Characterisation of the microstructure and thermal properties of Nd2Zr2O7 and Nd2Zr2O7/YSZ thermal barrier coatings

The microstructure of following thermal barrier coatings (TBC) was characterised in this paper: monolayer coatings Nd₂Zr₂O₇ and 8YSZ; a double ceramic layered (DCL) coating. Coatings were characterised by thicknesses that did not exceed 300 μm and porosities of approx. 5%. The chemical and phase composition analysis of the DCL layers revealed an external Nd₂Zr₂O₇ ceramic layer approx. 80 μm thick, a transitional zone approx. 120 μm thick and an internal 8YSZ layer 100 μm thick. For the case of the monolayer coating, the Nd₂Zr₂O₇ pyrochlore phase was the only one-phase component. The surface topography of both TBC systems was typical for plasma sprayed coatings, and compressive stress state had a value of approx. 5–10 MPa. Measurements of the thermal parameters, i.e., thermal diffusivity, point to considerably better insulative properties for both new types of layers when compared to the standard 8YSZ layers.     

High-entropy thermal barrier coating of rare-earth zirconate: A case study on (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)2Zr2O7 prepared by atmospheric plasma spraying

We report a double-ceramic-layer (DCL) thermal barrier coating (TBC) with high-entropy rare-earth zirconate (HE-REZ) as the top layer and yttria stabilized zirconia (YSZ) as the inner layer sprayed on Ni-based superalloy by atmospheric plasma spraying. La₂Zr₂O₇ (LZ) was selected as a reference for the HE-REZ. Thermal cycling test results demonstrate that the HE-REZ/YSZ DCL coating exhibited obviously improved thermal stability when compared to the LZ/YSZ DCL coating. The reasons for the improvement of the thermal shock resistance are considered to be the anti-sinterability of the HE-REZ ceramics during the thermal cycling test attributed to the sluggish diffusion effect and as well as the better match in the coefficient of thermal expansion of HE-REZ coating with the YSZ inner layer. In addition, the HE-REZ coating maintains fluorite structure after thermal cycling test. This study makes one step forward in the development and application of high-entropy rare-earth zirconate ceramic thermal barrier coatings.     

Thermal cycling behavior and bonding strength of single-ceramic-layer Sm2Zr2O7 and double-ceramic-layer Sm2Zr2O7/8YSZ thermal barrier coatings deposited by atmospheric plasma spraying

The single-ceramic-layer (SCL) Sm₂Zr₂O₇ (SZO) and double-ceramic-layer (DCL) Sm₂Zr₂O₇ (SZO)/8YSZ thermal barrier coatings (TBCs) were deposited by atmospheric plasma spraying on nickel-based superalloy substrates with NiCoCrAlY as the bond coat. The mechanical properties of the coatings were evaluated using bonding strength and thermal cycling lifetime tests. The microstructures and phase compositions of the coatings were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The results show that both coatings demonstrate a well compact state. The DCL SZO/8YSZ TBCs exhibits an average bonding strength approximately 1.5 times higher when compared to the SCL SZO TBCs. The thermal cycling lifetime of DCL SZO/8YSZ TBCs is 660 cycles, which is much longer than that of SCL 8YSZ TBCs (150 cycles). After 660 thermal cycling, only a little spot spallation appears on the surface of the DCL SZO/8YSZ coating. The excellent mechanical properties of the DCL LZ/8YSZ TBCs can be attributed to the underlying 8YSZ coating with the combinational structures, which contributes to improve the toughness and relieve the thermal mismatch between the ceramic layer and the metallic bond coat at high temperature.     

Investigating the thermal,mechanical and thermal cyclic properties of plasma-sprayed Al2O3-7YSZ/7YSZ double ceramic layer TBCs

Double ceramic layer (DCL) TBCs consisting of a top 20 wt.% Al₂O₃-7YSZ layer and a bottom 7YSZ layer were desirably designed to achieve preferable performance while the thermal, mechanical and thermal cyclic properties were comprehensively investigated. Compared to the conventional 7YSZ TBCs, the thermal insulation properties of the DCL coating were significantly improved due to the increased oxygen vacancy concentration induced by Al₂O₃ addition while the thickness of the thermally grown oxides was diminished by the decreased oxygen diffusion rate. Furthermore, the improved fracture toughness of the DCL coating also prolonged the thermal cyclic life.     

