Fatigue crack growth behavior of interface crack in thermal barrier coating

(1)制备了以钴基高温合金为基体、NiCoCrAlY粘结层和8wt%Y2O3-ZrO 2表面涂层的热障涂层试样。(2)为了进行金属粘结层与陶瓷面层沿着界面的疲劳裂纹扩展试验，研制了电火花加工引入起始缺口的专用夹具和试件。(3)界面裂纹可以成功地引入到缺口的前面，并且它沿着界面区域扩展，并合并到固有的孔隙中。(4)基于边界元分析结果，裂纹沿着面层与粘结层界面在I型和II型混合模式条件下扩展，混合模式比随裂纹扩展而变化。(5)异种材料界面处的裂纹沿着扩展行为受参数Ki控制，而均质材料混合模式下的裂纹扩展行为受参数K θ max控制。(6)随着顶涂层孔隙率的增加，杨氏模量降低，因此K值也降低。然而，由于裂纹扩展阻力也降低，因此将存在最佳孔隙率。

(1) Thermal barrier coated samples with Co-base super alloy substrate, NiCoCrAlY bond coat and 8wt%Y2O3-ZrO2 top coat were prepared.(2) In order to perform a test of fatigue crack growth along interface between metal bond coat layer and ceramic top coat layer, a special jigs and specimens with starter notch introduced by EDM were developed.(3) An interface crack could be successfully introduced ahead of the notch and it propagated along interface region with coalescing to inherent pores.(4) Based on the results of BEM analysis, A crack along the interface between top coat and bond coat layers propagates under mixed mode conditions of mode I and mode II and mix mode ratio varies with crack extension.(5) The crack growth behavior along the interface of dissimilar materials is controlled by the parameter Ki, while it under mix mode in homogeneous materials is controlled by the parameter K θ max.(6) With increasing porosity of the top coat, Young's modulus decreases and hence K-value also decreases. However, since crack growth resistance also decreases, there will be the optimum porosity.