稀土锆酸盐热障涂层材料的研究进展

稀土锆酸盐热障涂层材料具有耐高温、抗烧结、低导热、高温相结构稳定和抗腐蚀性能好等优点,被认为是最具有潜力的新型高温热障涂层材料体系之一.概述了目前关于这种热障涂层材料体系的晶体结构、物理性能、力学性能、抗热震性以及热腐蚀性等的研究进展,并进一步展望了稀土锆酸盐热障涂层材料的发展方向.     

新型热障涂层材料研究进展（英文）

热障涂层是高温下具有良好隔热性能的陶瓷涂层,在燃气轮机、内燃机、火箭发动机和其他高温热防护方面有重要应用。稀土或碱土金属氧化物稳定的氧化锆热障涂层材料已应用近60 a,其中最常用的是氧化钇稳定的氧化锆(YSZ)。近20 a,国内外发现了许多新材料,如稀土锆酸盐、铝酸盐和钽酸盐等。与YSZ相比,新材料在高温稳定性、热导率、抗烧结或热膨胀性能方面有优势,但断裂韧性低、成分复杂、单一陶瓷层的热循环寿命短。为了提高新型热障涂层的寿命,要严格控制涂层的制备过程、保持化学计量比,采用双陶瓷层结构的涂层。     

热障涂层研究进展

热障涂层由于具有优良的隔热、耐高温、抗氧化腐蚀以及抗磨损等性能,已应用于燃气轮机、航空发动机的高温镍基金属叶片的隔热保护。对热障涂层最新研究进展及发展趋势进行了论述,着重探讨了有关热障涂层的几种主要制备工艺,包括等离子喷涂、电子束物理气相沉积、高速火焰喷涂以及高频脉冲爆炸喷涂,对比分析了各自特点;并从制备工艺、相变、结构、抗氧化性能等方面对热障涂层的失效机制进行了分析。     

热障涂层高温失效的研究进展

热障涂层的高温失效问题是热障涂层材料研究的重要命题,本文对国内外学者在热障涂层高温失效试验、失效机制、失效的动态监测和寿命预测方面的研究进展进行了综述。热障涂层的失效主要源自涂层中存在的热生长氧化物(TGO)的失效,文中总结出了国内外学者对TGO研究的几个重点方面,以期为热障涂层的高温失效问题提供研究思路。     

热障涂层体系中各界面失效行为的研究进展

主要介绍了关于高温合金表面热障涂层体系中界面失效行为的研究进展,针对热障涂层中的基体/粘结层界面、粘接层/TGO界面和TGO/陶瓷层界面,进行了高温服役过程中的退化失效及结构演变行为分析,提出了影响热障涂层界面性能的研究重点和方向。     

稀土盐类热障/环境障涂层研究现状

随着航空航天等领域热端部件表面热障/环境障涂层的服役环境越来越恶劣，对涂层的性能要求显著提高，作为目前广泛应用的Y₂O₃部分稳定的ZrO₂(YSZ)材料，已经不能完全满足使用要求，所以开发新型兼具优异性能可用于高温环境的涂层材料日益重要。稀土盐类材料作为新型热障/环境障涂层材料，因其复杂的结构、低热导率和高热膨胀系数等优点，而被国内外学者广泛关注和研究。因此，综述了几种稀土盐类涂层材料的晶体结构、力学性能、热学性能，展望其发展前景。     

航空发动机燃烧室壁面“热斑”对热障涂层失效的影响

航空发动机燃烧室壁面热障涂层的脱落直接影响着相关部件使用寿命，其重要原因是“热斑”环境下涂层的局部烧结使得涂层内具有更复杂的应力状态，从而产生新的失效模式。采用ANSYS稳态流场与ABAQUS瞬态耦合对瓦片涂层系统进行分析，并借助断裂力学与实验方法对涂层的开裂规律进行表征，结果表明涂层具有升温350℃的“热斑”表面温度场与139 MPa的内部集中剪应力，并受此影响在“热斑”边缘区域优先发生以I型载荷为主导的面内复合型开裂失效。     