Superposed structure of double-ceramic layer based on YSZ/LaMgAl11O19 thermal barrier coating

The superposed structure of double ceramic layer (SDCL) could be an effective means to develop long-life thermal barrier coating (TBC) at high temperatures. In this study, YSZ/LaMgAl₁₁O₁₉ TBC system with double-ceramic layer (DCL) and SDCL structures were prepared on nickel-based superalloy substrates by atmospheric plasma spraying. The thermal cycling behavior of the coatings was investigated using a furnace at 1000 °C and burner-rig facility at 1375 ± 25 °C on the coating surface. Results showed that the thermal cycle life of the SDCL structure was increased by 7.2% for the furnace and 13.2% for the burner-rig facility compared with that of the DCL structure. The relatively long thermal cycle life of the SDCL structure was attributed to the blocking of the propagation of cracks in the LMA layers by the YSZ ceramic layer and the release of residual thermal stresses by the formation of cracks in the LMA layers.     

Thermal cycling and hot corrosion behavior of a novel LaPO4/YSZ double-ceramic-layer thermal barrier coating

LaPO₄ powders were produced by a chemical co-precipitation and calcination method. The ceramic exhibited a monazite structure, kept phase stability at 1400?°C for 100?h, and had low thermal conductivity (~ 1.41?W/m?K, 1000?°C). LaPO₄/Y₂O₃ partially stabilized ZrO₂ (LaPO₄/YSZ) double-ceramic-layer (DCL) thermal barrier coatings (TBCs) were fabricated by air plasma spray. The LaPO₄ coating contained many nanozones. Thermal cycling tests indicated that the spallation of LaPO₄/YSZ DCL TBCs initially occurred in the LaPO₄ coating. The failure mode was similar to those of many newly developed TBCs, probably due to the low toughness of the ceramics. LaPO₄/YSZ DCL TBCs were highly resistant to V₂O₅ corrosion. Exposed to V₂O₅ at 700–900?°C for 4?h, La(P,V)O₄ formed as the corrosion product, which had little detrimental effect on the coating microstructure. At 1000?°C for 4?h, a minor amount of LaVO₄ was generated.     

Evaluation of stress distribution and failure mechanism in lanthanum–titanium–aluminum oxides thermal barrier coatings

LaTi₂Al₉O₁₉ (LTA) is one of the most promising materials for new thermal barrier coatings (TBCs) to fulfill the demand of advanced gas turbines owing to its high temperature stability and low thermal conductivity. In the present study, a finite element (FE) based numerical study has been carried out to investigate the stress distribution in LTA single layered coating system in comparison with traditional yttria stabilized zirconia (YSZ) TBC. Stresses in YSZ/LTA double ceramic layer TBC system are also determined and presented for comparative analysis. The thermal cycling effect is simulated by sequent increment in TGO thickness in a series of FE simulations. In-plane stresses (σ_xx), out-of-plane stresses (σ_yy) and shear stresses (σ_xy) are determined for all systems, and peak stress values are presented for quantitative comparison. Elastic strain energy stored in TGO of all systems is calculated from FE results for TBC structural integrity assessment. It has been found that maximum in-plane and shear stresses are lower in the double ceramic layer coating system than in the single layer ceramic coating system. However, peak axial tensile and compressive stresses in the double ceramic layer coating are very close or higher than those in the single layer topcoat. Calculation of elastic store energy shows that double ceramic layer TBC system may exhibit better stability as compared to single layer systems. Results are presented to explain the failure mechanism in LTA coatings.     

LZC/YSZ DCL TBCs by EB-PVD: Microstructure,low thermal conductivity and high thermal cycling life

Thermal barrier coatings (TBCs) with low thermal conductivity have triggered tremendous attention due to their promising application in the gas turbine engines. Albeit recent studies have investigated double ceramic layers (DCL) with pyrochlore (A₂B₂O₇) phase, it still remains a big challenge for controlling element content and investigating the relationship between the complex hierarchical architectures and their thermal performances. Here we describe a series of DCL La₂O₃-ZrO₂-CeO₂ (LZC)/Y₂O₃-stabilized ZrO₂ (YSZ) coating under different current of electron beam by electron beam-physical vapor deposition (EB-PVD). The formation of hierarchical architecture with feathery microstructure and intra-columnar have been investigated in detail. The DCL coatings achieve a high thermal cycling life and relatively low thermal conductivity at controlling current of electron beam from 1.0 A to 1.3 A. This work may open new opportunities to rationally design other promising TBCs.     

