Thermal Barrier Coatings Material Research Articles

High-temperature oxidation behaviours of rare earth-based pyrochlore structured A2B2O7/yttria-stabilized zirconia thermal barrier coatings

Addressing the challenge of cost-effectively synthesizing stable thermal barrier coating materials has been a significant hurdle. This study describes the bulk synthesis of stannate-based pyrochlore compounds, specifically erbium tin oxide (Er2Sn2O7) and yttrium tin oxide (Y2Sn2O7). These synthesized pyrochlore oxides and commercially available yttria-stabilized zirconia (YSZ) were coated onto nickel super alloy. The coated specimens were subjected to thermal oxidation kinetics studies at 900 ± 5°C for 200 h, and alterations in physico-chemical characteristics, modifications in surface morphology, and variations in the composition of thermal barrier coating (TBCs) before and after exposure to oxidation conditions were evaluated. Oxidation kinetics results demonstrate that Er2Sn2O7 pyrochlore oxide has better performance than other Y2Sn2O7 and commercial YSZ TBC materials in high-temperature thermal barrier systems.

Unveiling thermal stresses in RETaO4 (RE = Nd, Sm, Eu, Gd, Tb, Dy, Ho and Er) by first-principles calculations and finite element simulations

Thermal stress (σ) plays a critical role in regulating the stability and durability of thermal barrier coatings (TBCs) during service. However, its measurements are limited due to technical challenges. Here, thermal stresses in RETaO4 (RE = Nd, Sm, Eu, Gd, Tb, Dy, Ho, and Er) TBCs have been evaluated by a cross-scale model, integrating first-principles calculations and finite element simulations (FEM). The isobaric heat capacity, thermal expansion coefficients, density, Young's modulus, and Poisson's ratio of RETaO4 as a function of temperature have been determined by the quasi-harmonic approach (QHA) and the quasi-static approach (QSA). Taking these properties as the input data of FEM, the σ of TBCs with RETaO4 as ceramic coatings is estimated. It indicates that the maximum tensile stress exists at the ceramic and thermal-grown oxide coating interface. Notably, TBCs_NdTaO4 exhibits the highest tensile stress, reaching up to 2093 MPa, while TBCs_GdTaO4 has the lowest value at 1880 MPa. Furthermore, the key factors affecting σ are estimated using interpretable machine learning based on the decision tree algorithm. The RETaO4 with small Poisson's ratio, strong electronegativity, small heat capacity, and thermal expansion coefficients is helpful to achieving low σ in TBCs. GdTaO4, YTaO4 and (Ho0.5Er0.5)TaO4 emerge as more favorable options as ceramic layer due to their lower σ in TBCs. This present cross-scale model provides a successful tool for predicting σ and the reverse design of TBCs materials based on low σ in TBCs.

Influence of doping elements on thermo-physical properties of co-doped strontium zirconate for potential thermal barrier coatings

Strontium zirconate is a promising material for thermal barrier coatings due to some excellent properties. New four co-doped strontium zirconate with lower thermal conductivity and higher thermal expansion coefficient were synthesized in this study. Sr(Zr0.9Y0.05Yb0.05)O2.95 (SZYYb) with the smallest difference in ionic radius and mass has lowest thermal diffusion coefficients mainly due to the effect of extrinsic phonon scattering mechanisms, including lattice distortion and grain size. The electronic structures of four co-doped SrZrO3 were analyzed by first-principles calculations. The findings suggested that the difference in bond strength caused by different doping affected the differences in the lattice constant, which led to the highest thermal expansion coefficient of SZYYb.

