Atmospheric plasma spraying is attractive for manufacturing solid oxide fuel cells (SOFCs) because it allows functional layers to be built rapidly with controlled microstructures. The technique allows SOFCs that operate at low temperatures (500 to 700 °C) to be fabricated by spraying directly onto metallic supports. However, standard cathode materials used in SOFCs have high polarization resistance at low temperatures, necessitating alternative materials. In this study, coatings of lanthanum strontium cobalt ferrite (LSCF) were fabricated on steel substrates using axial-injection atmospheric plasma spraying. Coating thickness and microstructure were evaluated and X-ray diffraction (XRD) analysis was performed to detect material decomposition and the formation of undesired phases in the plasma. The results define the envelope of plasma spray parameters for depositing LSCF coatings and the conditions in which composite cathode coatings can be produced.

A fundamental study of inelastic deformation of freestanding plasma-sprayed thermal barrier coatings (TBCs) has been conducted. Cantilever-type bending tests are carried out to obtain stress-strain curves from freestanding ceramic layers detached from the TBC-coated sample via electrochemical treatment. In order to investigate inelastic deformation in the sample, in-situ scanning electron microscope (SEM) observation is performed by means of a small tensile testing device that can be inserted into the SEM vacuum chamber. The bending test result indicated that the coating deforms with a nonlinear behavior under monotonic loading, in spite of the fact that it is a ceramic material. Spray parameters such as in-flight velocity affected the stress-strain curve significantly. In-situ SEM observation during the bending test revealed that sliding at boundaries between splats plays an important role in inelastic deformation.

Plasma-sprayed yttria-stabilized zirconia (YSZ) can be potentially employed as electrolyte coating in solid oxide fuel cells (SOFCs). The formation of a convex coating surface with semi-melted particles will increase the specific surface area and subsequently improve the output performance of SOFCs. However, using completely molten YSZ particles during plasma spraying leads to the formation of locally flat surface owing to the spreading of the liquid droplets on impact. In this study, flame spraying was employed to deposit YSZ particles on YSZ substrate using surface-melted particles. 4.5 mol% YSZ powder particles were used as spray materials. The deposition was carried out at different spray distances on the YSZ substrate preheated to 650 °C. The surface morphology of YSZ particles was characterized by SEM. The bonding of YSZ particles with the underlying YSZ substrate was examined from cross section. The electrochemical behavior of a single cell with a structured cathode was analyzed by electrochemical impedance spectroscopy. The results show that spray distance has significant influence on the morphology of deposited YSZ particles. The cathode polarization of a structured cathode was decreased by about 30% compared to a flat cathode.

This paper presents a method, based on push-rod type thermomechanical analysis, for determining the thermal expansion behavior of thermal barrier coatings (TBCs). It shows that TMA measurements can provide accurate CTEs for yttria-stabilized zirconia layers as thin as 0.3 mm with good reproducibility and low measurement error (< 5%). The method was also used to assess the effect of annealing on thermal expansion behavior, revealing a slightly monotonic decrease in the CTE of YSZ samples.

Thermal barrier coatings (TBCs) consisting of a yttria-partially-stabilized zirconia (YSZ) topcoat and a metallic bond coat are used to protect components in high temperature environments such as the hot section of a gas turbine. In this study, the bond coats have been fabricated using different thermal spray processes, including vacuum arc spaying, high-velocity oxyfuel flame spraying, low-pressure plasma spraying, air plasma spraying, and detonation spraying. The microstructure of the resulting TBCs is characterized based on XRD, SEM, and TEM analysis and various properties are measured, including high-temperature oxidation, cohesion strength, thermal impact, and heat insulation temperature.

In this study, agglomerated nanocrystalline ZrO 2 --Y 2 O 3 powder was calcinated from 900 to 1300 °C for 2 h. The calcinated nanopowder was used as feedstock and deposited by air plasma spraying on a NiCoCr bond coat applied to a nickel substrate via low pressure plasma spraying. For comparison, conventional ZrO 2 -Y 2 O 3 topcoats were also produced. Nanostructured and conventional thermal barrier coatings were calcinated from 1050 to 1250 °C for 2-20 h. Experimental results indicate that monoclinic tetragonal phases in the agglomerated nanopowder were transformed into cubic phase after calcination. The cubic phase content increased with increasing calcination temperature. High temperature calcination can make the yttria segregated at grain boundaries dissolve in zirconia. Different from the phase constituent of the as-sprayed conventional TBC, which consisted of diffusionless transformed tetragonal, the as-sprayed nanostructured TBC consisted of cubic phase containing high yttria. No phase transformations were observed in either TBC after calcination.

