The corrosion of calcium-magnesium-aluminosilicate (CMAS) is a critical degradation mechanism for the hot sections of aircraft engines, particularly affecting abradable components where inherent defects complicate the prevention of rapid CMAS melt penetration. To address this challenge, Ti3AlC2 was incorporated into the porous LaMgAl11O19 abradables at concentrations of 5-20 wt% as both a self-healing agent and sintering aid. Annealing at 1200 degrees C markedly improved crack closure and pore isolation within the coating, with these effects intensifying with higher Ti3AlC2 concentrations, and resulted in the retention of excess TiO2. CMAS interaction tests conducted at 1300 degrees C demonstrated that only the abradables with 20 wt% Ti3AlC2 addition significantly reduced the penetration of CMAS melt. This effect is attributed to the densification of the abradables caused by self-healing, which blocks the propagation of CMAS along defect channels, and the role of TiO2 as a nucleating agent that facilitates the crystallization of CMAS and the precipitation of CaAl2Si2O8. The La/Ca ratio in the solid solutions related to LaMgAl11O19 and LaTi2Al9O19 can be used to reflect the corrosion level of platelet-like grains, where a value below 1 is likely to trigger their dissolution.

YbTaO4-Ta2O5 composites were designed and different multi-layered YbTaO4-Ta2O5/Yb2Si2O7/Si (YbT-T/YbDS/Si) as well as YbTaO4-Ta2O5/Si (YbT-T/Si) environmental barrier coatings (EBCs) were put forward to protect SiC fiber reinforced silicon carbide (SiCf/SiC) ceramic matrix composites (CMCs). The thermal cycling and the water-vapor/oxygen corrosion behavior of different multi-layered EBCs were compared. Results indicated that the thermal cycling lifetime of the bi-layered YbT-T/Si EBCs was similar with the tri-layered YbT-T/YbDS/Si ones. The ultimate failure of these two EBCs was induced by the cracking of the SiCf/SiC substrates as well as the vertical cracks associated with the thermal mismatch stress among different layers. However, the tri-layered EBCs exhibited greater resistance to water-vapor/oxygen corrosion than the bi-layered ones, primarily due to that the tri-layered YbT-T/YbDS/Si EBCs contained significantly less cracks than the bi-layered ones, limiting the transport of reactant (oxygen and/or water vapor) to reach Si bond coat.

In this study, the garnet -type Yb3Al5O12 coating was fabricated by atmospheric plasma spraying and its properties were systematically investigated. Results show the as-sprayed coating consists of crystalline Yb3Al5O12 with amorphous phase, recrystallization occurs at 918.5 degrees C accompanied by a 0.32% volume shrinkage. Yb3Al5O12 coating demonstrates low thermal conductivity (2.1 W/(m center dot K) at 1000 degrees C) coupled with a moderate thermal expansion coefficient (8.87 x 10-6 K-1 from 200 degrees C to 1400 degrees C). Additionally, Yb3Al5O12 coating displays remarkable structure stability and sintering resistance at elevated temperatures. Its robust corrosion resistance can be demonstrated by rapidly generating dense anorthite layers during CMAS corrosion and the lack of a discernible corrosion layer in water vapor corrosion. Yb3Al5O12/YSZ TBC undertakes a thermal cycling lifetime of 970 cycles, superior to YSZ of 764 cycles. This improvement is primarily ascribed to lower oxygen permeability of garnet layer. These preliminary results indicate that Yb3Al5O12 coating might be suitable for advanced TBC applications.