Preparation and high-temperature performance of Sc2O3–Y2O3 co-stabilized ZrO2 thermal barrier coatings

As a promising material for the advanced thermal barrier coatings (TBCs), scandium oxide (Sc2O3) and yttrium oxide (Y2O3) co-stabilized zirconia (ScYSZ) has been given increasing attention during the past decade. In this study, three types of TBCs including YSZ, ScYSZ and ScYSZ-YSZ double ceramic layer (DCL) coatings were deposited by a wide-velocity range high-energy plasma spraying technology. The thermal physical property, phase stability and thermal cycling performance of TBCs were comparatively studied. The results suggested that the thermal conductivity from 200 °C to 1000 °C of ScYSZ coating was reduced by approximately 30 % compared to the YSZ coating. After exposure at 1400 °C for 1000 h, the ScYSZ coating still kept the initial tetragonal phase structure, while the tetragonal phase was completely disappeared in the YSZ coating after 300 h at 1400 °C. Notably, the ScYSZ-YSZ DCL coating demonstrated the highest thermal cycling life within the temperature range of 1320∼1370 °C, exhibiting a remarkable 43 % increase over the single ScYSZ coating and doubling that of the single YSZ coating. The outcomes of this study hold significant promise for practical applications in the realm of high-performance TBCs.

DFT simulation to study the physical properties of ternary intermetallic materials ACuSb (A=Ca, Sr, Ba) for solar cell and TBC materials

This study carried out the configurational, bulk, electronic, optical as well as thermodynamic features of ternary materials ACuSb (A = Ca,Sr, Ba) using first-principles DFT-based calculations. The explored lattice constants as well as unit cell volume are very close to hypothetical results which make sure the correctness of the present study. According to the investigated elastic stiffness constants, the studied compounds are mechanically stable as they hold the Born's stability criteria. Utilizing the calculated values of elastic constants the several polycrystalline parameters such as elastic moduli (B, Y, E), machinability index (μm), hardness (HV), Poisson's ratio, Pugh's and isotropic/anisotropic factor of ACuSb (A = Ca,Sr, Ba) have been calculated and discussed in details. Very high machinability indices of these phases ensure their industrial applications. Since the values of Poisson's and Pugh's are ν < 0.26 and B/G < 0.75, therefore the phases ACuSb (A = Ca,Sr, Ba) show brittle manner. The direction-dependent features of these materials are confirmed from the Universal anisotropy factor analysis. Band structure analysis reveals that every compounds exhibit metallic character. Bond population analysis revealed the different covalent and ionic bonding tendencies in these compounds, with apparent differences in the nature of Cu–Sb bonds. Furthermore, the absorption coefficients of BaCuSb ensures its excellent suitability for solar cell applications, as it demonstrated remarkable UV-range absorption capabilities, distinguishing it from the other compounds in this regard. The thermal analysis demonstrated that these compounds exhibit remarkably low thermal conductivity, indicating their appropriate applications in thermal barrier coating (TBC) materials.

Searching for low thermal conductivity materials for thermal barrier coatings: A theoretical approach

Searching for low thermal conductivity materials for thermal barrier coatings: A theoretical approach

Improved thermal properties and CMAS corrosion resistance of high-entropy RE zirconates by tuning fluorite-pyrochlore structure

The order-disorder transition (ODT) of RE zirconate (RE2Zr2O7) has received much attention due to its potential applications in the design of thermal barrier coatings (TBCs). A series of high entropy RE zirconates (RE = La, Sm, Gd, Er and Lu) were designed and synthesized in order to regulate the fluorite-pyrochlore phases, and to investigate the effect of phase composition on the microstructures and performances. The results showed that the sintering temperature, as well as equivalent ion radius, played an important role in regulating the phase transformation of fluorite-pyrochlore. The coexistence of pyrochlore-fluorite phases not only can result in the decrease in grain size but also increased the lattice strain of each phase, thereby enhancing the phonon scattering and contributing to the reduction in the thermal conductivity. The CMAS corrosion resistance was mainly related to phase compositions, and the thicknesses of reaction layer decreased gradually with the increasing fluorite phase content. The results will provide theoretical guidance for the microstructural design of high entropy RE zirconates as next generation TBC materials in future.

