Effect of Ni Concentration on the Surface Morphology and Corrosion Behavior of Zn-Ni Alloy Coatings

This research work aims to develop electrodeposited Zn-Ni alloy coatings with controlled dissolution tendencies on a mild steel substrate. The varying Ni concentration in the electroplating bath, i.e., 10, 15, 20 and 25 g·L−1, affected the surface morphology and electrochemical properties of the deposited Zn-Ni alloy coatings. SEM and EDS analysis revealed the resulting variation in surface morphology and composition. The electrochemical behavior of different coatings was evaluated by measuring the open circuit potential and cyclic polarization trends in 3.5 wt.% NaCl solution. The degradation behavior of the electrodeposited Zn-Ni coatings was estimated by conducting a salt spray test for 96 h. The addition of Ni in the coating influenced the coating thickness and surface morphology of the coatings. The coating thickness decreased from 38.2 ± 0.5 μm to 20.7 ± 0.5 μm with the increase in Ni concentration. Relatively negative corrosion potential (<−1074 ± 10 mV) of the Zn-Ni alloy coatings compared to the steel substrate (−969 mV) indicated the sacrificial dissolution behavior of the Zn-rich coatings. On the other hand, compared to the pure Zn (26.12 mpy), ~4 times lower corrosion rate of the Zn-Ni coating (7.85 mpy) was observed by the addition of 25 g·L−1 Ni+2 in the bath solution. These results highlighted that the dissolution rate of the sacrificial Zn-Ni alloy coatings can effectively be tuned by the addition of Ni in the alloy coating during the electrodeposition process.

Optimizing Coating Thickness of Electrophoretic Deposition Overlay on Plasma Sprayed YSZ Coating Using Taguchi Method

In this study, nano sized yttria stabilized zirconia (YSZ) suspension in organic solution was deposited by electrophoretic deposition (EPD) method as a protective layer on substrate that was previously plasma sprayed thermal barrier coating (TBCs). In order to improve the performance of TBC from degradation by melt ingression of fuel impurities. Design of experiments (DOE) by Taguchi method was used to optimize the controlled variables of EPD process. A crack free YSZ overlay coating was carried out at different variables; applied voltage (20, 40, 60) V, deposition time (3, 5, 7) min and suspension concentration (5, 10, 15) g/l using DC current. Morphological appearance and cross section of the investigated coating specimen were done using optical and field emission scanning electron microscope. Optimizing process and analysis of variances (ANOVA) were performed by “Minitab 18” software. The results indicate that best condition of coating thickness can be obtained at 40V, 5min and 10g/l when applying signal-to-noise ratio “Larger is better”.

Surface wettability effect of plain and plasma-sprayed copper-coated surfaces on CHF enhancement during saturated pool boiling of FC-72

In the current scenario, CHF study is essential for the safe operation of electronics equipment comprising a two-phase heat transfer process. Therefore, the present experimental investigation involves saturated pool boiling and CHF study of FC 72 over a plain stainless steel surface (SS) and microporous copper-coated SS surfaces under atmospheric conditions. Accordingly, three different plasma-sprayed copper-coated surfaces with coating thicknesses of 65 μm, 105 μm, and 145 μm prepared using micro copper particles of size 25–45 μm. The analysis of the results shows that with an increase in heat flux values, the boiling heat transfer coefficient increases over plain as well as coated surfaces. The plasma-spayed copper-coated surfaces with a coating thickness of 65 μm and 105 μm exhibit a higher boiling heat transfer coefficient as than the plain surface. On the other hand, a 145 μm thick coated surface resulted in a comparable boiling heat transfer coefficient with the plain SS surface. Among the three porous-coated surfaces, the boiling heat transfer coefficient decreases continuously from 65 μm to 145 μm of the coated surface. On the contrary, to the observed nucleate boiling behavior, all the porous-coated surfaces show a higher value of CHF than the plain surface, and the CHF value is found to increase continuously from 65 μm to 145 μm of the coated surfaces. The enhancement of CHF values was found to be 66.29%, 69.17%, and 77.75% for a coating thickness of 65 μm, 105 μm, and 145 μm, respectively, compared with the plain surface. The porous coating thickness of 65 μm shows a greater value of heat transfer coefficient than 105 μm and 145 μm whereas 145 μm exhibits a higher value of CHF as than 65 μm and 105 μm.