The study aims to investigate the influence of infrared emissivity on thermal barrier coating (TBCs) for service applications. Two double-layer TBCs, namely RMgAl11O19/YSZ (marked as RMA/YSZ, R=La, Pr) and conventional single-layer YSZ TBCs, were comparatively tested using a burner rig facility. The microstructure, infrared emissivity, and thermal cycling performance of the three TBCs were investigated. The results demonstrate that the emissivity of PrMA/YSZ has been improved by approximately 20% compared to LaMA/YSZ in the wavelength range of 2-6 mu m, owing to an improvement in electronic transition. Due to higher emissivity, the surface temperature of PrMA/YSZ decreased by 70 degrees C under the same heat flux, leading to a reduction in coating aging and substrate temperature. Accordingly, PrMA/YSZ exhibited the highest thermal cycling lifetime among the three coatings.

An Al film was deposited onto the surface of yttria-stabilized zirconia (YSZ) coating using magnetron sputtering, followed by in situ oxidized to form Al2O3, referred to as Al2O3-YSZ (A-YSZ). The corrosion behavior of the A-YSZ coating against the attacks of calcium-magnesium-aluminum-silicon (CMAS) and a composite corrosive agent containing salt (NaVO3/Na2SO4/NaCl) and CMAS (CMAS + salt). Results demonstrate the excellent resistance of the investigated coating to the corrosion of CMAS and CMAS + salt. The Al2O3 layer plays a crucial role as sacrificial protection in effectively isolating the composite corrosive agents, substantially extending the service life of YSZ coatings. NaVO3, Na2SO4, and NaCl promote the formation of high-melting-point products, reducing their penetration into the YSZ layer. The reaction mechanisms of Al2O3 with CMAS and CMAS + salt were clarified.

An exploration of the plasma-sprayed abradable sealing coatings (ASCs) of a thick and porous LaMgAl11O19 topcoat onto SiC/SiC ceramic matrix composites (CMCs) is detailed in this study. Interlayers comprising Si/Si + Yb2Si2O7/Yb2SiO5 environmental barrier coatings (EBCs) were strategically employed, considering their function in protecting the SiC/SiC CMCs from recession and mitigating thermal expansivity misfit. An isothermal oxidation test was conducted at 1300 °C and resulted in the formation of bubble and glassy melt on the side surface of the coated sample, while a significant reaction layer emerged at the Yb2SiO5/LaMgAl11O19 interface near the edge. The localized temperature rise caused by the exothermic oxidation of the SiC/SiC substrate was determined to be the underlying factor for bubble generation. The temperature-dependent viscosity of the melt contributed to various bubble characteristics, and due to the enrichment of Al ions, the glassy melt exacerbated the degradation of the Yb2SiO5 layer. After a thermal shock test at 1300 °C, the substrate on the uncoated backside of the sample experienced fracture, while the front coating remained intact. However, due to the presence of a through-coating crack, an internal crack network also developed within the substrate.

Perovskite-type aluminates hold significant promise for applications as thermal protective coatings (TPCs), but their inferior properties necessitate further optimization. In this study, PrAlO3+delta (PA) and Sr2+ doped Pr1-xSrxAlO3+delta (PSA, x = 1, 2, 5 mol%) were fabricated using the solid-state reaction method. The effects of Sr2+ substitution on properties were thoroughly investigated. The results demonstrated pronounced effects of Sr2+ substitution. PSA exhibited significant lattice volume expansion and enhanced sintering resistance with increasing doping concentration. Also, doping strategy effectively decreased thermal conductivity of PSA 4.38 W/(m center dot K) at room temperature to 3.48 W/(m center dot K) at 900 C-degrees, decreasing by about 15% in comparison to that of PA (6.21-4.07 W/(m center dot K)). Moreover, mechanical properties of PSA were improved, presenting the lowest elastic modulus (118.7 GPa) in contrast to that of PA (344.3 GPa). Most importantly, despite the lattice distortion caused by doping leading to limited improvement in infrared emissivity in the range of 8-14 mu m, the infrared emissivity of PSA was significantly enhanced in the range of 3-5 mu m. A highest average emissivity of 0.875 was achieved with x = 2 mol%, representing a 10 % enhancement compared to that of PA (0.796). Furthermore, the enhancement mechanisms were systematically elucidated.