Hot Corrosion of Stabilized Zirconia Thermal Barrier Coatings and the Role of Mg Inhibitor

The 3–4 mol% yttria‐stabilized zirconia (YSZ) is widely used as a material for thermal barrier coating; however, the corrosive constituents present in fuel typically result in mechanical disintegration of YSZ coatings. The 3–4 mol% YSZ coatings with respective porosity of ~3% and ~22% have been undertaken with the objective to compare the hot corrosion behavior in air and sulfur‐rich atmospheres. The coatings are kept in contact with V₂O₅ + MgO powder mixture at 750°C for different dwell times of 24 and 76 h. The samples kept in air have shown intact YSZ layer for both the coatings, whereas a delamination of YSZ layer is observed for high porosity sample kept in sulfur‐rich atmosphere. XRD patterns of all the samples treated in sulfur‐rich atmosphere have indicated a phase transformation in YSZ from tetragonal to monoclinic. However, no such phase transformation has been found for samples treated in air. The V₂O₅‐induced hot corrosion attack on YSZ coating in air has been successfully inhibited by MgO, which forms a thermally stable Mg₃V₂O₈ compound. However, in sulfur‐rich atmosphere, MgO is partially consumed to form sulfates, which allows certain fraction of V₂O₅ to react with Y₂O₃ causing the degradation of top coat.     

Hot corrosion behaviour of atmospheric and solution precursor plasma sprayed (La0.9Gd0.1)2Ce2O7 coatings in sulfate and vanadate environments

Conventional and solution precursor plasma spraying (SPPS) techniques were employed for developing gadolinium oxide doped lanthanum cerate ((La_0.9Gd_0.1)₂Ce₂O₇, Gd-LC) based double-layered thermal barrier coatings (TBCs). Hot corrosion studies of the above coatings were carried out in molten Na₂SO₄ + V₂O₅ (1:1) environment at 900 °C. The state-of-the-art yttria-stabilized-zirconia (YSZ) coating was found to be completely delaminated after 120 h by forming yttrium vanadate (YVO₄) and m-ZrO₂. The accelerated delamination of YSZ can be attributed to the undesired phase transformation during exposure to corrosive species. Double-layered APS coatings were found to last for more than 300 h without densification of underlying YSZ layer and also, show better adherence with bond coat. SPPS Gd-LC coatings were found to be completely delaminated on densifying the underlying YSZ within 300 h. Lanthanum vanadate (LaVO₄) was found to be the main corrosive product along with minor amounts of gadolinium vanadate (GdVO₄) in Gd-LC double-layer coatings.     

Corrosion behavior of air plasma spraying zirconia-based thermal barrier coatings subject to Calcium–Magnesium–Aluminum-Silicate (CMAS) via burner rig test

Three different kinds of thermal barrier coatings (TBCs) — 8YSZ, 38YSZ and a dual-layered (DL) TBCs with pure Y₂O₃ on the top of 8YSZ were produced on nickel-based superalloy substrate by air plasma spraying (APS). The Calcium–Magnesium–Aluminum-Silicate (CMAS) corrosion resistance of these three kinds of coatings were researched via burner rig test at 1350 °C for different durations. The microstructures and phase compositions of the coatings were characterized by SEM, EDS and XRD. With the increase of Y content, TBCs exhibit better performance against CMAS corrosion. The corrosion resistance against CMAS of different TBCs in descending was 8YSZ + Y₂O₃, 38YSZ and 8YSZ, respectively. YSZ diffused from TBCs into the CMAS, and formed Y-lean ZrO₂ in TBCs because of the higher diffusion rate and solubility of Y³⁺ in CMAS than Zr⁴⁺. At the same time, 38YSZ/8YSZ + Y₂O₃ reacts with CAMS to form Ca₄Y₆(SiO₄)₆O/Y_4·67(SiO₄)₃O with dense structure, which can prevent further infiltration of CMAS. The failure of 8YSZ coatings occurred at the interface between the ceramic coating and the thermally grown oxide scale (TGO)/bond coating. During the burner rig test, the Y₂O₃ layer of the DL TBCs peeled off progressively and the 8YSZ layer exposed gradually. DL coatings keep roughly intact and did not meet the failure criteria after 3 h test. 38YSZ coating was partially ablated, the overall thickness of the coating is thinned simultaneously after 2 h. Therefore, 8YSZ + Y₂O₃ dual-layered coating is expected to be a CMAS corrosion-resistant TBC with practical properties.     