Investigation of Biocompatible PEO Coating Growth on cp-Ti with In Situ Spectroscopic Methods

The problem of the optimization of properties for biocompatible coatings as functional materials requires in-depth understanding of the coating formation processes; this allows for precise manufacturing of new generation implantable devices. Plasma electrolytic oxidation (PEO) opens the possibility for the design of biomimetic surfaces for better biocompatibility of titanium materials. The pulsed bipolar PEO process of cp-Ti under voltage control was investigated using joint analysis of the surface characterization and by in situ methods of impedance spectroscopy and optical emission spectroscopy. Scanning electron microscopy, X-ray diffractometry, coating thickness, and roughness measurements were used to characterize the surface morphology evolution during the treatment for 5 min. In situ impedance spectroscopy facilitated the evaluation of the PEO process frequency response and proposed the underlying equivalent circuit where parameters were correlated with the coating layer properties. In situ optical emission spectroscopy helped to analyze the spectral line evolutions for the substrate material and electrolyte species and to justify a method to estimate the coating thickness via the relation of the spectral line intensities. As a result, the optimal treatment time was established as 2 min; this provides a 9–11 µm thick PEO coating with Ra 1 µm, 3–5% porosity, and containing 75% of anatase. The methods for in-situ spectral diagnostics of the coating thickness and roughness were justified so that the treatment time can be corrected online when the coating achieves the required properties.

MATHEMATICAL MODELS OF COATING PROPERTIES UNDER DIFFERENT TECHNOLOGICAL MODES OF PEO

The issue of mathematical modeling of the coating thickness, current and corrosion potential depending on the type of pulsed electrical processing mode, pulse frequency and processing duration is considered.

ENSURING THE SAFETY OF METAL STRUCTURES IN CONSTRUCTION

The author considers the main methods of fire protection for residential and public buildings and structures. The efficiency of metal structures is analyzed, the latest methods of corrosion and fire protection of metal structures are selected. For the plastering, cladding and coating methods, a table of the required thickness in relation to the fire resistance limits was compiled. Based on this table, graphical and empirical dependences for the 30k1 I-beam column are constructed, showing the dependence of temperature on time and the limits of fire resistance on the reduced coating thickness. According to the graphic data, the most economical method of fire protection was chosen, but the resulting deflections exceed the limit according to current standards.

The analyses of frictional losses and thermal stresses in a diesel engine piston coated with different thicknesses of thermal barrier films using co-simulation method

This study comparatively presents the thermal and mechanical effects of different Thermal Barrier Coatings (TBCs) and their thicknesses on the performance of aluminum diesel engine piston by combining Finite Element Analyses (FEA) and Artificial Neural Network (ANN) methods. The piston structure of MWM TbRHS 518S indirect injection six-cylinder diesel engine was modeled. The clustered TBCs (NiCrAlY–Gd2Zr2O7, NiCrAlY–MgO-ZrO2, NiCrAl–Yttria Partially Stabilized Zirconia (YPSZ), and NiCrAlY–La2Zr2O7) were implemented to the related surface of aluminum alloy piston and then static, thermal, and transient structural FEA were conducted for each model. Based on both of the temperature and equivalent stress distributions, NiCrAlY–Gd2Zr2O7 coated model displayed the best performance. Additionally, the effects of top coating thicknesses of TBCs were investigated in the range of 0.1–1.0 mm with 0.1 mm increments in FEAs. The thermally effective top coating thickness was predicted as 0.95 mm for the selected TBC using ANN method. Then the effects of coating thickness on frictional performance were revealed by generating transient structural FE models and utilizing stribeck diagram. The uncoated and 0.95 mm NiCrAlY–Gd2Zr2O7 coated models were adjusted as transient and the related crank angle – dependent in-cylinder combustion pressure data was implemented. The friction force was reduced by at least 15% in NiCrAlY–Gd2Zr2O7 coated model.