Influence of Oxidation and Thermal Cycling on Bonding Strength of Thermal Barrier Coating at Elevated Temperature

通过实验和分析估算了热障涂层的断裂强度和粘接强度。该试样由两个圆柱体组成，这两个圆柱体彼此对接，并在其上构建了粘合涂层和热障涂层（TBC）。涂层在室温到900摄氏度的温度下，承受张力和扭转的双重载荷。在1100℃氧化处理后，在室温下检测涂层的强度和试样的粘接强度。实验结果表明：(1)涂层与基体界面处的脱粘面积在循环扭转加载开始时迅速增大，随着循环次数的增加逐渐减小，且脱粘速率保持恒定。最后，在涂层破裂前加速脱粘。(2)随着温度的升高，TBC在循环剪切荷载作用下的粘接强度显著降低。即在加载循环次数N=10^4时，在20℃时，脱粘引起的破坏应力为353.4[MPa]，在600℃时为168.8[MPa]，在900℃时为21.6[MPa]。(3)氧化后TBC的强度下降幅度大于TBC的粘接强度下降幅度。采用有限元法分析了界面脱粘区尖端的剪应力分布。估计了TBC在脱粘过程中应力强度因子K和奇异性参数λ的变化。结果表明，K值随脱粘程度的增加而减小，TBC的脱粘起动主要受界面剪切应力分布的K和X的影响，并根据K值预测了脱粘速率。

Fracture strength and adhesive strength of the thermal barrier coating were estimated experimentally and analytically. The specimen consists of two cylinders which are butted with each other and on which both of the bonding coat and the thermal barrier coating (TBC) is constructed. The coating is loaded with combined tension and torsion at room temperature to 900 degree centigrade. Also, after oxidation process at 1,100 degree centigrade, strength of the coating and the adhesive strength in the specimen were examined at room temperature.The obtained results in the experiments are as follows,(1) Debonded area occurred at the interface between the coating and the substrate increases quickly at the beginning of cyclic torsional loading and decreases gradually with the increase of number of cycle and the debonding rate keeps constant. Finally, the debonding were accelerated just before the coating break.(2) The adhesive strength of the TBC under the cyclic shear loading decreases much with a increase of temperature. That is, the failure stress caused by debonding at number of loading cycle N=10^4 are 353.4[MPa] at 20℃, 168.8[MPa] at 600℃, and 21.6[MPa] at 900℃.(3) The strength of the TBC decreases so much than the decrease in an adhesive strength of the TBC after the oxidation process.The shear stress distributions at the tip of the debonded area in the interface were analyzed by FEM analysis. Changes of the stress intensity factor K and the singularity parameter λ in the process of debonding of the TBC were estimated. It was found that the value K decreases with the increase of debonding and that the initiation of debonding of the TBC was dominated by K and X of a shear stress distribution at the interface and the rate of debonding was predicted corresponding to the K value.