Hot corrosion behavior of Y4Al2O9 ceramics for thermal barrier coatings exposed to calcium-magnesium-alumina-silicate at 1250 °C

The degradation of thermal barrier coatings (TBCs) by calcium-magnesium-alumina-silicate (CMAS) attack has become increasingly dramatic. Y₄Al₂O₉ ceramic, a new potential TBC candidate, has received an increasing attention. In this study, porous Y₄Al₂O₉ ceramic pellets, instead of actual TBCs, are used to investigate the CMAS corrosion resistance at 1250 °C. Results indicate that Y₄Al₂O₉ reacts with CMAS melt to form an impervious sealing layer mainly containing Ca-Y-Si apatite, which could mitigate CMAS further penetration. Once the sealing layer formed, further reaction would occur above the layer accompanying by the recession of sealing layer. This process is probably related to a solid state diffusion.     

Preparation of plasma sprayed nanostructured GdPO4 thermal barrier coating and its hot corrosion behavior in molten salts

Nanostructured GdPO₄ coatings, designed as the outer layer of double-ceramic-layer thermal barrier coatings (DCL-TBCs), were produced by air plasma spraying (APS). The coatings have close chemical composition to that of the agglomerated particles used for thermal spray. Nanozones with porous structure are embedded in the coating microstructure, having a percentage of ~30%. Hot corrosion tests of the coatings were carried out in V₂O₅ and Na₂SO₄+V₂O₅ salts at 900 °C for 4 h. Results indicate that dense reaction layers, consisting of GdVO₄ and Gd₄(P₂O₇)₃, form on the coating surfaces, which could suppress further penetration of the molten salts. In the V₂O₅ molten salt, the reaction layer is thicker and less molten salt trace could be found beneath the layer.     

等离子喷涂双相复合结构顶层热障涂层的研究

热障涂层 (TBCs) 是燃气轮机等设备的高温部件上不可缺少的防护技术。 La2Zr2O7 是最具潜力的顶层材料, 但其韧性差等问题限制了其应用。 本研究采用双相复合陶瓷技术对 La2Zr2O7 进行改性, 以 LaPO4 与 La2Zr2O7 的 双相复合材料为热障涂层顶层材料。 采用机械混合和喷雾造粒技术制备双相陶瓷材料, 利用等离子喷涂的方法制 备双相陶瓷顶层。 通过热循环和冲蚀实验检测双相复合涂层的性能。 利用 X 射线衍射仪 (XRD) 检测涂层的相结构, 利用扫描电镜(SEM)检测涂层的表面和剖面形貌。结果表明, 双相复合结构涂层表面微细裂纹增多, 粗大裂纹减少, 裂纹会产生曲折和分叉。 LaPO4 的加入提高了双相陶瓷材料的韧性和断裂强度, 和单相 La2Zr2O7 涂层相比, 双相 陶瓷涂层在冲蚀过程中失重较少。     

Precipitation phases in the nickel-based superalloy DZ 125 with YSZ/CoCrAlY thermal barrier coating

Interdiffusion behavior of the thermal barrier coating (TBC) with the CoCrAlY bond coat (BC) and directionally solidified Ni-based superalloy DZ 125 was investigated. Severe inward-diffusion of Al, Co and Cr from the BC to the superalloy and outward diffusion of Ni and refractory elements such as W from the superalloy occur during annealing at 1050 °C in air. After 100 h annealing, a ∼30 μm thick inter-diffusion zone (IDZ) forms between the BC and superalloy, and a ∼35 μm thick secondary reaction zone (SRZ) forms beneath the IDZ. The IDZ mainly consists of β phase and γ matrix. Besides, small amount of Ta and Hf containing carbides are also observed in the IDZ. Needle and fine granular topologically close-packed (TCP) phases, characterized as rhombohedral μ phases, are abundant in the SRZ. The formation of SRZ is mainly due to the precipitation of refractory elements such as W and Mo from the γ matrix and β phase. The formation mechanism of SRZ and μ-TCP phase is discussed.     

Oxidation failure of TBC systems: An assessment of mechanisms

The spallation of thermal barrier coatings can be life-limiting but its prediction has proven to be a difficult problem. The final spallation event can often occur by buckling and is driven by the release of strain energy within the ceramic top coat and within the underlying thermally-grown oxide (TGO) layer if the delamination interface is at the TGO/bond-coat interface. Prior to this event, substantial sub-critical damage must develop at one or both of the TGO interfaces. It is argued in this paper that it is only the strain energy within the TGO produced during cooling that contributes significantly to this damage development and not that within the top coat. A critical strain energy within the TGO layer is suggested as a possible pragmatic method of predicting spallation. A critical assessment of proposed mechanisms which implicate bond coat oxidation in the failure process is also undertaken in the paper. Attention is given to: the role of phase changes in the bond coat; the influence of the mechanical constraint imposed by the top coat on the mechanical stability of the bond coat interface; the effect of the growth of the TGO on a non-planar interface on stress development; the importance of localised Al depletion in nucleating a fast-growing non-protective TGO.     