热障涂层材料研究进展

热障涂层材料广泛应用于发动机热端部件的热防护,能有效提高航空发动机热端 部件的工作温度和使用寿命。目前商用的热障涂层材料为氧化钇部分稳定氧化锆,但其在服役 温度高于 1200?C 时会发生相变而失效,难以满足新一代航空发动机对热障涂层的性能要求。因 此,寻找新型热障涂层材料及其服役性能研究一直是近年来的热点。本文综述了近年来氧化钇 稳定氧化锆、钙钛矿氧化物、烧绿石氧化物以及稀土硅酸盐材料的研究进展,并展望了热障涂 层材料的未来发展趋势。     

等离子喷涂金属基热障涂层的研究

简述了金属基热障涂层的结构设计，等离子喷涂层制造工艺特点，影响因素，以及热障涂层的应用。     

Graceful behavior during CMAS corrosion of a high-entropy rare-earth zirconate for thermal barrier coating material

The corrosion resistance to calcium-magnesium-alumino-silicates (CMAS) is critically important for the thermal barrier coatings (TBCs). High-entropy zirconate (La_0.2Nd_0.2Sm_0.2Eu_0.2Gd_0.2)₂Zr₂O₇ (HEZ) ceramics with low thermal conductivity, high coefficient of thermal expansion and good durability to thermal shock is expected to be a good candidate for the next-generation TBCs. In this work, the CMAS corrosion of HEZ at 1300°C was firstly investigated and compared with the well-studied La₂Zr₂O₇ (LZ). It is found that the HEZ ceramics showed a graceful behavior to CMAS corrosion, obviously much better than the LZ ceramics. The HEZ suffered from CMAS corrosion only through dissolution and re-precipitation, while additional grain boundary corrosion existed in the LZ system. The precipitated high-entropy apatite showed fine-grained structure, resulting in a reaction layer without cracks. This study reveals that HEZ is a promising candidate for TBCs with extreme resistance to CMAS corrosion.     

Corrosion resistance and thermal-mechanical properties of ceramic pellets to molten calcium-magnesium-alumina-silicate (CMAS)

Because gas turbine engines must operate under increasingly harsh conditions, the degradation of thermal barrier coatings (TBCs) by calcium-magnesium-alumina-silicate (CMAS) is becoming an urgent issue. Mullite (3Al₂O₃·2SiO₂) is considered a potential material for CMAS resistance; however, the performance of mullite in the presence of CMAS is still unclear. In this study, mullite and Al₂O₃–SiO₂ were premixed with yttria stabilized zirconia (YSZ) in different proportions, respectively. Porous ceramic pellets were used to conduct CMAS hot corrosion tests, and the penetration of molten CMAS and its mechanism were investigated. The thermal and mechanical properties of the samples were also characterized. It was found that the introduction of mullite and Al₂O₃–SiO₂ mitigated the penetration of molten CMAS into the pellets owing to the formation of anorthite, especially at 45 wt% mullite/55 wt% YSZ. Compared with Al₂O₃–SiO₂, mullite possesses a higher chemical activity and undergoes a faster reaction with CMAS, thus forming a sealing layer in a short time. Additionally, the thermal expansion coefficient, thermal conductivity, and fracture toughness of different samples were considered to guide the architectural design. Considering the CMAS corrosion resistance, thermal and mechanical performance of TBCs systematically, a TBC system with a multilayer architecture is proposed to provide a theoretical and practical basis for the design and optimization of the TBC microstructure.     

Comparative study on failure behavior of promising CMAS-resistant plasma-sprayed thermal barrier coatings in burner rig test with/without CMAS deposition

Along with continuous progress in inlet temperature of turbine engine, calcium-magnesium-aluminum-silicate (CMAS) deposition has become one of serious challenges for traditional yttria partially stabilized zirconia thermal barrier coatings at elevated temperature. Although lots of materials with superior CMAS resistance have been proposed, there is few comparative research on performance of corresponding coatings reported especially when subjected to thermal cycling and CMAS simultaneously. To this end, some coatings were prepared in present study, and thereafter failure behavior in condition of thermal cycling and thermal cycling-CMAS was systemically investigated and compared. Experimental results showed a varied lifetime and cracking behavior in thermal cycling test and thermal cycling-CMAS test, indicating that CMAS infiltration affected failure behavior of coatings. Besides, it was numerically found that CMAS penetration would lead to a promotion of thermal stress, which increased the tendency for cracking during thermal cycling. And the phenomenon that channel crack was the precondition of delamination crack was revealed.     