Introduction of luminescent rare earth ions into thermal barrier coatings (TBCs) for the study of TBCs failure mechanism is a very effective non-destructive method. In this paper, Eu3+ ions were doped into La-2(Zr0.7Ce0.3)(2)O-7 (LZ7C3) to form LZ7C3:Eu fluorescent material using a high-temperature solid-phase synthesis method. By analyzing the physical structure, fluorescence properties and thermophysical properties of LZ7C3:Eu powders synthesized with different Eu3+ dopant concentrations at different temperatures, we determined that a synthesis temperature of 1400 degrees C, a dopant concentration of 1 mol% are the optimal synthesis conditions for LZ7C3:Eu. Independent LZ7C3:Eu coating was prepared by atmospheric plasma spraying technology, and high temperature aging test was carried out at 1400 degrees C. The influence of high temperature aging on the D-5(0)-> F-7(2) energy level transition peak of Eu3+ in LZ7C3 powder and its coating was examined by microscopic emission spectroscopy. The results show that the peak of the D-5(0)-> F-7(2) energy level transition is red-shifted, and the peak intensity and the full width at half maxima (FWHM) of the powder decrease gradually with the increase of high temperature aging time. The peak of the D-5(0)-> F-7(2) energy level transition of the coating exhibits a constantly fluctuating tendency of red-shifting and then blue-shifting, and the peak intensity and the FWHM also continue to decrease. High temperature aging has a negative effect on the fluorescence properties of LZ7C3:Eu materials.

Defects such as interconnected pores and cracks can improve the abradability of ceramic-based abradable sealing coatings (ASCs) but may reduce the lifetime. Self-healing can potentially close cracks and transform interconnected pores into isolated ones through filling and sintering effects. Ti3AlC2 (TAC) was incorporated into LaMgAl11O19 (LMA) as both the self-healing agent and sintering aid, and plasma-sprayed LMA-based composite coatings were annealed at 1200 °C to assess their self-healing capabilities and then subjected to oxidation in air and corrosion in steam at 1300 °C to study their long-term stability. Results indicated that increasing TAC content significantly enhances self-healing effectiveness, evidenced by the closure of cracks and the isolation of pores. Oxidation and corrosion at 1300 °C led to significant grain growth and the formation of equiaxed grains with an aspect ratio of approximately 3, which may impair the toughening mechanism. Meanwhile, due to the preferential volatilization of Al in a steam environment, LTA decomposed into α-La2/3TiO3 and La4Ti3O12 phases, and the accelerated mass transfer also resulted in grain coarsening. Interestingly, the L20T composite coating with a porosity of 32.17 ± 0.94% and a hardness of 74.88 ± 1.55 HR15Y showed great potential for abradable applications due to its stable phase composition and uniform pore distribution.

LaMgAl11O19 (LMA) with magnetoplumbite structure has emerged as a promising candidate for thermal barrier coating (TBC). However, the inherent high thermal conductivity and relatively low thermal expansion coefficient (TEC) of LMA impose limitations on its further application. In this work, a novel high-entropy hexaluminate (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)MgAl11O19 (HE-LMA) has been designed and prepared to overcome these obstacles. HE-LMA with homogeneous chemical composition distribution possesses excellent phase stability up to 1600ºC. Moreover, the TEC of HE-LMA (9.22 × 10-6K-1 at 1300ºC) is larger than that of LMA. The high-entropy strategy effectively decreases the thermal conductivity of HE-LMA (from 3.27W/(m∙K) at room temperature to 2.19W/(m∙K) at 1000ºC) in comparison to that of LMA (3.63~2.62W/(m∙K)). Furthermore, HE-LMA demonstrates higher microhardness and fracture toughness due to the lattice distortion. These results indicate that (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)MgAl11O19 has the potential to be applied as a TBC.

