Thermal Barrier Coatings Material Research Articles

Research progress of rare earth doped thermal barrier coatings

Thermal barrier coating (TBC) is a kind of thermal insulation and protective ceramic material, which can effectively improve the working temperature and service life of aero-engine. It has important economic value and strategic position in this field. With the further improvement of thrust-to-weight ratio, the traditional YSZ coating no longer can meet the technical requirements of the new generation engine. In recent years, scholars both at home and abroad have shown that rare earth doping can improve the performance of TBCs to a certain extent. Therefore, rare earth doping modification has become the focus of the development of new high-performance TBCs. In this paper, the applications of rare earth doping in high-performance TBCs are summarized, with emphasis on the effects of rare earth doping on the mechanical, thermal-physical and corrosion resistance of TBCs to molten CMAS. The problem of performance deterioration of TBCs when rare earth is over doped and the deficiency in rare earth selection standard is discussed. Moreover, it is considered that the selection basis of rare earth doping amount and type will be the research focus of TBC materials in the next generation. How to further improves the performance of TBCs is the future development direction of rare earth doped TBCs.

Spontaneously formed nanostructures in double perovskite rare-earth tantalates for thermal barrier coatings

The identification of low thermal-conductivity materials that are stable up to high temperatures has been a longstanding challenge for high-temperature thermal management systems such as thermal barrier coatings (TBCs). Although phonon scattering in crystalline solids can be enhanced by nanometer-scale boundaries as well as well-studied atomic-level point defects, the impact of such extended defects on heat transfer in high-temperature applications remains unclear. Herein, through structural characterization and measurements of the thermophysical properties of rare-earth tantalates with double-perovskite structures (RTa3O9; R = La, Nd, Gd, and Yb), it is shown that YbTa3O9 with spontaneously formed nanostructures has a thermal conductivity lower than two-thirds of that of the commercial-level TBC material, i.e., 7 wt% yttria-stabilized zirconia (7YSZ). These results provide evidence of the close relation between enhanced phonon scattering and boundaries separated by distances of few nanometers which contain periodic strain, octahedral tilting, and twin-boundaries. Furthermore, YbTa3O9 exhibits similar thermal expansion characteristics to 7YSZ without any apparent transition associated with a disrupt change in volume, which suggests its potential as a TBC material. The results demonstrate the capability of tuning closely aligned boundaries in crystals to control thermal transport and tailor low-thermal conductivity materials.

Interfacial Structure and Physical Properties of High-Entropy Oxide Coatings Prepared via Atmospheric Plasma Spraying

The feasibility of using a high-entropy rare-earth oxide (REO) as a top coating material for thermal barrier coatings was explored using the atmospheric plasma spray technique. The microstructure and Vickers hardness of the coating layer were compared to those of an 8 mol % yttria-stabilized zirconia (8YSZ) top coating material. Macroscopic observations revealed the formation of a well-coated surface with no surface defects or delamination. Scanning electron microscopy images showed the presence of several parallel and vertical microcracks in the REO and 8YSZ coating layers. The origin of these cracks is attributed to differences in the coefficient of thermal expansion, very fast cooling, and process parameters. X-ray diffraction demonstrated the high phase stability and excellent thermal properties of REO due to the absence of phase transformation after plasma spray processing. The measured Vickers hardness of REO was 425 HV, which is lower than that of sintered REO powder and the 8YSZ coating.

A new class of high-entropy fluorite oxides with tunable expansion coefficients, low thermal conductivity and exceptional sintering resistance

High-temperature thermal barrier coating (TBC) materials are desired for the development of high-efficient gas turbines and diesel engines. Herein, to meet up with this requirement, a new class of high-entropy fluorite-type oxides (HEFOs) has been synthesized via a solid-state reaction method. Comparing to La2Ce2O7, a promising TBC material, the HEFOs exhibit similar high thermal expansion coefficients (TECs) of 11.92×10−6∼12.11×10−6 K-1 at temperatures above 673 K but a better TEC matching performance at the temperature range of 473–673 K. It is also found that through tuning the average A-site cation radius, the TEC of the HEFOs could be tailored efficiently. The HEFOs also possess low thermal conductivities of 1.52-1.55 W∙m-1∙K-1 at room temperature, which is much lower than that of La2Ce2O7 and comparable to pyrochlores as Gd2Zr2O7. Moreover, the HEFOs display good sintering resistance and phase stability even at temperatures as high as 1873 K. The combination of these fascinating properties makes the HEFOs good candidates for thermal barrier coating and thermal insulating materials.