This study investigates the influence of segmentation crack density on the strain tolerance of thermal barrier coatings produced by atmospheric plasma spraying. A Triplex II plasma gun is used to spray fused and crushed yttria-stabilized zirconia, forming thick deposits with high segmentation crack densities, low porosity, and low branching crack density, which is necessary for good interlamellar bonding. Thermal cycling and burner rig tests yield promising results in terms of lifetime and strain tolerance behavior and microstructural analysis shows that the segmentation crack network was stable during thermal shock testing. The main failure mechanism was delamination and horizontal cracking in the vicinity of the TBC-TGO (thermally grown oxide) interface.

The aim of this work is to measure the optical reflective properties of plasma sprayed ceramic coatings on glass substrates. The coatings are made with Al 2 O 3 -TiO 2 powders and are assessed by scanning them with an optical computer mouse. It is shown that mouse movements are smoother on ceramic surfaces than on a standard test pad and tracking performance is more stable, indicating that the reflective properties of ceramic-coated glass are better than those of a typical mouse pad. The ceramic coatings are also shown to have the potential to improve resolution in image recording devices.

In this work, digital image processing and finite element analysis are used to predict physical properties of thermal barrier coatings based on microstructure. Factors that affect thermal conductivity such as porosity, crack morphology, and interface defects are systematically studied. It is shown that transverse cracks can significantly retard the transfer of thermal flux and that the effective TCE and elastic modulus at the coating interface is determined mainly by composition, with interface morphology having little effect. Furthermore, no anisotropy was found at the interface. Unlike traditional property-prediction methods, the methodology presented in this paper reflects real coating microstructures, thus providing more accurate results.

Thermal conductivity of plasma-sprayed YSZ thermal barrier coatings depends on microstructure and significantly influences the effectiveness of the thermal barrier. In this study, YSZ coatings are deposited by plasma spraying using fused and crushed Y 2 O 3 -ZrO 2 powder. Coating microstructure was modified by substrate temperature, which was varied from room temperature to 880 °C during deposition. The coating microstructure was examined from the fractured cross-section of the deposits to reveal changes in interlamellar bonding due to substrate temperature. The thermal conductivities of the YSZ coating were tested by laser flashing from room temperature to 1300 °C. The results showed that the coating deposited at room temperature exhibited a typical lamellar structure and a thermal conductivity of 1.26 W·m -1 ·K -1 measured at room temperature. With the increase of substrate temperature, the thermal conductivity was increased. The coating deposited at a substrate temperature of 840-880 °C consisted of trans-lamellae long columnar grains and exhibited a value of 1.95 W·m -1 ·K -1 at room temperature. The influence of substrate temperature on thermal conductivity is discussed based on the changes in microstructure observed.

In this study, La 10 (SiO 4 ) 6 O 3 coatings deposited on aluminum substrates by atmospheric plasma spraying were investigated for potential for use as electrolyte layers in solid oxide fuel cells. By proper selection of spraying parameters, particularly the hydrogen gas flow rate, the La 10 (SiO 4 ) 6 O 3 ceramic layers showed good densification. The results suggest that atmospheric plasma spraying may be an appropriate method for the production of SOFCs.

In this study, molecular dynamic simulations are used to analyze the effect of dopant concentration on the performance and stability of zirconia-based solid electrolyte. Different amounts of Sc 2 O 3 are diffused into the YSZ system to simulate various Sc-Y-SZ electrolyte compositions for analysis. The calculations predict that ionic transport efficiency improves with increasing Sc 2 O 3 concentration as does the mobility of oxygen ions. The simulated results agree well with experimental data, indicating that the molecular dynamic technique may be helpful in the design and development of materials for SOFC applications.

