等离子喷涂-物理气相沉积防护涂层及其失效机理研究进展

防护涂层在航空发动机和燃气涡轮发动机免受水氧腐蚀和盐雾侵蚀、耐高温、抗冲刷和服役寿命方面发挥着重要的作用。等离子喷涂-物理气相沉积（PS-PVD）技术以其大功率、喷射范围广、能够使粉末原料以气相甚至离子化和非视线沉积特性等特点被广泛应用在热/环境障涂层制备领域,形成的涂层具有沉积效率高、孔隙率较高、热导率低、应变容限高等特点。首先,对PS-PVD热障涂层的表面形貌、柱状晶特点和等离子射流特性进行了探讨。然后,讨论了PS-PVD YSZ热障涂层表面镀铝改性对涂层抗CMAS侵蚀、减少孔隙和裂纹、TGO的生成和提高热循环寿命方面的重要作用,结果表明表面镀铝能显著减少涂层表面孔隙、凹坑、微裂纹和熔融盐对于热障涂层的不利影响。其次,简要概述了近年来SiC_f/SiC CMCs代替镍基高温合金在航空发动机基体上抗高温高压和快速失效方面发挥的重要作用。SiC_f/SiC CMCs与T/EBCs的结合,有效延长了航空发动机的使用寿命,是我国航空事业的又一次重大突破。此外,重点介绍了PS-PVD非视线沉积特性和涂层阴影效应在涂层沉积方面这一特色,总结了TGO、残余应力、热膨胀失配、微裂纹和粗糙度是涂层失效的主要影响因素。最后,对PS-PVD技术未来在制备热/环境障涂层方面的前景进行了展望。     

3D numerical reconstruction and microstructure regulation of thermal barrier coatings for high temperature components of gas turbine

Thermal barrier coatings (TBCs) are being widely used in the high temperature components of gas turbine to protect the metal from high temperature damage and prolong the service life of gas turbine. The preparation process of TBCs is complex, and many control parameters will affect the microstructure of TBCs. Inhomogeneous microstructure changes caused by defects (such as cracks, erosion and corrosion pits) will occur under tough service conditions. In order to study the effect of the microstructure change on the thermal insulation and failure mechanism, it is necessary to construct the microstructure of TBCs under various working conditions. In this work, a new numerical pore-crack-particle microstructure reconstruction method (PCPMR) for porous media is proposed and used to reconstruct the three-dimensional (3D) microstructure of TBCs. In this method, characteristic parameters were extracted from the scanning electron microscope (SEM) images and the shape constraint factors of defects and the crack deformation rate as well as the particle deformation rate are introduced to control the morphologies of defects in porous TBCs. Then coatings with pores after preparation and coatings with defects during long-term services were reconstructed respectively. The features of coating microstructures reconstructed by this method are in good agreement with the real model obtained by SEM images. At the same time, the effective thermal conductivity of the coating with different porosities and segmentation cracks as well as the temperature distribution of the coating surface under different crack scales were analyzed in the reconstructed 3D TBCs samples. The calculated results are in good agreement with the measured data in the published literatures, which justify the reliability of the proposed PCPMR method.     

The corrosion behaviors of thermal barrier material of M-YTaO4 attacked by CMAS at 1250 °C

The corrosion of YSZ TBCs attacked by calcium–magnesium–aluminosilicate (CMAS) is a serious problem. Yttrium tantalite (YTaO₄), a new kind of potential thermal barrier ceramic material, was expected to replace the YSZ to manufacture the TBCs because of its great thermophysical characteristics. In this study, porous YTaO₄ ceramic pellets, instead of actual TBCs, were used to investigate the CMAS corrosion resistance at 1250 °C. Results indicated that CMAS couldn't cover the whole surface of YTaO₄ pellets homogeneously because of low wettability between liquid CMAS and YTaO₄, in addition, there was almost no reaction layer after 4 h reaction. The XRD results showed that M-YTaO₄, M′-YTaO₄, Ca₂Ta₂O₇ and Y₂Si₂O₇ were the main four phases after reaction and there was no phase containing the elements of Mg and Al. Compared with YSZ TBCs, this new kind of potential thermal barrier ceramic material showed well resistance to CMAS corrosion.     