Synergistic effect between nano-ceramic lubricating additives and electroless deposited Ni-W-P coating

The major solving ways for the material wear are surface modification and lubrication.Currently,the researches at home and abroad are all limited to the single study of either nano-lubricating oil additive or electroless deposited coating.The surface coating has high hardness and high wear resistance,however,the friction reduction performance of the coating with high hardness is not good,the thickness of the coating is limited,and the coating can not regenerate after wearing.The nano-lubricating additives have good tribological performance and self-repair function,but under heavy load,the self-repair rate to the worn surface with the nano-additives is smaller than the wearing rate of the friction pair.To solve the above problems,the Ni-W-P alloy coating and deposition process with excellent anti-wear,and suitable for industrial application were developed,the optimum bath composition and process can be obtained by studying the influence of the bath composition,temperature and PH value to the deposition rate and the plating solution stability.The tribological properties as well as anti-wear and friction reduction mechanism of wear self-repair nano-ceramic lubricating additives are also studied.The ring-block abrasion testing machine and energy dispersive spectrometer are used to explore the internal relation between the coating and the nano-lubricating oil additives,and the tribology mechanism,to seek the synergetic effect between the two.The test results show that the wear resistance of Ni-W-P alloy coating(with heat treatment and in oil with nano-ceramic additives) has increased hundreds times than 45 steel as the metal substrate in basic oil,the friction reduction performance is improved.This research breaks through the bottleneck of previous separate research of the above-mentioned two methods,and explores the combination use of the two methods in industrial field.     

纳米陶瓷粉体的应用现状与展望

纳米陶瓷粉体在精细陶瓷、功能陶瓷、生物陶瓷及精细化工材料等高技术领域中得到了广泛的应用,已成为当今发展高技术材料的基石.分析纳米陶瓷粉体的应用研究现状,对研究其发展前景具有重要的现实意义.     

Effects of heat treatment on adhesion strength of thermal barrier coating systems

Thermal barrier coatings (TBCs) are widely used as protective and insulative coatings on hot section components of gas turbines and their applications, like blades and combustion chambers. The quality and performance properties of TBCs are of great importance in terms of their resistance to service conditions. In a TBC system, there is a close relationship between the adhesion properties of coating layers. The adhesion strength of TBCs varies depending on the coating technique used and the surface treatments. In this study, CoNiCrAlY and YSZ (ZrO₂ + Y₂O₃) powders were deposited on stainless steel substrate. High Velocity Oxy-Fuel (HVOF) and Atmospheric Plasma Spraying (APS) techniques were used to produce the bond coats. The ceramic top layers on CoNiCrAlY bond coats were produced by the APS technique. The TBC specimens were subjected to heat-treatment tests. Adhesion strength for top coat/bond coat interface of as-sprayed and heat-treated samples was investigated. The results showed that the heat treatment of the coatings in different temperatures led to an increase in the adhesion strength of TBCs.     

热障涂层隔热性能测试方法分析

分别利用4种不同的隔热性能测试方法,对氧乙炔火焰喷涂工艺制备的ZrO2陶瓷热障涂层的隔热性能进行了测试,通过红外测温仪和热电偶连接温度记录仪两种不同方式,测试试样金属基体温度,获得4组不同涂层厚度试样金属基体的温度变化曲线,并结合陶瓷涂层的服役工况对测试结果进行了分析,结果表明,测试方法不同,隔热性能测试所得数据也有所差异,但这4种测试方法均可不同程度的反映热障涂层的隔热效果及变化趋势,在接近实际服役工况条件下,可定性评估涂层隔热性能。     

考虑孔隙细观特征的热障涂层脱粘缺陷超声检测数值模拟

为探究孔隙细观形貌对热障涂层脱粘缺陷超声检测定量精度的影响,基于电子束物理气相沉积法制备的厚度约为100μm的ZrO_2-7%Y_2O_3(7YSZ)热障涂层SEM形貌,建立了界面脱粘尺寸0.2~2.0 mm、孔隙率范围0%~5%、孔隙平均宽高比分别为4∶10、6∶10、8∶10和10∶10的多组热障涂层二维随机孔隙模型(Random void model,RVM),采用时域有限差分技术进行了超声检测数值模拟。结果表明:当涂层厚度一定时,涂层声压反射系数幅度谱极值与脱粘尺寸呈线性关系,脱粘尺寸超声定量误差随孔隙率和孔隙平均宽高比的增加而增大,当涂层孔隙率为5%时,超声测量最大相对误差已达到37.7%,孔隙平均宽高比增大为10:10时,超声测量最大相对误差达到36.9%。此外,由于受孔隙分布状态的影响,超声定量结果呈现出一定的波动性。