In this investigation, two complex perovskite powders, Ba(MgTa)O and Ta(AlMgT)O, are deposited by atmospheric plasma spraying and evaluated for use as thermal barrier layers. Process parameters are optimized to provide sufficient melting without causing the formation of secondary phases. Deposited coatings are assessed based on composition, morphology, porosity, and thermal cycling lifetime. It is shown that the nature of the starting powders has a significant effect on the lifetime and performance of perovskite-based thermal barrier coatings.

This study investigates the influence of thermally grown oxide (TGO) on the lifetime of thermal barrier coatings (TBCs). In the experiments, cold sprayed NiCoCrAlY powder was deposited as the bond coat and plasma sprayed YSZ was deposited as the topcoat. The TBCs were subjected to various treatments to induce different types of TGOs at the bond coat-topcoat interface. Three types of oxide were detected, including spinel, chromium oxide, and alumina. Thermal cycling tests show how the oxides contribute to cracking and spalling in the topcoat layer and how the morphologies and constituents of the oxides can change with time and temperature.

This work investigates the effect of calcium-magnesium aluminosilicate (CMAS) deposits on thermal barrier coatings. CMAS infiltration was achieved by means of a cement tape containing synthetic glass powder. The tape was placed on coating surfaces and melted in a tube furnace or with a flame burner. The resulting coating failures were investigated by examining thermomechanical and thermochemical interactions between the coatings and aluminosilicate deposits. It was found that the porous nature of thermal spray TBCs makes them vulnerable to CMAS attack even before discernible chemical reactions start. Possible mitigation approaches are proposed for improving coating life under such conditions.

Mullite based compositions have interest for thermal barrier coatings because they have thermal expansion coefficients close to those of silicon ceramic substrates. In this work, mullite-zirconia coatings are obtained by flame spraying and characterized based on microstructure, crystal phases, hardness, elastic modulus, and thermal conductivity. Crystallinity is improved by in-situ heating with a flame torch, which is also shown to increase hardness and elastic modulus. Thermal diffusivity measurements show that the thermal properties of mullite-zirconia coatings are relatively stable over a wide temperature range and adequate for many thermal barrier applications.

This study investigates the degradation of YSZ-CoNiCrAlY thermal barrier coatings (TBCs) due to vanadium and phosphorus pentoxides and calcium-magnesium aluminosilicate (CMAS) sand at temperatures up to 1400 °C. The pentoxides are shown to degrade bond coat and topcoat layers through acidic dissolution, while CMAS sand is shown to degrade YSZ layers through ingress and the precipitation of ZrO 2 grains. Density functional theory simulations provide insights on reactions at the surface of fluorite-structured oxides and the role of oxygen vacancy clustering. A method to mitigate melt-infiltration attack through electrophoretic deposition is introduced.

This study investigates the influence of powder morphology and spray processes on the microstructure, crystallinity, hardness, and elastic modulus of mullite coatings. Coatings produced from mullite powders and suspensions are deposited by plasma spraying while measuring in-flight particle temperature and velocity. Powder morphology and spraying conditions are correlated with measured coating properties, creating a process map for engineering mullite coatings for specific applications. It is shown that coating crystallinity, microstructure, and mechanical properties vary widely depending on powder morphology, processing, and in-flight particle characteristics.

In this study, the deposition, microstructure, and resistivity of APS and HVOF sprayed Cr 2 O 3 -TiO 2 coatings is systematically investigated. Commercially available Cr 2 O 3 -rich feedstock powders are used along with five agglomerated and sintered experimental powders on the TiO 2 -rich side. Both processes are found to produce homogeneous, low-porosity coatings with phase compositions that can be changed by adjusting process parameters. Coating hardness and electrical resistivity are found to depend heavily on Cr 2 O 3 content.

This study investigates the feasibility of manufacturing lanthanum silicate coatings for solid oxide fuel cells by atmospheric plasma spraying. The coatings produced are cohesive, relatively dense, and contain no secondary phases. Test results show that the starting composition of the powder is maintained after spraying and that particle velocity depends primarily on the plasma gas mixture. Due to the relatively high melting temperature of the particles, dense apatite coatings with few microstructural defects are obtained.