Stability and physical properties of two novel magnetic MAX phase compounds Fe2AB (A=Cu and Zn) from density functional theory

MAX phases exhibit a wide range of important physical properties, making them a significant area of research with various practical applications. In this paper, a theoretical study of two new magnetic MAX phases, Fe2CuB and Fe2ZnB, has been conducted using first-principles spin-polarized calculations. The focus is on exploring their structural, electronic, magnetic, elastic, mechanical, and thermodynamic properties in the hope of identifying attractive properties for potential technological applications. It has been found that Fe2CuB and Fe2ZnB are thermodynamically, dynamically, and mechanically stable. They are predicted to be ferromagnetic ductile and exhibit a degree of elastic anisotropy. Moreover, examination of the density of states (DOS) curves reveals the metallic and magnetic properties of the materials. Fe2CuB and Fe2ZnB exhibit total magnetic moment values of 7.77 μB and 6.47 μB, respectively. The significant difference in Curie temperatures between Fe2CuB and Fe2ZnB, with values of 1194 K and 310 K, highlights distinct thermal stability characteristics inherent in these MAX phases. We have discovered that Fe2ZnB is a promising candidate for high-temperature spintronic applications, while Fe2CuB may be suitable as a material for thermal barrier coatings (TBC) due to its low minimum thermal conductivity.

A strategy for low thermal conductivity of lutetium oxyorthosilicate ceramics fabricated via texture engineering

AbstractSubmicrometer lutetium‐gadolinium oxyorthosilicate ((Lu0.95Gd0.05)2SiO5, LGSO) powder with a magnetic susceptibility of 4.19 10−6 (5.4 times that of lutetium oxyorthosilicate) was synthesized via a sol‐gel method. Slip casting with a 6 T assisted magnetic field and pressureless sintering at 1600°C for 16 h in the air effectively produced the textured LGSO ceramics with an orientation factor f of 0.96. The grains of textured LGSO ceramics grow with the preferred orientation along the b‐axis. The thermal conductivity of the textured LGSO ceramics reaches only 2.05 W·m−1·K−1 at 300 K, which is 34.5% lower than that of untextured LGSO ceramics. Textured LGSO ceramics provide increased fracture toughness. This work presents a microstructural design method for RE2SiO5 ceramics to regulate thermal and mechanical properties through texture engineering, as well as advice for the selection or optimization of RE2SiO5 ceramics as a Thermal Barrier Coatings (TBCs) material.

High-entropy (La0.2Dy0.2Er0.2Yb0.2Y0.2)2Zr2O7 oxide, a potential thermal barrier coating material with photoluminescence property sensitive to pressure

In this work, high-entropy (La0.2Dy0.2Er0.2Yb0.2Y0.2)2Zr2O7 oxide (RZHEO-1600) has been synthesized by using a simple solid-state reaction method and investigated as a promising thermal barrier coating (TBC) material with potential optical pressure sensing application. Compared to oxide-yttria stabilized zirconium (YSZ) and single component zirconates, RZHEO-1600 exhibits excellent thermal stability at 1600 °C and a larger thermal expand coefficient 13.5 × 10−6 K−1 due to the high entropy effect. Its thermal conductivity (1.23–1.41 W m−1 K−1) and Vickers hardness (10 GPa) are lower than YSZ, while its fracture toughness (2.9 MPa m1/2) is much larger. The photoluminescence (PL) emissions of RZHEO-1600 excited by 514 nm laser are assigned to 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions of Er3+ ions. The centre positions of emission peaks initially at 560 and 677 nm are sensitive to pressure, which red shift linearly with pressure coefficients of 0.178 nm/GPa (−5.650 cm−1/GPa) and 0.223 nm/GPa (−4.932 cm−1/GPa), respectively. Interestingly, the PL intensity ratios I677/I658 and I560/I547 are found to be pressure sensitive, which continuously increase during the compression. The findings of this study could serve as a new guide for the development of novel high-entropy oxide TBC materials with optical sensing applications.

