980, 4000, 4200, 4300, 5020, and 5200 m) more than once, hence obtaining a large number of field experimental data, making a deep comparison between typical “plain” area and typical “high altitude” area. The splice loss of most fusion points achieved successfully has been reduced by at least 0.07 dB. The simulation results are basically consistent with the theoretical analysis. Ultimately, the method proposed has been directly applied to on-site splicing engineering in high altitude environment and achieves good results. Full article

Objectives: This study aimed to measure non-destructively gold (Au) electrodeposited on a high-gold alloy by modulating coating time and comparing this to sputtering Au to known thicknesses. Methods: Au was electrodeposited (plated) on 11 high-gold alloy plates (A–K) at 2.8V between 20 and 220 min. Seven Au strips were sputter coated on the same alloy to known thicknesses (range 50–500 nm). Energy dispersive X-ray spectroscopy (EDS) was used to measure minimal electron energy (E₀) required to penetrate Au coatings and generate x-ray signals of 1% atomic palladium (Pd) from the underlying alloy for test samples and Au strips. % Pd X-ray concentration at maximum 30 kV was also obtained. The obtained signal–thickness relationship of known Au strip thicknesses was used to calculate Au thickness on the A–K samples based on two analytical relations. Energy dispersive X-ray fluorescence spectroscopy (XRF) was used as a complementary method to ensure coating thickness estimations were accurate. Results: EDS values for all reference and unknown thicknesses were obtained and verified with XRF. Correlating these signals with the Data Analysis Software and matching with known plating times allowed estimation of Au thickness of the unknown samples (range 27–425 nm). Estimated thicknesses were shown to have a linear relationship with plating time except for samples C–D, where there was an inverted relationship. Significance: A non-destructive method for measuring electrodeposited thickness of Au on high-gold alloys related to plating time was developed and verified. There is a linear relationship to Au thickness and plating time between 20 and 220 min. Full article

Chromium-carbon films were deposited by utilizing reactive high-power impulse magnetron sputtering with different mixture ratios of ethyne and argon with a constant deposition total pressure while the deposition temperature, pulse frequency, duty cycle and average power of the chromium cathode remain the same. The microstructure and chemical bonding of the obtained films within different composition were compared. The results show that with the increasing ethyne ratio, the carbon content in films increases linearly with two slopes. Moreover, the microstructure of the deposited film changes from a dense glassy structure into a columnar structure, even a clusters structure. The sp2-C bonding in films decreases but the Cr–C bonding increases with decreasing the ethyne ratio. This reveals the main phase of films changes from a hydrogenated amorphous carbon phase into a glassy amorphous chromium carbide phase. Such changes of the microstructure and phase cause a large difference on the film hardness and elasticity. Full article

Tungsten trioxide (WO₃) is used to prepare the important electrochromic layer of the electrochromic device as a wide bandgap semiconductor material. In this study, WO₃ electrochromic film was successfully prepared by screen printing. To modify the thixotropy and wettability of the ink, polyvinyl alcohol (PVA) and 2-perfluoroalkyl ethanol (FSO) were added in the ammonium meta-tungstate (AMT) solution. We found that the PVA additive could improve the dynamic viscosity of the solution and modify the uniformity of the film. 2-Perfluoroalkyl ethanol (FSO) could lower the surface tension and increase the wettability of the AMT solution on the substrate. By observing the morphology of the printed films, the ink formulas for screen printing were selected. We found the annealing process could help remove PVA. Through characterization of electrochromic performance, it was found that the best performing device had 42.57% modulation and 93.25 cm²·C⁻¹ coloration efficiency (CE) for 600 nm light. This study showed great potential in the preparation of WO₃ electrochromic devices by a low-cost screen-printing method. Full article