Thermal radiation coating with low thermal conductivity and high infrared emissivity are desirable. In this work, a novel rare-earth aluminate (PrAlO3(+)(delta) with rhombohedral structure) was synthesized via solid-state reaction method, and the corresponding coating was fabricated using atmospheric plasma spraying (APS). The study encompassed an investigation into the phase structure, high-temperature phase stability, thermo-mechanical characteristics, and infrared properties. The results illustrate that as-deposited coating contained amorphous phase, but recrystallized coating presented phase stability up to 1600 degrees C. Furthermore, the recrystallized coating exhibited low thermal conductivity of 1.35 W/m K at 900 degrees C as well as an average coefficient of thermal expansion of 10.36 x 10(-6)/K. Also, the coating exhibited high infrared emissivity related to high valance state (Pr4+) and oxygen vacancies. And the average infrared emissivity within 2-14 mu m was 0.822 at 1300 degrees C and presented slight decrease with the increase of temperature (the average infrared emissivity of 0.795 at 1800 degrees C).

In recent years, the degradation of zirconia in a humid environment has attracted the attention of researching. In this work, Mg0.09Zr0.91O1.91 (MSZ), Y0.09Zr0.91O1.955 (YSZ) and Ce0.09Zr0.91O2 (CSZ) powders were prepared by co-precipitation method, the corresponding zirconia coatings were fabricated by atmospheric plasma spraying (APS). All coating samples were subjected to hydrothermal treatment to investigate their degradation process in moisture. The evolution of phase composition and microstructure were characterized. Results show that the content of monoclinic phase (m) in MSZ, YSZ and CSZ coating samples increased after hydrothermal treatment, rising by 47 % in MSZ coating, by 31 % in YSZ coating and by 8 % in CSZ coating. The degradation of internal structure of coatings was more serious with the prolongation of hydrothermal treatment time. This is because different stabilizers will cause different oxygen vacancy concentration in the zirconia unit cell, which determines the hydrothermal stability of zirconia. Under the tested condition, CSZ has the lower oxygen vacancy concen-tration (4 %) than MSZ (11 %) and YSZ (7 %), exhibiting better hydrothermal stability.

LaMgAl11O19 (LMA) with magnetoplumbite structure has been identified as a potential candidate for the next generation of thermal barrier coatings (TBCs). However, the as-sprayed LMA coating presents a large amount of amorphous phase originating from the rapid quenching from the molten droplets, which may compromise the reliability of coating during high-temperature service. A logical approach to improve LMA TBC life, therefore, is to enhance its crystallinity. In the present study, three LMA powders with different particle size distributions (fine, medium and coarse feedstocks) were utilized to deposit TBCs to investigate whether the thermal durability of LMA can be improved by increasing particle size. It was based on a hypothesis that large particle size can decrease the melting degree of in-flight particles and thus result in high crystallinity of as-sprayed LMA coating, making less recrystallization stress to enhance the thermal shock resistance of LMA coating. Results show that prolonged thermal cycling durability can indeed be achieved by increasing particle size. However, excessive particle size could lead to higher porosity derived from unmelted particles, which function as the weak regions for the coating system, thereby damaging the structural integrity and adhesive strength between the topcoat and bond coat. This could cause microcrack linking when the accumulated thermal stress exceeds its fracture toughness under consecutive heating-cooling cycles despite its higher crystallinity. Concerning the coating fabricated by medium powder, it achieves the optimal balance of crystallinity and structure integrity, resulting in the longest thermal cycling lifetime. The results provide guidance for the development and design of high thermal durability LMA TBCs. When optimizing the recrystallization stress within the coating, attention should be paid to improving its bonding strength simultaneously.