New class of high-entropy defect fluorite oxides RE2(Ce0.2Zr0.2Hf0.2Sn0.2Ti0.2)2O7 (RE = Y, Ho, Er, or Yb) as promising thermal barrier coatings

High-entropy ceramics exhibit great application potential as thermal barrier coating (TBC) materials. Herein, a series of novel high-entropy ceramics with RE2(Ce0.2Zr0.2Hf0.2Sn0.2Ti0.2)2O7 (RE2HE2O7, RE = Y, Ho, Er, or Yb) compositions were fabricated via a solid-state reaction. X-ray diffraction (XRD) and energy dispersive spectrometry (EDS) mapping analyses confirmed that RE2HE2O7 formed a single defect fluorite structure with uniform elemental distribution. The thermophysical properties of the RE2HE2O7 ceramics were investigated systematically. The results show that RE2HE2O7 ceramics have excellent high-temperature phase stability, high thermal expansion coefficients (10.3–11.7 × 10−6 K-1, 1200 ℃), and low thermal conductivities (1.10-1.37 W m-1 K-1, 25 ℃). In addition, RE2HE2O7 ceramics have a high Vickers hardness (13.7–15.0 GPa) and relatively low fracture toughness (1.14-1.27 MPa m0.5). The outstanding properties of the RE2HE2O7 ceramics indicate that they could be candidates for the next generation of TBC materials.

YAG thermal barrier coatings deposited by suspension and solution precursor thermal spray

Yttrium aluminium garnet (YAG) is a promising topcoat material for thermal barrier coatings due to its high temperature stability and better CMAS (calcium-magnesium-alumino-silicate) resistance. YAG topcoats were deposited by suspension and solution precursor high-velocity oxy-fuel (HVOF) thermal spray. The relationships between processing, microstructure and final properties were studied through a range of characterization techniques and thermal cycling tests. The microstructure of the as-sprayed YAG topcoat from stoichiometric solution precursor (SP-YAG) had distributed pores and inter-splat boundaries, while the as-sprayed topcoat produced from suspension (S-YAG) had vertical and branched micro cracks, pores, and inter-splat boundaries. Both as-sprayed coatings were composed of amorphous phase, hexagonal yttrium aluminium perovskite (YAP) and cubic YAG. In thermal cycling tests, 20% of SP-YAG failure was reached after the 10th cycle; whereas, S-YAG reached the failure criteria between the 60th and 70th cycle. The failure of both the SP-YAG and the S-YAG topcoats occurred due to thermal stresses during the thermal cycling.

Low-calcination temperatures of magnesia partially stabilized zirconia (Mg-PSZ) nanoparticles derived from local zirconium silicates

Partially stabilized zirconia (PSZ) exhibits excellent physical, mechanical, electrical, chemical, thermal, and bioactive properties. Therefore, it is frequently used as a material for thermal barrier coatings, refractories, oxygen-permeating membranes, dental and bone implants. In this study, magnesia-partially stabilized zirconia nanoparticles were successfully prepared from zirconium silicates and MgSO4 assisted with PEG-6000 via a facile templating method. The MgO concentration was varied from 1%–10% in wt% of ZrO2. Zirconium silicates were initially converted to Zr-precursor solution, exhibiting pH 3. Then, the appropriate amount of the Mg-precursor was mixed with the proper amount of the Zr-precursor solution. A 10%(w/v) PEG-6000 solution was added into the PSZ precursor solution at a ratio of the precursor-to-PEG volumes of about 15:1 under stirring and heating, resulting in a very fine white gel. The gel was filtered, dried, and then calcined at elevated temperatures of 600, 800, and 1000 °C. The characteristics of the final product were then evaluated. According to the experimental results, the MgO concentration influences the ZrO2 phase transformation at elevated calcination temperatures. In this study, the lower the MgO dopant concentration added into ZrO2, the more stable the t- ZrO2 phase in PSZ samples at high temperatures. However, the MgO presence is detected as periclase in all samples with a very low peak intensity at elevated calcination temperatures. The obtained PSZ samples consist of nanoparticles and high agglomeration, some of particles exhibit elongated and rod-like shapes. The PEG existence during the PSZ preparation has restrained particle interaction and aggregation of the as-synthesized PSZ samples, leading to PSZ nanoparticles evolution.

