航空发动机用高温防护涂层研究进展

航空发动机热端部件服役环境恶劣,往往遭受机械载荷、高温、腐蚀、冲蚀等多种耦合作用。目前先进航空发动机热端部件无一例外地采用高温防护涂层以提高高温部件的使用温度,延长部件服役寿命,提高发动机效率。针对热端部件具体的服役环境特点,合理的设计和选择高温防护涂层体系对于提高发动机性能具有重要意义。文中对国内外近年来航空发动机热端部件的高温防护涂层设计、材料、制备工艺等方面进行了综述,展望了航空发动机用高温防护涂层的研究和应用发展趋势。     

Plasma-sprayed La2Ce2O7 thermal barrier coatings against calcium–magnesium–alumina–silicate penetration

As one of promising thermal barrier coating (TBC) candidates, La₂Ce₂O₇ (LC) has attracted increasing attention because of its low thermal conductivity and potential capability to be operated above 1250 °C. In this paper, the microstructure evolution and mechanical properties of the plasma-sprayed LC TBC with calcium–magnesium–alumina–silicate (CMAS) glassy deposits at 1250 °C were investigated. Due to chemical reaction between the CMAS deposits and LC coating, a dense sealing layer, mainly composed of Ca₂(La_xCe_1−x)₈(SiO₄)₆O_6−4x and CeO₂, was formed on the coating after heat-treatment at 1250 °C and effectively prevented CMAS from further penetration. The interaction layer had the micro-hardness of ∼10–12 GPa, relatively harder than the LC coating.     

激光表面改性对熔盐环境下热障涂层相稳定性和微观结构的影响

目的改善Y_2O_3部分稳定ZrO_2(YSZ)热障涂层的抗熔盐腐蚀性能。方法采用脉冲Nd:YAG激光系统对大气等离子喷涂YSZ热障涂层进行激光表面改性,优化激光参数,将喷涂态以及激光改性涂层在700℃和1000℃的V_2O_5熔盐下进行4 h热腐蚀实验。采用XRD、SEM和EDS表征腐蚀前后喷涂态和激光改性涂层的物相成分、微观结构和化学成分,通过计算热腐蚀后涂层表面的单斜(m)ZrO_2含量,分析激光改性对涂层相稳定性的影响。结果涂层表面的激光改性层呈现致密柱状晶结构并有一些贯穿的垂直裂纹。与原始涂层一样,改性层呈现亚稳态(t′)四方相。改性涂层在700℃腐蚀4h后,腐蚀产物为ZrV_2O_7、YVO_4和少量m-ZrO_2;在1000℃腐蚀4h后,腐蚀产物为m-ZrO_2和YVO_4。对未改性的YSZ涂层进行相同条件下的熔盐热腐蚀,其腐蚀产物种类与改性涂层相同,但是m-ZrO_2含量更高,表明更多的t'相受熔盐腐蚀而分解。结论激光改性可提高YSZ涂层中t'相的稳定性,使得涂层具有更好的抗熔盐腐蚀性能。然而,熔盐易沿垂直裂纹在改性层中渗入,不利于涂层的长期稳定性。     

电子束物理气相沉积YSZ热障涂层恒温氧化实验研究

利用电子束物理气相沉积法制备了YSZ热障涂层,并对其恒温氧化时涂层形貌、相组成的演化过程进行了研究.结果表明,YSZ热障涂层具有典型的柱状晶结构.沉积态时YSZ涂层为t/t’相.1100℃恒温氧化1200h后,YSZ涂层仍为t/t’相,未发现脱落.     

Microstructure and thermo-physical properties of yttria stabilized zirconia coatings with CMAS deposits

Yttria stabilized zirconia (YSZ) thermal barrier coatings (TBCs) are used to protect hot-components in aero-engines from hot gases. In this paper, the microstructure and thermo-physical and mechanical properties of plasma sprayed YSZ coatings under the condition of calcium-magnesium-alumina-silicate (CMAS) deposits were investigated. Si and Ca in the CMAS rapidly penetrated the coating at 1250 °C and accelerated sintering of the coating. At the interface between the CMAS and YSZ coating, the YSZ coating was partially dissolved in the CMAS, inducing the phase transformation from tetragonal phase to monoclinic phase. Also, the porosity of the coating was reduced from ∼25% to 5%. As a result, the thermal diffusivity at 1200 °C increased from 0.3 mm²/s to 0.7 mm²/s, suggesting a significant degradation in the thermal barrier effect. Also, the coating showed a ∼40% increase in the microhardness. The degradation mechanism of TBC induced by CMAS was discussed.     