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.     

Crystallization behavior of CMAS and NaVO3+CMAS mixture and its potential effect to thermal barrier coatings corrosion

Calcium-magnesium-alumina-silicate (CMAS) and molten salt corrosion pose great threats to thermal barrier coatings (TBCs), and recently, a coupling effect of CMAS and molten salt has been found to cause even severer corrosion to TBCs. In this study, the crystallization behavior of CMAS and CMAS+NaVO₃ is investigated for potentially clarifying their corrosion mechanisms to TBCs. Results indicated that at 1000 °C and 1100 °C, CMAS was crystallized to form CaMgSi₂O₆, while at 1200 °C, the crystallization products were CaMgSi₂O₆, CaSiO₃ and CaAl₂Si₂O₈. The introduction of NaVO₃ in CMAS reduced the crystallization ability, and as the NaVO₃ content increased, glass crystallization occurred at a lower temperature, with crystallization products mainly consisting of CaAl₂Si₂O₈ and CaMgSi₂O₆. At 1200 °C, CMAS+10 wt% NaVO₃ was in a molten state without any crystallization, which suggested that NaVO₃ addition in CMAS could reduce its melting point, indicating enhanced penetration ability in TBCs and thus increased corrosiveness.     

Calcium-magnesium-alumina-silicate (CMAS) resistance characteristics of LnPO4 (Ln = Nd,Sm, Gd) thermal barrier oxides

Calcium-magnesium-alumina-silicate (CMAS) attack has been considered as a significant failure mechanism for thermal barrier coatings (TBCs). As a promising series of TBC candidates, rare-earth phosphates have attracted increasing attention. This work evaluated the resistance characteristics of LnPO₄ (Ln = Nd, Sm, Gd) compounds to CMAS attack at 1250 °C. Due to the chemical reaction between molten CMAS and LnPO₄, a dense, crack-free reaction layer, mainly composed of Ca₃Ln₇(PO₄)(SiO₄)₅O₂ apatite, CaAl₂Si₂O₈ and MgAl₂O₄, was formed on the surface of compounds, which had positive effect on suppressing CMAS infiltration. The depth of CMAS penetration in LnPO₄ (Ln = Nd, Sm, Gd) decreased in the sequence of NdPO₄, SmPO₄ and GdPO₄. GdPO₄ had the best resistance characteristics to CMAS attack among the three compounds. The related mechanism was discussed based on the formation ability of apatite phase caused by the reaction between molten CMAS and LnPO₄.     

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 performance of La2Ce2O7/50 vol.% YSZ composite thermal barrier coating with CMAS corrosion

La₂Ce₂O₇ (LC) is receiving increasing attention due to its lower thermal conductivity, better phase stability and higher sintering resistance than yttria partially stabilized zirconia (YSZ). However, the low fracture toughness and the sudden drop of CTE at approximately 350?°C greatly limit its application. In this study, the LC/50?vol.% YSZ composite TBC was deposited by supersonic atmospheric plasma spraying (SAPS). Compared to YSZ or double layered LC/YSZ coating, the thermal cycling life of LC/50?vol.% YSZ coating with CMAS attack increased by 93% or 91%. The latter possessed higher fracture toughness (1.48?±?0.26?MPa?m^1/2) than LC (0.72?±?0.15?MPa?m^1/2) and better CMAS corrosion resistance than YSZ owing to the formation of Ca₂(La_xCe_1-x)₈(SiO₄)₆O_6–4x with <001> orientation perpendicular to the coating surface. The sudden CTE decrease of LC was fully suppressed in LC/50?vol.% YSZ coating due to the change of temperature dependent residual stresses induced by YSZ.