Fatigue crack growth behavior of interface crack in thermal barrier coating

(1)制备了co基高温合金衬底、NiCoCrAlY结合层和8wt%Y2O3-ZrO2面涂层的热障涂层样品。(2)为了进行金属结合层与陶瓷面层界面疲劳裂纹扩展试验，研制了电火花加工引入启动缺口的专用夹具和试样。(3)界面裂纹可以在缺口前方成功引入，并沿界面区域扩展，并与固有孔隙结合。(4)基于边界元分析结果，在I型和II型混合模态条件下，沿面涂层和粘结层界面的裂纹扩展，并且混合模态比随裂纹扩展而变化。(5)异种材料界面裂纹扩展受Ki参数控制，均匀材料混合模式下裂纹扩展受K θ max参数控制。(6)随着面漆孔隙率的增加，杨氏模量减小，k值也随之减小。然而，由于抗裂纹扩展能力也会降低，因此会出现最佳孔隙率。

(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.