Fatigue crack growth behavior of interface crack in thermal barrier coating

(1)制备了钴基高温合金基材、NiCoCrAlY粘结层和8wt%Y_2O_3-ZrO_2顶层的热障涂层试件。(2)为了进行金属粘结层与陶瓷顶层之间的界面疲劳裂纹扩展试验，研制了一种特殊的夹具和带有起始缺口的电火花加工试件。(3)在缺口前成功地引入了界面裂纹，并沿界面区域向固有气孔扩展。(4)基于边界元分析的结果，在I型和II型复合模条件下，沿面层和粘结层界面的裂纹扩展，混合模比随裂纹扩展而变化.(5)沿异种材料界面的裂纹扩展行为由参数KI控制，而均匀材料在混合模式下的扩展行为由参数K_θ_(Max)控制.(6)随着面层孔隙率的增加，杨氏模数减小，K值也减小.然而，由于裂纹扩展阻力也减小，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.