Rheological and chemical interaction between volcanic ash and thermal barrier coatings

Combustion temperatures (>1200 °C) in gas turbines cause softening and eventually melting of ingested volcanic ash particles. In the downstream section, lower temperatures lead to droplet deposition onto the thermal barrier coatings (TBCs) of the turbine blades. The intensity of interaction (wetting and chemical interaction) depends on the ash and TBC chemistry as well as the TBC structure. We have determined the spreading behavior of five different volcanic ash melts on four types of TBCs. The TBCs differed in their composition - yttria-stabilized zirconia (YSZ) and gadolinium zirconate (GZO) – and in their fabrication - air plasma spraying (APS) and electron-beam physical vapor deposition (EB-PVD). The spreading properties have been parameterized on the basis of four parameters, 1) the CaO-SiO 2 -ratio, 2) optical basicity, 3) the R b/a ratio and 4) the viscosity of the volcanic ash melts. Infiltration efficiency of the melts into the TBCs and corrosion characteristics have been determined via electron microprobe analysis of cross sections. In this study, the highest damage potential was found following interaction with basaltic melt, as its low viscosity is favorable to extensive spreading and high chemical reactivity. • Basaltic (SiO 2 -lean) silicate melts show the most extensive spreading on TBC surfaces and the most intense chemical reaction with the TBC materials • Spreading of silicate melts on APS TBCs is enhanced over EB-PVD TBCs and spreading on GZO TBCs is enhanced over YSZ TBCs • Spreading ability of silicate melts can be estimated based on a parametrization deduced from our spreading experiments

Multifarious Defects Co-Determined Thermal Conductivity in Air Plasma Sprayed Thermal Barrier Coatings

Yttria-stabilized zirconia (YSZ) is the most widely applied thermal barrier coatings (TBCs) materials in gas turbines and aviation engines to prevent components from overheating and to increase the combustion temperature and turbine efficiency. Plasma sprayed coatings usually contain about 15~25% pores, mainly including globular pores, cracks and amorphous phase that to be classified as multifarious and multi-scale defects. They all significantly lower the thermal conductivity, but in drastically different ways depending on their morphologies and orientations. Establishing an accurate correlation between the total porosity and the thermal conductivity requires not only a precise separation and estimation of different kinds of defects but also a reasonable mathematic model to describe their effect on the thermal conductivity. In the present research, cross-section ion polishing and image analysis were chosen as a reliable assembly for visualizing and characterizing multifarious defects of thermal sprayed coatings, through which tiny pores and cracks can be distinctly expressed without any mechanical damage of the microstructure. The effect of different micro-scale defects such as pores and cracks on the thermal conductivity was respectively and quantitatively calculated according to a Bruggeman-based iterative model. Additionally, the nanoscale defects, especially the amorphous phase in the matrix was also taken into consideration, which is proven to be of great importance. The predicted thermal conductivity based on this amorphous-phase-concerned iterative model has achieved a successful evaluation compared to the measured results of coating specimens originated from various spraying processes. This research confirms the applicability of image-analysis-based modeling as a simple, reliable and versatile method for thermal conductivity prediction of porous coating systems.

Plasma sprayed 18mol% YO1.5 stabilized hafnia as potential thermal barrier coating

Considerable efforts are being invested to explore alternative ceramic materials to yttria stabilized zirconia (YSZ) for thermal barrier coating (TBC) applications. In this work, 18 mol% YO1.5 stabilized HfO2 (18YSH) is proposed as potential TBC material. Stoichiometric 18YSH was prepared by atmospheric plasma spraying. The 18YSH coating exhibits low thermal conductivity over the whole temperature range investigated and a minimum thermal conductivity of 0.832 W/m·K at 800 °C. Average hardness and Young's modulus values have been determined to be 7.01 ± 1.33 GPa and 111 ± 26.8 GPa respectively. These values are superior to those exhibited by YSZ coating. In addition, the sintering temperature of 18YSH coating is at least 100 °C higher than that of a 8 YSZ coating and thus 18YSH will be more resistant to sintering. Finally, 1) the coating reliability of 18YSH TBC has been studied by thermal cycling to 1100 °C and 2) calcium–magnesium–alumino-silicate-(CMAS)-induced degradation was investigated at 1250/1300 °C. The related failure mechanism was investigated and a model describing the CMAS degradation process is presented.