Interaction laws of RE2O3 and CMAS and rare earth selection criterions for RE-containing thermal barrier coatings against CMAS attack

Thermal barrier coatings (TBCs) with higher rare earth (RE) contents are more resistant to CaO-MgO-Al2O3-SiO2 (CMAS) attack due to their reaction to form apatite protective products. In this study, the reaction behavior between RE2O3 and CMAS was investigated and their interaction laws were clarified, based on which three criterions for selecting RE dopants for RE-containing TBC materials are proposed: 1) favorable reaction product types and strong protective products formation kinetics, 2) low RE3+ solubility in molten CMAS, and 3) low wettability of residual mixture. Sm2O3 and Gd2O3 are demonstrated as the most attractive dopants for RE-containing TBCs against CMAS attack.

Effect of Gd doping on phase evolution, mechanical and thermal characteristics of 1La-xGd-2Yb-3.5YSZ solid solutions

Thermal barrier coatings (TBCs) are critical for the reliability and lifespan of aircraft engine turbine blades. In this study, a novel quaternary rare-earth oxide (La2O3, Gd2O3, Yb2O3, and Y2O3) co-doped ZrO2 solid solution, referred to as 1La-xGd-2Yb-3.5YSZ, was synthesized by varying the doping amount of Gd2O3 from 0 to 6 mol. %. The impact of co-doping-induced lattice distortion on the phase composition, high-temperature phase stability, sintering resistance, and mechanical and thermal properties of the solid solution has been explored. It is found that the addition of Gd2O3 stabilizer effectively increased the lattice distortion of the solid solution, which led to improved phase stability and sintering resistance, enhanced mechanical properties, and low thermal conductivity. Our findings highlight the promising properties of the 1La-xGd-2Yb-3.5YSZ solid solution, making it an attractive candidate for TBC materials.

Formation of Phases and Mechanical Properties of YSZ-Based Thermal Barrier Coating Materials Doped with Rare Earth Oxides

Formation of Phases and Mechanical Properties of YSZ-Based Thermal Barrier Coating Materials Doped with Rare Earth Oxides

Effects of GdTaO4 content on the thermal properties and CMAS corrosion of Gd2Zr2O7-GdTaO4 composite ceramics

Thermal barrier coating materials play a crucial role ensuring the efficient and stable operation of gas turbines. The thermophysical and mechanical properties of GZ1-x-GTx (x = 0, 0.1, 0.3, 0.5) composite ceramics, as well as the corrosion resistance properties against calcium magnesium aluminum silicate (CMAS) at 1250 °C, were investigated. The results indicated that the overall properties of Gd2Zr2O7-GdTaO4 composite ceramics significantly improved with an increase in the second phase GdTaO4 content. Among all the ceramics designed, GZ0.5-GT0.5 exhibited the lowest thermal conductivity (0.920 W m−1 K−1 at 800 °C) and the highest fracture toughness (2.02 MPa m1/2). Additionally, the molten CMAS interacted with the Gd2Zr2O7-GdTaO4 composite ceramics, forming a dense apatite layer, which positively contributed to inhibiting CMAS infiltration. Considering its excellent thermal, mechanical, and corrosion resistance properties, Gd2Zr2O7-GdTaO4 composite ceramics are considered a promising material for thermal barrier coatings.

Structure, thermal and mechanical properties of mid-entropy thermal barrier ceramic (Y0.3Gd0.3Yb0.4)4Hf3O12 prepared by ultrafast high-temperature sintering

