Oxidation Localization Phenomena In Thermal Barrier Coatings System

Thermal Barrier Coatings (TBCs) is a kind of ceramic layer of excellent high temperature oxidation resistance as well as very low thermal conductivity, which is deposited onto the surface of substrate by the assistant of bond coat layer. TBCs can effectively reduce the service temperature of the protected substrate, alleviate the thermal shock loading, reduce the requirement for cooling air, and so, the thermal efficiency of apparatus is improved. Therefore, TBCs have been widely used in the fields of space flight, chemical industry, and metallurgy or energy sources industry.In high temperature service environment, the metallic element in bond coat is oxidized, and a layer of thermally grown oxide (TGO) is formed between ceramic top layer and bond coat layer, which mainly is consisted ofα-Al 2 O 3 because of its slow growth rate and good adherence capability. Impacted by creep and stress relaxation, the strain of bond coat layer increases irreversibly, and the TGO layer convolutes. If the TBCs system is homogeneous, the TGO will take on relatively regular and periodical undulation. Unfortunately, in actual situation, some abnormal thick areas will be presented in TGO, which is in single-layer or multi-layer form. In SEM, it can be seen that such protrusion areas originate from TGO, and penetrate into bond coat layer gradually with the increment of oxidation time, namely, the oxidation localization phenomenon occurs.This thesis is organized according to the following outline: firstly, the cause of oxidation localization was discussed in the view of material, both the microstructure and appearance of TGO were analyzed, the element composition of oxidation localization area was probed, combined with oxidation mechanism, the possible influence of oxidation localization on the mechanical performance of TBCs was discussed as well. Secondly, the evolution rule of oxidation localization area was investigated, according to experiment data, the influence resulted from different preparation processes and oxidation condition were explained, in particular, it was explored that the mechanism of oxidation localization under cyclic oxidation, and some preparation methods to reducing the harm of oxidation localization were introduced. Last, based on the rumpling mechanism of elastic film on elastic-plastic metal layer, the evolution of oxidation localization area was simulated numerically...