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.     

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.     

SiC纳米陶瓷粉末激光烧结成形试验研究

基于选择性激光烧结快速成型技术,利用CO2激光对纳米SiC粉体材料进行了激光烧结成型的试验.用X射线衍射、扫描电镜等分析了烧结层中纳米SiC的显微组织,同时对激光烧结过程及工艺参数的影响进行了探讨.研究结果表明,采用选择性激光烧结工艺参数,可以实现SiC陶瓷块体的烧结成型,烧结件内部组织保持纳米结构,材料晶粒尺寸基本不长大.烧结过程中SiC有分解反应,产生纳米Si和C.     

热障涂层(TBCs)高温氧化及熔盐腐蚀性能的研究

对ZrO2-8wt%Y2O3(YSZ)不同结构的热障涂层(TBCs)在1050℃、900℃进行氧化及腐蚀试验.结果表明,结合层中加入YSZ,增大了Ni16Cr8Al颗粒的表面积,氧化速率增加;结合层的氧化是TBCs性能下降的主要原因;在含硫的腐蚀环境下,面层中稳定组元Y2O3的分解析出,破坏了YSZ的稳定性,改变了面层的应力状态,导致TBCs早期破坏.     

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.     

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。     

Phase stability and thermal conductivity of RE2O3 (RE=La,Nd, Gd,Yb) and Yb2O3 co-doped Y2O3 stabilized ZrO2 ceramics

Y₂O₃ stabilized ZrO₂ (YSZ) has been considered as the material of choice for thermal barrier coatings (TBCs), but it becomes unstable at high temperatures and its thermal conductivity needs to be further reduced. In this study, 1 mol% RE₂O₃ (RE=La, Nd, Gd, Yb) and 1 mol% Yb₂O₃ co-doped YSZ (1RE1Yb–YSZ) were fabricated to obtain improved phase stability and reduced thermal conductivity. For 1RE1Yb–YSZ ceramics, the phase stability of metastable tetragonal (t′) phase increased with decreasing RE³⁺ size, mainly attributable to the reduced driving force for t′ phase partitioning. The thermal conductivity of 1RE1Yb–YSZ was lower than that of YSZ, with the value decreasing with the increase of the RE³⁺ size mainly due to the increased elastic field in the lattice, but 1La1Yb–YSZ exhibited undesirably high thermal conductivity. By considering the comprehensive properties, 1Gd1Yb–YSZ ceramic could be a good potential material for TBC applications.     

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.     

纳米陶瓷复合材料的制备方法

纳米陶瓷复合材料具有良好的力学性能和优越的高温性能等特性，是当今材料科学研究的重要课题。本文综合国内相关资料对纳米陶瓷昨合材料的制备方法作一简要评述，主要介绍纳米陶瓷复合粉体的制备方法和固体纳米陶瓷复合材料的烧结。