Thermal barrier coatings (TBCs) have an important role to play in the development of aero engines. In this paper, mid-entropy rare-earth hafnate (Y0.3Gd0.3Yb0.4)4Hf3O12(YGYbH) ceramic material was designed based on rRE3+/rHf4+ and was successfully fabricated in only 7 min using an ultrafast high-temperature sintering (UHS) process. The YGYbH ceramic bulk exhibits a single homogeneous fluorite structure and excellent high temperature phase stability, which can remain phase constant for 80 h at 1500 °C due to its unique cation radius ratio and high-entropy effect. YGYbH possesses sluggish grain growth characteristics and great anti-sintering properties, and when annealing at 1500 °C for 30 h, its grain size only grows from the initial 1.19 μm–1.61 μm, which is conducive to stabilizing the mechanical properties of YGYbH at higher service temperature. YGYbH has a low thermal conductivity of 0.89 W/(m·k) at 1100 °C, which is much lower than that of 6%–8%Y2O3 partially stabilized ZrO2(YSZ) (∼2.5 W/(m·k)), while having a high coefficient of thermal expansion (CTE), from 8.8 × 10−6/K at room temperature to 11.0 × 10−6/K at 1500 °C which is nearly to that of the YSZ. Furthermore, YGYbH has a high hardness (11.94 GPa) and a low elastic modulus (147.4 GPa), but a slightly lower fracture toughness (1.26 MPa m½) than that of 8YSZ, exhibiting great overall mechanical properties. Based on the results of this work, YGYbH with excellent overall performance exhibits great potential as the next-generation TBC material.

High-Throughput screening of inorganic lead-free halide perovskites CsCu2X3 (X = Cl, Br, I) for optoelectronics applications

This study effectively explores in detail the structural, optical, electronic, elastic, mechanical, lattice vibrational and thermodynamic features of orthorhombic CsCu2X3(X = Cl, Br, I) perovskites using first-principles calculations. Formation energy, Born stability criterion, and phonon dispersion validated our compounds thermodynamic, mechanical, and dynamical stability. All the studied compounds possess significant elastic anisotropy and are fairly machinable with CsCu2I3 are relatively hard than the other two. UV light can be efficiently absorbed by CsCu2X3(X = Cl, Br, I) compounds. Due to their strong UV reflectivity, all the compounds have the potential to be utilized as shielding to reduce solar heating by up to ∼ 20 eV with CsCu2Cl3 being more efficient. The compounds under study have low Debye temperatures, low melting points, and low minimum phonon thermal conductivities. Relatively low values of Debye temperature and minimum thermal conductivity for CsCu2X3 making them potential as thermal barrier coatings (TBC) materials.

Interactions between rare-earth zirconates (RE2Zr2O7) and CMAS silicate melts

Rare-earth zirconates (RE2Zr2O7) are potential thermal barrier coatings (TBCs) candidates exhibiting excellent thermal insulation property to protect underlying superalloy substrate. These coating materials, however, are subjected to degradation caused by molten silicon-containing sand dust and volcanic ash whose main compositions are CaO-MgO-AlO1.5-SiO2 (brief to CMAS) at higher operating temperatures (> 1200ºC). Here, we have studied the thermochemical interactions between three RE2Zr2O7 (Sm2Zr2O7, Gd2Zr2O7 and Yb2Zr2O7) and CMAS with three different compositions (referred to as CMAS-1, CMAS-2 and CMAS-3, respectively) at 1300ºC/30 min. Both the diversities of the REO1.5 identity and CMAS composition result in the precipitation of apatite with varying stoichiometry. For an equivalent CMAS case, there is a linear correlation between the apatite content and the RE cation radius. In CMAS-1, the Ca:RE ratio of apatite observed in the Sm2Zr2O7 case is ∼0.31, larger than that of Gd2Zr2O7 (∼0.30) and Yb2Zr2O7 (∼0.20). Additionally, the RE3+ solubility in equilibrium with apatite decreases with the increased CaO content from CMAS-3 to CMAS-1 for a given RE2Zr2O7 material, facilitating the apatite precipitation within a short time. For example, in Sm2Zr2O7 case the Sm3+ solubility decrease from ∼3.18 at % to ∼0.70 at % as the CaO content increases from 19 mol % ( in CMAS-3) to 33 mol % ( in CMAS-1). Also, the composition of residual CMAS melt changes as the interaction proceed, which can impact its flow property and infiltration propensity. These finds may advance the design of current and next-generation TBCs material and development of effective strategies to mitigate the CMAS-induced coating failure.