Microstructural characterization of GZ/CYSZ thermal barrier coatings after thermal shock and CMAS+hot corrosion test

In this study, first, Gd₂Zr₂O₇/ceria–yttria stabilized zirconia (GZ/CYSZ) TBCs having multilayered and functionally graded designs were subjected to thermal shock (TS) test. The GZ/CYSZ functionally graded coatings displayed better thermal shock resistance than multilayered and single layered Gd₂Zr₂O₇ coatings. Second, single layered YSZ and functionally graded eight layered GZ/CYSZ coating (FG8) having superior TS life time were selected for CMAS + hot corrosion test. CMAS + hot corrosion tests were carried out in the same experiment at once. Furthermore, to generate a thermal gradient, specimens were cooled from the back surface of the substrate while heating from the top surface of the TBC by a CO₂ laser beam. Microstructural characterizations showed that the reaction products were penetrated locally inside of the YSZ. On the other hand, a reaction layer having ∼6 μm thickness between CMAS and Gd₂Zr₂O₇ was seen. This reaction layer inhibited to further penetration of the reaction products inside of the FG8.     

Thermal cycling behaviour of plasma sprayed lanthanum zirconate based coatings under concurrent infiltration by a molten glass concoction

Thermal barrier coatings (TBCs) used in gas-turbine engines afford higher operating temperatures, resulting in enhanced efficiencies and performance. However, during aero engine operation, environmentally ingested airborne particles, which includes mineral debris, sand dust and volcanic ashes get ingested by the turbine with the intake air. As engine temperatures increase, the finer debris tends to adhere to the coating surface and form calcium magnesium alumino-silicate (CMAS) melts that penetrate the open void spaces in the coating. Upon cooling at the end of an operation cycle, the melt freezes and the infiltrated volume of the coating becomes rigid and starts to spall by losing its ability to accommodate strains arising from the thermal expansion mismatch with the underlying metal. The state-of-the-art ZrO₂-7-weight% Y₂O₃ (YSZ) coatings are susceptible to the aforementioned degradation. Rare-earth zirconates have generated substantial interest as novel thermal barrier coatings (TBC) based primarily on their intrinsically lower thermal conductivity and higher resistance to sintering than YSZ. In addition, the pyrochlore zirconates are stable as single phases at up to their melting point. La₂Zr₂O₇ (LZ) is one among such candidates. Hence, the present study focusses on the comparison of cyclic molten CMAS infiltration behaviour of the base metal Inconel 738 (BM), the bond coat NiCrAlY (BC), the duplex YSZ, the LZ coating and a five layered coated specimen with LZ as top layer. Among those coatings mentioned above, the five layer coated specimen showed excellent CMAS infiltration resistance under thermal cycling conditions.     

Thermal shock behavior of 8YSZ and double-ceramic-layer La2Zr2O7/8YSZ thermal barrier coatings fabricated by atmospheric plasma spraying

The single-ceramic-layer (SCL) 8YSZ (conventional and nanostructured 8YSZ) and double-ceramic-layer (DCL) La₂Zr₂O₇ (LZ)/8YSZ thermal barrier coatings (TBCs) were fabricated by plasma spraying on nickel-based superalloy substrates with NiCrAlY as the bond coat. The thermal shock behavior of the three as-sprayed TBCs at 1000 °C and 1200 °C was investigated. The results indicate that the thermal cycling lifetime of LZ/8YSZ TBCs is longer than that of SCL 8YSZ TBCs due to the fact that the DCL LZ/8YSZ TBCs further enhance the thermal insulation effect, improve the sintering resistance ability and relieve the thermal mismatch between the ceramic layer and the metallic layer at high temperature. The nanostructured 8YSZ has higher thermal shock resistance ability than that of the conventional 8YSZ TBC which is attributed to the lower tensile stress in plane and higher fracture toughness of the nanostructured 8YSZ layer. The pre-existed cracks in the surface propagate toward the interface vertically under the thermal activation. The nucleation and growth of the horizontal crack along the interface eventually lead to the failure of the coating. The crack propagation modes have been established, and the failure patterns of the three as-sprayed coatings during thermal shock have been discussed in detail.     

