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

对热障涂层的断裂强度和结合强度进行了实验和分析估算。试件由两个对接的圆柱体组成，其上既有粘结层又有热障涂层。涂层在室温至900 ℃范围内承受拉伸和扭转的复合载荷。另外，在1,100 ℃下进行氧化处理后，在室温下检查涂层的强度和试样中的粘合强度。（一）涂层与基体界面处的脱粘面积在循环扭转载荷作用初期迅速增大，随着循环次数和脱粘量的增加而逐渐减小速率保持恒定。最后，在涂层破裂之前加速剥离。(2)在循环剪切载荷作用下，TBC的粘结强度随温度的升高而降低。也就是说，在载荷循环次数N=10^4时，由剥离引起的破坏应力在20℃时为353.4[MPa]，在600℃时为168.8[MPa]，在900℃时为21.6[MPa]。(3)氧化处理后，热障涂层强度的下降幅度大于其粘结强度的下降幅度。采用有限元方法分析了界面脱粘区尖端的剪应力分布。估算了TBC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，脱粘的发生受界面剪切应力分布的K和X的影响，脱粘速率与K值相对应。

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.