Influence of SiC Addition on Mechanical Behavior of Thermal Barriers with the Aid of Acoustic Emission

The improvement of high temperature materials with lower heat transfer coefficients lead to the development of thermal barrier coatings (TBCs). One of the most widely used materials for thermal barrier coatings is Y2O3 stabilized ZrO2 (Y-TZP) because of its excellent shock resistance, low thermal conductivity, and relatively high coefficient of thermal expansion. The aim of this work is to study the TBCs mechanical behavior with the addition of SiC into the suspension of Y-TZP/Al2O3 by acoustic emission (AE). Additionally, a microstructural analysis and a finite elements model were carried out in order to compare results. The coatings were made by suspension plasma spray (SPS) on metal plates of 70 × 12 × 2 mm3. An intermetallic was deposited as a bond coating, followed by a coating of Y-TZP/Al2O3 with and without 15 wt.% SiC, with thicknesses between 87 and 161 μm. The AE becomes a fundamental tool in the study of the mechanical behavior of thermal barriers. The use of wavelet transforms streamlines the study and analysis of recorded sound spectra. The crack generation arises at very low stress levels.

Ceramic Material for Thermal Barrier Coatings in Compression Ignition Engine for its Performance Evaluation with Biodiesel

In the present investigation, a Dongfeng compression ignition (CI) engine powered by biodiesel and diesel fuel, and analysed to gauge performance when coupled with a Thermal Barrier Coating (TBC) coated combustion chamber. TBC in CI engine improves its thermal retention and enhances biodiesel usability, which has a higher flashpoint than diesel. Biodiesel extracted from non-edible Pongamia Pinnata seeds is blended with diesel in various ratios to prepare 20BD (20%Pongamia Biodiesel + 80%diesel), 50BD and 100BD blends for the experiment. The properties of these fuel blends were tested by following American Standard for Testing and Materials (ASTM) approved testing methods to check their suitability as fuel for the CI engine. The piston crown, cylinder liner, inlet, and exhaust valves surface coated with TBC. The TBC is composed of a bond coat applied on the substrate which needs to be thermally insulated and a topcoat of ceramic material over bond coat. The bond coat of NiCrAl (Nickel-Chromium-Aluminium) of thickness 1 mm and a 4 mm topcoat of Titanium dioxide (TiO2) coated using the plasma spray coating method. A comparative study between a coated and uncoated engine component with diesel and biodiesel blends to study performance effects. The results show that the CI engine with 20BD, consumed 10.6% lower fuel when used in a coated engine than in an uncoated engine. Brake thermal and mechanical efficiency with 20BD were increased by 4.7%, and 2.6% respectively in TBC sprayed CI engine at part load. The lower the heat loss to coolant from the engine, the lower the consumption of fuel. An increase in heat retention in the coated combustion chamber leads to a boost in fuel vaporisation and a shortening of physical ignition delay. Hence, the CI engine's modification to accommodate biodiesel with TBC has a net positive impact on fuel consumption and engine efficiency.

Processing, characterisation and oxidation resistance of βNiAl bond coat: Al and Zr effects

Platinum-modified-?NiAl is a bond coat (BC) material for thermal barrier coatings (TBCs) applications applied on aeroengine hardware to reduce their surface temperatures. However, it is desirable to minimize its production and material costs by the low-cost alternatives of similar performance. It has been acknowledged that the small concentration of the reactive elements (REs), such as Zr, Hf, and Y, could tremendously enhance the oxide adhesion even in some cases better than Pt modified counterparts. The aim of this study was to design and fabricate the Zr-modified-?NiAl bond coat on CMSX-4 superalloy using an aluminizing method. Moreover, the study focused on the development of a systematic understanding of underlying mechanisms behind the beneficial effects of REs. Initially, three sets of BCs were prepared: Zr-free ?NiAl (undoped), Al and Zr co-deposited in a single-step process (1SP), and Zr and Al, which were individually deposited in two processing steps (2SP): zirconizing and aluminizing. Such three sets of BCs helped to understand the processing, as well as Zr and Al effects on scale adhesion. In particular, 1SP/2SP BCs showed uniformity of Zr in the form of precipitates and networks that caused hardness enhancement. All BCs were isothermally oxidized at 1150?C for 100 hours wherein 2SP revealed the best spallation resistance, microstructural stability, and its Zr-oxide pegs were extended to substrates. In addition to the Zr effect, BC Al content was found to affect the oxide adhesion equally. Under identical Zr contents (of 1SP and 2SP = 1at %), the higher Al showed the better spallation resistance while lower Al caused the inverse effect of Zr owing to its reactive nature that was termed as over doping. Moreover, it was established that over-doping either local or into entire BC, accelerated the Al depletion that destabilized the ?NiAl into ??-Ni3Al phase. An extensive discussion is presented in the light of the observed results.