An innovative model coupling TGO growth and crack propagation for the failure assessment of lamellar structured thermal barrier coatings

The failure of plasma-sprayed thermal barrier coating (TBC) is often caused by the coating spallation due to crack propagation. In this study, a new model with stacking lamellae is developed based on the cross-section micrograph to explore crack propagation behavior within the ceramic top coat (TC) during isothermal cycling. The dynamic growth process of thermally grown oxide (TGO) is simulated via material properties change step by step. The stress profiles in the lamellar model are first evaluated, and the pore and lamellar interface crack effects on the stress state are further explored. Then, the successive crack growth, linkage, and ultimate coating spallation process is simulated. The results show that the stress intensity in TC enhances with thermal cycling. Large stress concentration always occurs near the pore and lamellar interface crack, which can result in the incipient crack growth. Moreover, the lamellar interface crack also changes the stress distribution within the TC and at the TC/bond coat interface. The multiple crack propagation upon temperature cycling is explored, and the possible coalescence mechanism is proposed. The lamellar crack steadily propagates at the early stage. The crack length sharply increases before the occurrence of coating spallation. The simulated coat spalling path is in line with the experimental result. Therefore, the new lamellar model developed in this work is beneficial to further reveal coating failure mechanism and predict coating lifetime.     

Thermophysical properties of Yb2O3 doped Gd2Zr2O7 and thermal cycling durability of (Gd0.9Yb0.1)2Zr2O7/YSZ thermal barrier coatings

(Gd_1−xYb_x)₂Zr₂O₇ compounds were synthesized by solid reaction. Yb₂O₃ doped Gd₂Zr₂O₇ exhibited lower thermal conductivities and higher thermal expansion coefficients (TECs) than Gd₂Zr₂O₇. The TECs of (Gd_1−xYb_x)₂Zr₂O₇ ceramics increased with increasing Yb₂O₃ contents. (Gd_0.9Yb_0.1)₂Zr₂O₇ (GYbZ) ceramic exhibited the lowest thermal conductivity among all the ceramics studied, within the range of 0.8–1.1 W/mK (20–1600 °C). The Young's modulus of GYbZ bulk is 265.6 ± 11 GPa. GYbZ/YSZ double-ceramic-layer thermal barrier coatings (TBCs) were prepared by electron beam physical vapor deposition (EB-PVD). The coatings had an average life of more than 3700 cycles during flame shock test with a coating surface temperature of ∼1350 °C. Spallation failure of the TBC occurred by delamination cracking within GYbZ layer, which was a result of high temperature gradient in the GYbZ layer and low fracture toughness of GYbZ material.     

Thermal shock resistance and mechanical properties of La2Ce2O7 thermal barrier coatings with segmented structure

La₂Ce₂O₇ (LCO) is a promising candidate material for thermal barrier coatings (TBCs) application because of its higher temperature capability and better thermal insulation property relative to yttria stabilized zirconia (YSZ). In this work, La₂Ce₂O₇ TBC with segmentation crack structure was produced by atmospheric plasma spray (APS). The mechanical properties of the sprayed coatings at room temperature including microhardness, Young's modulus, fracture toughness and tensile strength were evaluated. The Young's modulus and microhardness of the segmented coating were measured to be about 25 and 5 GPa, relatively higher than those of the non-segmented coating, respectively. The fracture toughness of the LCO coating is in a range of 1.3–1.5 MPa m^1/2, about 40% lower than that of the YSZ coating. The segmented TBC had a lifetime of more than 700 cycles, improving the lifetime by nearly two times as compared to the non-segmented TBC. The failure of the segmented coating occurred by chipping spallation and delamination cracking within the coating.     

EB-PVD 热障涂层TGO中氧化物混合区的形成及其影响

研究了电子束物理气相沉积热障涂层在1150～30℃之间的循环氧化行为;分析了TGO中YSZ-Al2O3混合区的形成过程及其对TGO的生长与TBCs失效的影响.TGO的向外生长和TBC沉积时形成的YSZ细晶区是形成YSZ-Al2O3混合区的两个重要条件.YSZ-Al2O3混合区对TBCs失效的影响表现在加速TGO的生长和裂纹易在该混合区形成两方面.     

爆炸喷涂技术制备热障涂层的研究

采用爆炸喷涂技术在M38G合金上制备热障涂层，分析了涂层的结构，形貌，显微硬度，并对涂层的氧化性能进行了研究，结果表明，爆炸喷涂制备的热障涂层均匀，致密，高温氧化过程中，陶瓷层与粘结层界面处生成了连续的Al2O3膜，使TBCs具有良好的抗高温氧化性。     

Degradation of bond coat strength under thermal cycling—technical note

Degradation in bond strength of plasma-sprayed thermal barrier coatings under thermal cycling was evaluated by tensile adhesion tests. The bond strength and failure mode for two types of bond coat materials were examined. Two bond coats having the same substrate and top ceramic coat behaved differently due to differences in the thermal mismatch stress at an interface between the metallic bond coat and the ceramic top coat.     

等离子喷涂结构涂层研究

介绍了等离子喷涂的原理及特点；综述了等离子喷涂结构涂层的研究进展，包括耐磨涂层、热障涂层、耐蚀涂层；介绍了等离子喷涂结构涂层的复合处理技术；展望了等离子喷涂结构涂层的发展前景。