热震中7YSZ热障涂层结构演变

Structure Evolution of 7YSZ Thermal Barrier Coating During Thermal Shock Testing

采用低温超音速等离子喷涂(LT-HVOF)在镍基高温合金基体上制备了Ni Co Cr Al YTa粘结层,使用大气等离子喷涂(APS)在粘结层上`制备了7wt%Y2O3-Zr O2(7YSZ)陶瓷层。基于动态试验即热震实验研究了粘结层的扩散氧化机制,探讨了陶瓷层的烧结及相变过程并观察了涂层的结构演变。实验结果表明:动态热循环下随着热震次数的增加,粘结层组元扩散氧化形成热生长氧化物(TGO)且厚度逐渐增加。此外,粘结层组元在温度梯度下沿陶瓷层内部裂纹向高温区扩散,最终在陶瓷层表面裂纹区域出现大量的金属氧化物,同时粘结层组元的扩散有助于陶瓷层的烧结,导致其显微硬度逐渐增大,而粘结层由于Kirkendall效应,其内部出现大量的孔洞导致其显微硬度逐渐降低。另外,陶瓷层在相变及热循环应力的作用下表面出现了大尺度的宏观裂纹。

Bond coating NiCoCrAlYTa was prepared on nickel-based superalloy by low temperature-high velocity oxygen flame （LT-HVOF）. Then 7wt% Y2O3 stabilized ZrO2 ceramic coating was fabricated on bond coating by air plasma spray （APS）. Diffusion principles of bond coating were investigated under thermal cycle by using multi-functional flame tester. Sintering and phase transformation of ceramic coating were studied. The experiment results show that with thermal cycle increase, thermally grown oxide （TGO） forms at the interface of ceramic-bond coating and its thickness continuously increases. Besides, the bond coating further diffuses to surface of ceramic coating. Lots of oxides appears on the surface of ceramic coating nearing microcrack. Diffusion of bond coating to surface contributes to sintering of ceramic coating, which leads to increase of microhardness. Additionally, plenty of voids were appeares in bond coating for Kirkendall effect resulting in decrease of microhardness. Large-scale cracks are observed after thermal cycle due to phase transformation and thermal residual stress.