Study on thermal, mechanical, microstructural properties and failure analyses of lanthanum zirconate based thermal barrier coatings: A review

This research study summarizes the recent information about the characteristics of multi layer and composite lanthanum zirconate based thermal barrier coatings (TBCs) that provide high-temperature thermal protection for the jet engines parts. Thus the outcome of lightweight gas turbine components able to work at 3000° F nearly 1650 °C needs to be built. Such difficulties can be solved using coatings with optimized microstructure and chemical composition. Recently, Lanthanum zirconate (La2Zr2O7-LZ) based pyrochlore oxides (Ra2Zr2O7, Re = rare earth) are now developing TBC material, owing to their fewer thermal conductivity with enhanced stability at elevated operating temperatures. Even though LZ cannot be directly replaced for standard YSZ because of its mismatch between the grew of thermal oxide (TGO) film. When LZ compared to Zirconia partially stabilized with yttria (YSZ), LZ possesses a poor thermal conductivity, lesser coefficient of thermal expansion, lower sintering ability, and lack of toughness than YSZ. Hence LZ comes to be combined with standard TBC YSZ in order to integrate advantages in multilayer architecture. In this study describes the thermal, mechanical and physical properties and failure analysis of Multilayer LZ/YSZ were described. It also reviews the characterization of coatings according to different criteria and conditions. At last, suggestions for investigation on layered LZ based TBCs applications for next-generation was indicated.

Numerical investigation of the effect of thermal barrier coating on combustion and emissions in a diesel engine

Thermal barrier coating (TBC) has been used as an effective way to reduce the heat transfer losses and to improve the thermal efficiency of internal combustion (IC) engine. However, the NOx and other emissions will be affected after the addition of coating in engine cylinder. Therefore, it is necessary to investigate the relation between TBC on improving engine performance and its negative effects. In this work, TBC model has been improved and applied to investigate the effects of TBC properties on engine combustion and emissions at low loads. TBC material parameters, including thermal conductivity, specific heat capacity and porosity, have been studied within reasonable ranges. It is found that with the increase of porosity and reduction of thermal conductivity, the in-cylinder gas temperature can be increased up to about 100–200 K. Meanwhile, the exhaust temperature also increases, thus the conversion efficiencies of diesel oxidation catalyst (DOC) and selective catalytic reduction (SCR) can be increased and much lower emissions can be obtained. However, the specific heat capacity (cp) only affects the peak of heat release rate and the thermal efficiency only has small fluctuation with the increase of cp. This research has the guiding significance and practical value for the selection of coating materials and the improvement of coating spraying method. In the future, the durability of coating materials is a potential research direction.

The influence of thermal barrier coating dissolution on CMAS melt viscosities

Glassy deposits, largely consisting of CaO-MgO-Al2O3-SiO2 (CMAS), are a common product on thermal barrier coatings (TBCs) within gas-turbines after an interaction with airborne particles. Here, in order to facilitate the quantification and modelling of the spreading and infiltration behavior of CMAS melts onto and into TBCs we have determined the high temperature viscosities of four widely used synthetic “CMAS” melts and the influence of TBC materials (yttria-stabilized zirconia (YSZ) and gadolinium zirconate (GZO)) dissolution upon them. After a dissolution of 6.5 wt% YSZ or GZO one out of four CMAS melts shows no significant change in viscosity, while the other three melts exhibit a viscosity increase at lower temperatures that continuously changes to a decrease in viscosity towards higher temperatures. The influence of the doping amount on the viscosity was investigated in detail for one CMAS melt (C35M10A7S48) and parametrized.

Outstanding sintering resistance in pyrochlore-type La2(Zr0.7Ce0.3)2O7 for thermal barrier coatings material

Sintering of advanced thermal barrier coatings (TBCs) at high temperatures is key challenge as it can adversely affect service performance and thermal fatigue resistance of TBCs. In this study, sintering behavior of pyrochlore-type La2(Zr0.7Ce0.3)2O7 (LZ7C3) was investigated using experiments and molecular dynamics. Meanwhile, the corresponding dynamic process and behind mechanism were uncovered. Results showed that novel LZ7C3 exhibited significantly higher sintering resistance than host La2Zr2O7 (LZ) and typical 8 wt% yttria-stabilized zirconia (8YSZ) at temperature up to 1773 K, which indicated that pyrochlore-type LZ7C3 is a promising TBC candidate to replace conventional 8YSZ at high temperatures. Further study also revealed that initial stage played crucial role in sintering process, and the sintering mainly occurred at grain boundary (GB) region. Intrinsic sintering activation energy of LZ7C3 GB (695.248 J mol−1) is larger than that of LZ GB (384.171 J mol−1) and 8YSZ GB (173.303 J mol−1), which resulted in outstanding sintering resistance for LZ7C3. Furthermore, no obvious enrichment of second phase was observed at the GB of LZ7C3. This study thus concluded that hindering the atomic diffusion of GB, as well as introducing foreign atom with larger mass and bond energy may act as effective strategy to enhance the sintering resistance of TBCs materials.

