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”.

Investigations of sintering temperature and cell viability of biocompatible nano Yttria stabilised zirconia coated on 316L SS for dental applications

Development of biocompatible dental implants has become significant impact in dental industry. In the present work, we report for the development of biocompatible nano Yttria stabilised Zirconia (YSZ) coatings on 316L stainless steel (316L SS) obtained by EPD process. The optimized sample (nano YSZ coating on 316 obtained at applied potential of 70 V for 5 minutes) were sintered in air at 600, 800 and 900°C. The surface morphology and composition of the coatings were characterized by XRD and FE-SEM with EDAX. The electrochemical performance of the uncoated metal and nano YSZ coated 316L SS samples were evaluated in artificial saliva (AS) medium using electrochemical techniques such as Open Circuit Potential – time measurement (OCP), Electrochemical Impedance Spectroscopy (EIS) and Cyclic Potentiodynamic Polarization (CPP).

Composition Optimization, High-temperature Stability and Thermal Cycling Performance of Sc-doped Gd2Zr2O7 Thermal Barrier Coatings: Theoretical and Experimental Studies

Sc was doped into Gd2Zr2O7 for expanding the potential for thermal barrier coating (TBC) applications. According to first-principles calculation, solid solution mechanism of Sc in Gd2Zr2O7 lattice was revealed, i.e., Sc atoms first occupy the lattice interstitial sites followed by substituting for Gd, and the interstitial Sc concentration is less than 11.11 at. %. By considering the mechanical and thermophysical properties comprehensively, the optimum Sc doping content was determined to be 16.67 at. %, and this Sc content was selected to produce TBCs by air plasma spraying with YSZ as a bottom ceramic coating (Gd-Sc/YSZ TBC). After sintering at 1400 ℃ for 100 h, Gd-Sc coatings retain phase and structural stability indicative of excellent sintering resistance. By thermal cycling tests, Gd-Sc TBCs fail due to the low toughness and the interface reaction between Gd-Sc and bond coat, while Gd-Sc/YSZ TBCs exhibit much longer thermal cycling lifetime, and the failure mode is YSZ coating cracking.

Comparative Studies of Piston Crown Coating with YSZ and Al2O3·SiO2 on Engine out Responses Using Conventional Diesel and Palm Oil Biodiesel

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.

Composition Optimization, High-temperature Stability and Thermal Cycling Performance of Sc-doped Gd2Zr2O7 Thermal Barrier Coatings: Theoretical and Experimental Studies

Sc was doped into Gd2Zr2O7 for expanding the potential for thermal barrier coating (TBC) applications. According to first-principles calculation, the solid solution mechanism of Sc in Gd2Zr2O7 lattice was revealed, i.e., Sc first occupies the lattice interstitial sites followed by substituting for Gd, and the interstitial Sc concentration is less than 11.11%. By considering the mechanical and thermophysical properties comprehensively, the optimum Sc doping content was determined to be 16.67%, and this composition was selected to produce TBCs by air plasma spraying with YSZ as a bottom ceramic coating (Gd-Sc/YSZ TBC). After sintering at 1400 ℃ for 100 h, Gd-Sc coatings remain phase and structural stability indicative of excellent sintering resistance. By thermal cycling tests, Gd-Sc TBCs fails due to the low toughness and the interface reaction between Gd-Sc and boding coatings, while Gd-Sc/YSZ TBCs exhibit much longer thermal cycling lifetime, and the failure mode is YSZ coating cracking.

Residual Stresses in Suspension Plasma Sprayed Electrolytes in Metal-Supported solid Oxide Fuel Cell

This study is aimed at identifying the change of residual stresses in suspension plasma sprayed (SPS) 8 mol% YSZ electrolytes on top of porous stainless steel substrate with varying processing parameters and temperatures. The residual stresses in the electrolyte layer are tensile with a value of approximately 90 MPa at room temperature. Porosity, microcracks and segmentation cracks are observed to form in the coating during post-deposition cooling. The decrease of residual stresses with increasing temperature is related to the changes in the Young’s modulus, thermal expansion mismatch, micro-defects and possible creeping of porous stainless steel substrate. The coating fabricated using a torch power of 133 kW and stand-off distance of 90 mm exhibits the highest residual stress due to the formation of a denser microstructure and less cracking. Furthermore, the fracture toughness and interface fracture toughness of the SPS YSZ coating at the optimized condition was determined and discussed.

Residual Stresses in Suspension Plasma Sprayed Electrolytes in Metal-Supported solid Oxide Fuel Cell

This study is aimed at identifying the change of residual stresses in suspension plasma sprayed (SPS) 8 mol% YSZ electrolytes on top of porous stainless steel substrate with varying processing parameters and temperatures. The residual stresses in the electrolyte layer are tensile with a value of approximately 90 MPa at room temperature. Porosity, microcracks and segmentation cracks are observed to form in the coating during post-deposition cooling. The decrease of residual stresses with increasing temperature is related to the changes in the Young’s modulus, thermal expansion mismatch, micro-defects and possible creeping of porous stainless steel substrate. The coating fabricated using a torch power of 133 kW and stand-off distance of 90 mm exhibits the highest residual stress due to the formation of a denser microstructure and less cracking. Furthermore, the fracture toughness and interface fracture toughness of the SPS YSZ coating at the optimized condition was determined and discussed.