带热障涂层镍基单晶高温合金的激光制孔研究

采用毫秒激光和皮秒激光在带热障涂层的镍基单晶合金上加工了气膜孔,对比研究了长脉冲与超短脉冲加工对热障涂层及金属基体孔壁形貌的影响。实验发现,波长1064 nm的毫秒激光在试样表面产生的能量密度直接影响到陶瓷层的加工。以2866 J/cm2的能量密度从陶瓷面加工,陶瓷面的熔化所需要的热积累时间长,热量会传导至高温金属,产生类似熔池的热影响;而从金属面加工则由于陶瓷是最后加工的材料,有足够的热积累时间熔化陶瓷涂层,从而直接打通小孔。当毫秒激光的能量密度提高至6369 J/cm2时,热量在涂层中的积累速度加快,陶瓷材料能够快速熔化,从而避免了金属基体先于陶瓷熔化的现象,同时,加工过程中熔化后的陶瓷会经过孔通道,从而出现附着在孔壁上的现象。采用皮秒激光加工陶瓷涂层仅需要能量密度达到32 J/cm2,皮秒激光旋切制孔是将小孔圆周上的材料全部剥蚀掉,直至孔打通,而孔内的材料会从孔中掉出。皮秒激光加工中产生的等离子体冲击力会引起涂层的开裂,由于热障涂层制备方法不同引起涂层中的裂纹方向有所不同,等离子喷涂制备的涂层为层状结构,裂纹易沿平行于表面方向生长,而EB-PVD制备的涂层为柱状晶结构,裂纹多出现在柱状晶的间隙。     

Comparison of corrosion behaviors and wettability of CMAS on Ta2O5-Y2O3 co-stabilized ZrO2 and YSZ thermal barrier coatings

High-temperature degradation of the plasma sprayed 16 mol% TaO_2.5 + 16 mol% YO_1.5 co-stabilized ZrO₂ (YTZ) and YSZ (7.6 wt% Y₂O₃-stabilized ZrO₂) coatings under calcium-magnesium-aluminon-silicate (CMAS) attack at 1200 °C and 1250 °C were comparatively investigated. Results indicated that the coatings were insensitive to the infiltration of CMAS after 10 h corrosion at 1200 °C. At 1250 °C, the entire YSZ cross-section completely failed and also underwent serious chemical corrosion after 3 h hot corrosion. Even after 10 h corrosion, the penetration depth of CMAS into the YTZ was only about 80 µm. For YTZ coating, the YTaO₄ stabilizer could not easily dissolve in CMAS and precipitated out of the YTZ crystal lattice owing to the strong chemical interaction between Ta⁵⁺ and Y³⁺. The wettability of CMAS on YTZ coating was worse than that on YSZ coating. Compared with YSZ coating, the YTZ coating showed better resistance to CMAS corrosion.     

Mechanical properties,thermal expansion performance and intrinsic lattice thermal conductivity of AlMO4 (M=Ta,Nb) ceramics for high-temperature applications

The vital thermo-mechanical properties of thermal and environment barrier coatings (TBCs/EBCs) include high hardness, low Young's modulus, matching thermal expansion coefficients (TECs) with substrate and low thermal conductivity. The effect of distortion degree of crystal structure on thermo-mechanical properties of AlMO₄ (M=Ta, Nb) ceramics are assessed in this work. AlMO₄ ceramics display modest TECs and no phase transformation is detected from room temperature to 1200?℃. The experiment thermal conductivity can be dropped further as the theoretical minimum thermal conductivity of AlTaO₄ and AlNbO₄ is 1.48?W?m^?1 K^?1 and 1.05?W?m^?1 K^?1, respectively. The temperature dependent phonon thermal diffusivity of AlMO₄ ceramics has been confirmed; the intrinsic lattice thermal conductivity is determined. The extraordinary thermo-mechanical properties make it clear that AlMO₄ ceramics are suitable for high-temperature applications.     

Improve durability of plasma-splayed thermal barrier coatings by decreasing sintering-induced stiffening in ceramic coatings

In this study, a newly-tailored plasma-sprayed (PS) yttria-stabilized zirconia (YSZ) ceramic coating towards enhanced strain tolerance and sintering resistance was developed to improve the durability of TBCs. The thermal shock life was found to be markedly prolonged by more than four times. Failure mechanisms and sintering behavior of the newly-structured and conventional TBCs were systematically investigated through microstructural and mechanical analyses. Conventional TBCs suffered a premature spallation due to rapid sintering-induced stiffening of the ceramic top coat. In contrast, the new coating exhibits an enhanced sintering resistance whereby preserving a good strain tolerance over time. Specifically, its elastic modulus after thermal exposure remains comparable to the as-sprayed states. The effect of ceramic top coat stiffness on cracking behavior of TBCs was clarified by a corresponding cohesive zone finite element modeling. This study provides a new option for improving TBCs durability and the results could benefit the increased integrity of TBCs.     

Thermal radiation and cycling properties of (Ca,Fe) or (Sr,Mn) co-doped La2Ce2O7 coatings

La₂Ce₂O₇ with low thermal conductivity as a potential candidate of thermal barrier coatings (TBCs) was co-doped with (Ca, Fe) or (Sr, Mn) in order to further improve its thermal radiation at high temperatures. The microstructure, chemical composition, infrared emission properties (reflection and absorption properties) and thermal cycling lifetime of the coatings were respectively investigated. The results revealed that La_2-xCa_xCe_2-xFe_xO₇₊δ and La_2-xSr_xCe_2-xMn_xO₇₊δ coatings had defected fluorite structure and their infrared emittances were much higher than that of the parent La₂Ce₂O₇. The superior infrared emission could be ascribed to the enhancement of the intrinsic absorption (electron transition absorption), free-carrier absorption and impurity absorption as well as lattice vibration absorption. However, the thermal cycling lifetime of La₂Ce₂O₇ coatings presented a reduction after the (Ca, Fe) or (Sr, Mn) substitution, primarily due to the decrease in the fracture toughness and the increase in the thermal conductivity.