Equimolar YO1.5 and TaO2.5 co‐doped ZrO2 as a potential CMAS‐resistant material for thermal barrier coatings

AbstractCalcium‐magnesium‐alumino‐silicates (CMAS) corrosion in thermal barrier coatings (TBCs) is becoming more serious with increasing operation temperature of turbine engines. Here, we report an equimolar YO1.5 and TaO2.5 co‐doped ZrO2 (Zr0.66Y0.17Ta0.17O2, ZYTO) as a potential CMAS‐resistant material for TBCs, which shows a significantly enhanced CMAS resistance than the conventional 17 mol% YO1.5‐stabilized ZrO2 (17YSZ). After exposure at 1300°C for 100 hours, the CMAS infiltration depth in ZYTO bulk is ~80 μm (for a 20 mg/cm2 CMAS deposition), in contrast to ~700 μm in 17YSZ bulk (50 hours). Compositional and morphological analyses on the CMAS reaction zone reveal that the excellent CMAS resistance of ZYTO originates from the uniform corrosion through grain and grain boundary, along with densification of the reaction layer. The high CMAS infiltration rate of 17YSZ is attributed to the severe dissolution and infiltration through grain boundary. The reaction mechanisms of CMAS with ZYTO and 17YSZ bulks are discussed and a strategy of enhancing the CMAS resistance is proposed for ZrO2‐based TBC materials.

Sintering resistance of La2Ce2O7, La2Zr2O7, and yttria stabilized zirconia ceramics

La2Ce2O7 (LC), La2Zr2O7 (LZ), and yttria stabilized zirconia (YSZ) nanostructured powders with different agglomerate structures were successfully synthesized via wet-chemical method, and their high-temperature sintering resistance was systematically studied in this paper. Experimental results indicate that the synthesized nanostructured YSZ sample possessed the highest sintering resistance while nanostructured LC sample had the lowest sintering resistance. Theory of sintering process at initial stage was used to analyze experimental results. Sintering abilities of materials were closely related to their surface energy, lattice and grain boundary diffusion coefficients, and powder morphologies. Moreover, intrinsic sintering resistance (ISR) and extrinsic sintering resistance (ESR) were defined to further clarify the experimental results. ISR is determined by surface energy, lattice and grain boundary diffusion coefficients of the material, while ESR is affected by dimensions and density of raw powders. The highest sintering resistance of YSZ originated from dense initial powder with large size, which led to extraordinary ESR of the sample. ISR of LZ was found to be much better than that of YSZ and LC, while ISR values of LC and YSZ were similar. Finally, as ISR ability of thermal barrier coating (TBC) materials can be clarified by studying the corresponding crystalline size evolution, a feasible approach was proposed to compare ISR ability of novel TBC materials.

Na2SO4 + V2O5 Corrosion Behavior of BaNd2Ti3O10 for Thermal Barrier Coating Applications

BaNd2Ti3O10 has been considered as a promising thermal barrier coating (TBC) candidate material, which reveals many advantages over the widely used TBC material of yttria partially stabilized zirconia, such as lower thermal conductivity, better high-temperature capability, and higher resistance to environmental deposits corrosion. In this study, the hot corrosion behavior of BaNd2Ti3O10 in Na2SO4 + V2O5 molten salt at 900 °C and 1000 °C is investigated. Exposed to the salt for 4 h at 900 °C, BaNd2Ti3O10 pellets had an obvious reaction with the salt, forming corrosion products of NdVO4, TiO2, and BaSO4, and the reaction layer was ~30 μm, beneath which no salt trace could be found. Prolonging the corrosion time to 20 h, the type of the corrosion products had no change. At an elevated corrosion temperature of 1000 °C for 4 h, the corrosion products were still NdVO4, TiO2, and BaSO4, but NdVO4 revealed a significant growth, which fully covered the pellet surface. The mechanisms by which the corrosion reaction between BaNd2Ti3O10 and the molten salt occurred were discussed.