Hot corrosion resistance of air plasma sprayed ceramic Sm2SrAl2O7 (SSA) thermal barrier coatings in simulated gas turbine environments

Samarium strontium aluminate (Sm₂SrAl₂O₇-SSA) and Yttria-stabilized zirconia (YSZ) thermal barrier coatings (TBCs) were developed on NiCrAlY bond coated Inconel 718 superalloy substrate using air plasma spray process. The hot corrosion study was conducted in simulated gas turbine environments (molten mixtures of 50?wt% Na₂SO₄ + 50?wt% V₂O₅ and 90?wt% Na₂SO₄ + 5?wt% V₂O₅ + 5?wt% NaCl) for two different temperatures of 700 and 900?°C. A developed SSA TBCs showed about 8% and 22% lower lifetime at 700 and 900?°C, respectively than YSZ TBCs in 50?wt% Na₂SO₄ +?50?wt% V₂O₅ (vanadate). The hot corrosion life of SSA TBCs being found about 13% and 39% lower than YSZ TBCs in 90?wt% Na₂SO₄ +?5?wt% V₂O₅ +?5?wt% NaCl (chloride) at 700 and 900?°C, respectively. X-ray diffraction results showed the formation of SmVO₄, SrV₂O₆, and SrSO₄ as a major hot corrosion product in 50?wt% Na₂SO₄ +?50?wt% V₂O₅ and 90?wt% Na₂SO₄ +?5?wt% V₂O₅ +?5?wt% NaCl environments respectively for SSA TBCs. Similarly, YSZ TBCs also showed YVO₄ as hot corrosion product in vanadate and chloride environments. Both the TBCs suffer a more severe hot corrosion attack in chloride environment at 900?°C. The leaching of Sr²⁺ and Y³⁺ ions from SSA and YSZ respectively play a vital role in the destabilization of coating in vanadate and chloride environments at 700 and 900?°C. In both SSA and YSZ TBCs, the leaching of ion has significantly low influence as compared to attack by chloride ions at the bond coat-top coat interface in the presence of chloride environment. The hot corrosion resistance of SSA TBCs was improved three times higher in the presence of MgO and NiO inhibitor in vanadate environment at 900?°C mainly due to the formation of a stable Ni₃V₂O₈ phase at the surface.     

Study on thermal shock resistance of Sc2O3 and Y2O3 co-stabilized ZrO2 thermal barrier coatings

In order to reveal the effect of Sc₂O₃ and Y₂O₃ co-doping system on the thermal shock resistance of ZrO₂ thermal barrier coatings, Y₂O₃ stabilized ZrO₂ thermal barrier coatings (YSZ TBCs) and Sc₂O₃–Y₂O₃ co-stabilized ZrO₂ thermal barrier coatings (ScYSZ TBCs) were prepared by atmospheric plasma spraying technology. The surface and cross-section micromorphologies of YSZ ceramic coating and ScYSZ ceramic coatings were compared, and their phase composition before and after heat treatment at 1200 °C was analyzed. Whereupon, the thermal shock experiment of the two TBCs at 1100 °C was carried out. The results show that the micromorphologies of YSZ ceramic coating and ScYSZ ceramic coating were not much different, but the porosity of the latter was slightly higher. Before heat treatment, the phase composition of both YSZ ceramic coating and ScYSZ ceramic coating was a single T′ phase. After heat treatment, the phase composition of YSZ ceramic coating was a mixture of M phase, T phase, and C phase, while that of ScYSZ ceramic coating was still a single T′ phase, indicating ScYSZ ceramic coating had better T′ phase stability, which could be attributed to the co-doping system of Sc₂O₃ and Y₂O₃ facilitated the formation of defect clusters. In the thermal shock experiment, the thermal shock life of YSZ TBCs was 310 times, while that of ScYSZ TBCs was 370 times, indicating the latter had better thermal shock resistance. The difference in thermal shock resistance could be attributed to the different sintering resistance of ceramic coatings and the different growth rates of thermally grown oxide in the two TBCs. Furthermore, the thermal shock failure modes of YSZ TBCs and ScYSZ TBCs were different, the former was delamination, while the latter was delamination and shallow spallation.     