In this paper, a plasma-induced hemi-wicking phenomenon observed on hydrophobic sanded polymer surfaces, polypropylene (PP), polyethylene terephthalate (PET) and polyethylene (PE) is reported. An atmospheric-pressure argon plasma jet was used to treat a limited area of the carefully sanded polymer surfaces to induce the hemi-wicking phenomenon. Such hemi-wicking triggered by the plasma activation is different from the traditional type, which is achieved purely by the surface topography. Surface analyses by X-ray photoelectron spectroscopy (XPS) and water contact analysis (WCA) show that the combination of sanding and plasma treatment increased the oxygen-to-carbon ratio, which is highly beneficial for surface hydrophilicity. The shear stress tests show that the combination of sanding and plasma treatment can enhance the shear stress by 125%, 95%, and 296% on PP, PET, and PE, respectively. The study shows that the newly developed technique by combining the sanding and plasma processing for polymers could be a potentially useful method in future industry applications. Full article

The effects of thermal aging time at 400 °C on the microstructure and mechanical and corrosion behaviors of Z3CN20.09M cast stainless steel were investigated; and the corresponding thermal aging mechanism was studied. It was revealed that the changes in mechanical properties after thermal aging were mainly caused by the iron-rich phase (α) and the chromium-rich phase (α’) produced by the amplitude-modulation decomposition of ferrite. A similar trend of thermoelectric potential during thermal aging was determined in relation to the Charpy impact energy. However, the corrosion resistance of Z3CN20.09M cast stainless steel deteriorates as thermal aging time increases. When the thermal aging is longer than 3000 h, the precipitation of G phase has a great influence on the corrosion resistance. The interfacial matching relationship between G phase and the surrounding ferrite was established by selected area electron diffraction of HRTEM. The relationship is of cube-on-cube phase boundary type. The impact fracture mechanisms in relation to thermal aging time were also studied and compared. Full article

Yb₂Si₂O₇/Si environmental barrier coatings (EBCs) were produced by air plasma spray (APS) and low-pressure plasma spray (LPPS) processes. The phase composition, microstructure, and bonding strength of APS and LPPS EBCs were investigated. Thermal cycling tests were performed in air and in steam atmosphere respectively at 1316 °C for both APS and LPPS EBCs. There is no coating failure in air atmosphere for both APS and LPPS EBCs after 900 cycles. In contrast, APS EBCs have an average life of 576 cycles in a steam cycling test in 90% H₂O + 10% air at 1316 °C while LPPS EBCs survived 1000 cycles without failure. The superior durability of the LPPS EBCs compared to APS EBCs in the same steam cycling environment is attributed to the significantly reduced thermally grown oxide (TGO) growth rate because of the denser and crack-free microstructure, higher bonding strength, and reduced coefficient of thermal expansion (CTE) mismatch (less Yb₂SiO₅ phase) in the LPPS Yb₂Si₂O₇/Si EBCs. Full article

This study describes the performance of nanoscale multilayer TiN/NbN coatings deposited on CoCrMo medical-grade alloys by utilising novel mixed high power impulse magnetron sputtering (HIPIMS) and direct current unbalanced magnetron sputtering (UBM) technique in an industrial size vacuum coater. Scanning electron microscopy analysis showed that these coatings were extremely dense without any intercolumnar voids. The coating exhibited high hardness of 28 GPa, as well as low friction and wear coefficient of 0.7 and 1.4 × 10⁻¹⁴ m³·N⁻¹·m⁻¹, respectively, as compared to the bare material. Scratch tests revealed superior coating to substrate adhesion due to the HIPIMS etching prior to coating deposition. Energy-dispersive X-ray analysis of the wear debris generated during the impact test together with focused ion beam cross-section analysis in different locations of the impact crater revealed the coating failure mechanism and further confirmed the excellent coating to substrate bonding strength. Potentiodynamic polarisation tests in NaCl and Hank’s solutions revealed the clear passivation behaviour, several orders of magnitude lower corrosion currents, and high pitting potentials of the coating, which guarantee excellent protection to the base alloy in such aggressive environments. Inductively coupled plasma mass spectrometry analysis of Hank’s solution containing corrosion debris of the coated sample revealed that the leaching of harmful metal ions from the base material was reduced to below the detection limit of the technique, thus demonstrating the high barrier properties of the coating. Full article