Numerical investigation of thermomechanical behavior of Yttrium barium zirconate-coated aluminum alloy piston in an internal combustion engine

Increasing engine power to volume density is under investigation and being analysed extensively. Turbocharger, which is used to boost volumetric efficiency, also raises cylinder temperature and pressure, thus resulting in thermal distortions and reducing clearances in tribo-contacts, thereby compromising engine life. Thermal barrier coatings (TBCs) have shown potential to provide remedies to reduce heat losses, hazardous emissions, and heat flow toward the piston skirt in an internal combustion engine. In this study, a detailed thermo-mechanical analysis was performed for a diesel engine piston with a novel yttrium barium zirconate (YBZ) coating and then compared with other TBCs with varying thicknesses. The results revealed a notable decrease in piston substrate surface temperature when coated with various TBCs, with YBZ coating demonstrating superior performance over others. The 0.2 mm coating of YBZ-coated piston exhibited significant reductions of 15% and 10.3% in temperature and thermal stress respectively, thus enhancing piston durability. The better performance of the novel YBZ coating could be attributed to its stable thermal and elastic properties and lower thermal conductivity than other TBC materials. YBZ coating provides a promising solution to improve engine efficiency while extending engine life, making it an attractive option for the automotive industry.

Damage Grading Evaluation of Thermal Barrier Coatings under CMAS Corrosion

Thermal barrier coatings (TBCs) material has excellent high-temperature resistance and heat insulation performance, which plays a vital role in improving the working efficiency and running life of the engine. During the flight, the engine will inhale dust particles in the air. These particles are mostly from siliceous debris, which are usually called calcium magnesium aluminum silicate (CMAS). At present, CMAS corrosion has become one of the important problems affecting the service life of thermal barrier coatings. In this study, conventional yttrium oxide stabilized zirconia (YSZ) coatings and ytterbium oxide and yttrium oxide co-stabilized zirconia (YbYSZ) coatings were prepared by atmospheric plasma spraying. The two coatings were examined under thermal cycling-CMAS coupling conditions and divided into six life stages. The failure modes, CMAS permeation behavior, crack characteristics and mechanical properties of the two coatings at different life stages were evaluated systematically. The experimental results show that the YbYSZ coating has a longer life than YSZ coating under the thermal cycling and CMAS coupling condition, which increases by about 83% compared with the conventional YSZ coating. In the whole life stage, the porosity of YbYSZ coating is always higher than that of YSZ coating. The phase transition is not the reason for the failure and spalling of the coatings. The crack length of the two coatings showed an increasing trend, but the crack length of the YSZ coating was higher than that of the YbYSZ coating, and the crack density of the two coatings showed a “saddle shape”, which was more obvious for the YSZ coating. The YbYSZ coating shows better mechanical properties under the thermal cycling-CMAS coupling condition with the evolution of life.

Sintering resistance and phase stability of (Y0.2La0.2Nd0.2Sm0.2Eu0.2)2Zr2O7 for ultra-high temperature thermal barrier coatings

High-temperature stability, including sintering resistance and phase stability, is critical for thermal barrier coatings (TBCs) applied at ultra-high temperature over 1500 °C. In this work, we reported a high-entropy rare-earth zirconate (Y02La0.2Nd0.2Sm0.2Eu0.2)2Zr2O7 (YLNSE) synthesized by solid-state reaction method. X-ray diffraction (XRD), transmission electron microscopy (TEM), and energy dispersive spectrometer (EDS) mapping results confirmed that YLNSE formed a single-phase pyrochlore structure with uniform rare earth elements distribution. YLNSE maintained more uniform microstructure, higher porosity retention, lower grain growth rate and better thermomechanical properties during sintering at 1500 °C, as the results of the ordered crystal structure and sluggish diffusion effect, indicating a better sintering resistance than conventional TBC material yttria-stabilized zirconia (YSZ). In addition, YLNSE also demonstrated high coefficient of thermal expansion (CTE, 11.04 × 10-6K-1, 25–1500 °C) and low thermal conductivity (1.95 W m-1 K-1, 1500 °C), as well as good phase stability at 1500 °C. In view of the excellent high-temperature stability of YLNSE, it is a promising candidate for ultra-high temperature TBCs.