Isothermal oxidation and TGO growth behaviors of YAG/YSZ double-ceramic-layer thermal barrier coatings

In this study, yttrium aluminum garnet/yttria-stabilized zirconia (YAG/YSZ) double-ceramic-layer thermal barrier coatings (DCL TBC) and yttria-stabilized zirconia (YSZ) single-ceramic-layer thermal barrier coatings (SCL TBC) were deposited by atmosphere plasma spray (APS) on the Inconel 738 alloy substrate, and isothermal oxidation tests were performed to investigate the formation and growth behavior of thermally grown oxide (TGO). Results showed that the Al₂O₃ TGO thickness of both TBC groups increased by increasing the isothermal oxidation time，and then slowly decreased with the appearance and growth of the adverse multilayer structure comprising CoCr₂O₄, (Ni,Co)Al₂O₄, NiCr₂O₄, and NiO mixed oxides. However, since the significant inhibition effect of the YAG coating to oxygen ionic diffusion, the mixed oxides appearance time and TGO growth behaviors were delayed in the DCL TBC. As a result, the TGO thickness of the DCL TBC was always smaller than that of the SCL TBC in the entire oxidation process. And the Al₂O₃ layer thickness proportion in the total TGO of the DCL TBC was greater than or equal to that of the SCL TBC after oxidation for the same period. The results of weight gain showed that compared with the SCL TBC, the parabolic oxidation rate of the DCL TBC was decreased approximately 35%. Consequently, the DCL TBC has better high-temperature oxidation resistance than the SCL TBC.     

Comparison of hot corrosion behaviors of plasma-sprayed nanostructured and conventional YSZ thermal barrier coatings exposure to molten vanadium pentoxide and sodium sulfate

The purpose of the current study was evaluation and comparison of hot corrosion behaviors of plasma-sprayed conventional and nanostructured yttria stabilized zirconia (YSZ) thermal barrier coatings (TBCs). Hot corrosion studies were performed on the surface of coatings in the presence of a molten mixture of V₂O₅+Na₂SO₄ at 1000 °C for 30 h. Results indicated that the hot corrosion mechanisms of conventional and nanostructured YSZ coatings were similar. The reaction between corrosive salt and Y₂O₃ produced YVO₄, leaching Y₂O₃ from YSZ and causing the detrimental phase transformation of zirconia from tetragonal to monoclinic. The nanostructured coating, as compared to its conventional counterpart, in spite of a further reaction with the corrosive salt, showed a higher degradation resistance during the hot corrosion test due to increased compliance capabilities resulting from the presence of an extra source of porosity associated with the nano-zones.     

Fabrication of ceramic sealing coatings for shell bionic structures and their failure mechanism during thermal cycling

The porous ceramic coating as a "brick" layer sprayed by air plasma spraying(APS) and MK resin as a "mud" layer prepared by a high viscosity spray gun were characterized and tested. Three specifications of the "brick-mud" layered ceramic sealing coating were fabricated through the cyclic and orderly deposition of the "brick" layer and "mud" layer, and the thermal cycling performance and failure mechanism of the three new coatings were studied. The results showed that the agglomerated Y₂O₃ partially stabilized ZrO₂ (YSZ) particles had porous spherical structures and good sprayability, and the content of the YSZ phase in the prepared "brick" layer was 54.2%. The "mud" layer had good phase stability and was amorphous SiO₂ at and below 1100 °C. The fracture toughness of the pure YSZ coating was 2.295 ± 0.135 MPa?m^0.5, and which of the “mud” layer was reduced by 72.3%. The thermal cycling life of the conventional coating was only 67.3 times, which of A1, A2 and A3 coatings with 2, 3 and 6 "mud" layers were increased by 32.4%, 124.8% and 88.3%, respectively. In the thermal cycling process, the "weak" layer in the "brick-mud" layered coating led to the redistribution of internal stress and reduced the stress concentration in the top coating (TC)/TGO interface. Moreover, the initiation of microcracks in the "weak" layer, along with the "crack branching" effect and the "crack deflection" effect during the crack propagation process, could consume partial internal stress. Thus, the crack growth rates in the TC coating/TGO interface of the A1, A2 and A3coatings were lower than that of the conventional coating due to the above stress release mechanisms. In addition, the thermal cycling lives of the three new coatings with 2, 3 and 6 "mud" layers were improved to different degrees because of different stress effects.