A study of porous YSZ abradable sealing coating (ASC) plasma-sprayed onto SiCf/SiC ceramic matrix composites (CMC) through the compatibility of intermediate layers is reported. The multilayer Si/Yb2Si2O7/LaMgAl11O19 thermal-environmental barrier coating (T-EBC) is served as intermediate layers in consideration of its ability to protect the CMC from recession and ease the misfit of the thermal expansivity. Isothermal exposure and thermal shock tests were conducted at 1200 degrees C and led to the decomposition of t'-ZrO2 phase to t-ZrO2 and c-ZrO2 phases in YSZ topcoat, the formation of mud-cracks throughout the entire coating structure and thermally grown oxide (SiO2), with following an Yb2Si2O7 reaction layer. The measured bond strength of the coated samples was 5.47 +/- 0.85 MPa, and the fracture position mainly happened inside the CMC substrate. The Superficial Rockwell Hardness (HR15Y) considered to be an important factor in abradability increased by only 1.34% after 1200 degrees C isothermal exposure for 100 h, showing excellent high temperature hardness stability. The abradability of the ASC was investigated by a sliding wear test, the fatigue wear mainly occurred in worn scar when encountering Si3N4 ceramic ball with high hardness and low thermal conductivity, while adhesive wear occurred when GCr15 steel ball with low hardness and high thermal conductivity are encountered.

In order to promote the thermal cycling behavior of SiCf/SiC composites at high-speed gas scour and high-temperature environment, we have prepared three-layer Si/Yb2SiO5/LaMgAl11O19 TEBCs onto the surface of SiCf/SiC composites using atmospheric plasma spraying (APS) method. Burner rig tests were performed to evaluate the thermal cycling behavior of TEBCs. Results show that after being tested in high-temperature and high-speed burner flame, only a small number of TEBCs cracked and peeled in the external area of TEBCs caused by the thermal stress and the corrosion of water vapor, but TEBCs did not crack and spall in the center area. The failure mechanism of TEBCs was investigated. Microstructure characterization indicated that the penetrating cracks in TEBCs provided the channel for oxygen and water vapor diffusion to SiCf/SiC composites leading to the severe corrosion of substrate.

In this study, a high-entropy RMgAl11O19 (HE-RMA, R = La, Pr, Nd, Sm, Gd) and LaMgAl11O19 (LMA) coatings were fabricated by atmospheric plasma spraying. The phase composition, microstructure, thermal stability, infrared emissivity performance and shock resistance were comparatively characterized. The results showed that doping multiple rare-earth cations could be conductive to enhance the infrared emissivity. The as-sprayed HERMA coating exhibited the highest infrared emissivity, which reached up to 0.971 at 1000 degrees C. The reason for the improvement of the infrared emissivity was attributed to introduced impurity energy level resulting from doping cations, which could reduce the forbidden bandwidth and increase probability of electronic transition. Meanwhile, HE-RMA coating exhibited better shock resistance at 1100 degrees C due to superior fracture toughness (1.84 +/- 0.41 MPa.m(1/2)) during thermal cycling test at 1100 degrees C. In addition, HE-RMA coating still exhibited high infrared emissivity (0.932 at 1000 degrees C) at 1100 degrees C annealing for 100 h with only a slight reduction.

The nanostructured (8 wt%) yttria stabilized zirconia coatings (n-YSZ) were deposited by atmospheric plasma spraying (APS) to study the effect of moisture degradation on the properties of n-YSZ coatings. Variations in phase composition, microstructure and mechanical properties were comprehensively characterized. The single -edge notched beam method used for fracture toughness testing is sufficiently reliable for evaluating the integral properties of the coatings in this study. Results indicated that the microstructure of the n-YSZ coatings was significantly affected by hydrothermal degradation. Hydrothermal degradation resulted in substantial defects, such as pores and cracks, which severely decreased the mechanical properties of the n-YSZ coatings. In addition, the ceramic coat was in a state of compressive stress, and the stress initially increased and then decreased with increasing degradation time. The variations in the stress of the n-YSZ coatings are closely related to the trans-formation of tetragonal to monoclinic phase, which is induced by hydrothermal degradation. Additionally, several major mechanical properties of the n-YSZ coatings decreased significantly with the hydrothermal degradation, including fracture toughness from 1.28 +/- 0.05 to 0.08 +/- 0.01 MPa m1/2, flexural strength from 60.51 +/- 2.98 to 4.54 +/- 0.14 MPa, and Young's modulus from 21.98 +/- 0.96 to 1.46 +/- 0.33 GPa.

Atmospheric plasma spraying (APS) process was employed to produce four-layer Si/Si-Yb2SiO5/Yb2SiO5/LaMgAl11O19 environmental barrier coatings (EBCs) for SiCf/SiC composites with SiC sealing layer. The bending strength of the specimens after isothermal oxidation was investigated. The specimens with EBCs especially thanks to the Si-Yb2SiO5 mixture layer showed a high bending strength retention rate with "psesudo-plastic" fracture. The Si-Yb2SiO5 mixture layer could remarkably enhance the oxidation resistance and also prolonged the life of the EBCs. Such obvious improvements in the Si-Yb2SiO5 mixture layer were attributed to that Yb2SiO5 reacted with TGO (SiO2) to in-situ form a dense Yb2Si2O7 layer, which was conducive to control the thickness of the TGO and prevent the prolongation of the cracks.

In this study, La1-xNdxMgAl11-xScxO19 (x = 0.1, 0.2, 0.3; abbreviated as LNMAS-1, 2, 3) coatings which are supposed to possess better properties than LaMgAl11O19 (LMA) were plasma-sprayed and their high-temperature performance were comparatively investigated. Results show that addition of Nd3+ and Sc3+ as dopants to LMA endows corresponding coatings with reduced thermal conductivity and enhanced thermal expansion coefficient, while maintaining advantageous phase stability, although still being subjected to amorphization in plasma flame and following crystallization upon high-temperature service. Furthermore, the doping could cause adherence increasing between topcoat/bondcoat, benefiting from improved melting condition, especially in LNMAS-2 and LNMAS-3 coatings, which is related to the specific powder morphology and lowered melting point. During exposure to 1350 degrees C, mechanical performance and structure integrity of doped free-standing LNMAS coatings can be well preserved even after 400 h aging. In thermal cyclic fatigue test, LNMAS-2 and LNMAS-3 coatings undertake thermal cycling lifetime of similar to 181 and 191 cycles at 1100 degrees C, respectively, 40% durable than that of LMA coating. These preliminary results suggest that LNMAS-2, 3 might be promising candidates for advanced thermal barrier coating applications.

LaMgAl11O19-type magnetoplumbite holds great promise to be used above 1300 degrees C as thermal barrier coatings (TBCs), but its practical application has been restricted because of inferior thermophysical properties. Herein, we focus on optimizing the thermophysical properties of LaMgAl11O19 by simultaneously substituting La3+ and Al3+ ions with Nd3+ and Sc3+ ions, respectively. Results show that the effects of co-substitution on reducing thermal conductivity are pronounced. The thermal conductivities of La1-xNdxMgAl11-xScxO19 (x = 0, 0.1, 0.2, 0.3) ceramics decrease progressively with dopant concentration and a lowest thermal conductivity of 2.04 W/(m.K) is achieved with x = 0.3 at 1000 degrees C, which is a value superior to pure LMA and even lower than YSZ. The mechanisms behind the lowered thermal conductivity are investigated. Increase of the thermal expansion coefficient is also realized (8.53 x 10(-6) K-1 for pure LMA, 9.07 x 10(-6) K-1 for x = 0.3, 1300 degrees C). Most importantly, Nd3+ and Sc3+ combination doping indeed facilitates mechanical properties of La1-xNdxMgAl11-xScxO19 solid solutions as well. It should be noted that Sc3+ doping at Al3+ site plays more effective role in improving thermal properties than Nd3+ does at La3+ site. This work provides a path to simultaneously integrate low thermal conductivity, good phase stability, moderate thermal expansion behavior and excellent mechanical properties on LMA for the next generation TBCs.