Periodic Cracking of Thermal Barrier Coatings for Improved Interfactial Thermal Fracture Resistanace: Experiments and Analysis

陶瓷热障涂层在航空航天和飞机发动机、燃气轮机和柴油发动机等高温应用中具有提高效率、燃油经济性、耐久性和性能的潜力。在这些应用中，涂层受到不同的高温和温度梯度，这可能最终导致涂层分层和剥落。涂层表面裂纹的存在已被证明可以延长其寿命。此外，最近的实验和分析结果表明，在高表面温度和大温度梯度的厚涂层中，改变裂纹的周期和长度/厚度比可以减少界面裂纹的扩展。这些结果表明，通过在制造过程中引入周期性裂纹系统，可以减少使用中的界面裂纹。这开启了使用等离子喷涂生产的厚热障涂层的可能性，这将提供更大的热保护和更长的热负荷下的使用寿命，还提供了更大的设计灵活性和更低的加工成本。因此，提出的研究目标是：(a)了解热喷涂过程中引入的表面裂纹存在时，热障涂层界面裂纹在高热通量下的响应；(b)利用控制实验和分析模型，结合涂层在不同热边界条件下的随时间变化的材料行为，确定裂纹长度、周期性、厚度对界面热断裂的影响

9908187KokiniCeramic thermal barrier coatings offer the potential for improved efficiency, fuel economy, durability and performance in high temperature applications such as aerospace and aircraft engines, gas turbines and diesel engines. In these applications, the coatings are subjected to varying high temperatures and temperature gradients, which can ultimately result in delamination and spalling of the coating. The presence of surface cracks in the coating has been shown to increase its life. Furthermore, recent experimental and analytical results have shown that changing the periodicity and length/thickness ratio of such cracks can decrease interfacial crack propagation in thick coatings which are subjected to high surface temperatures and large temperature gradients. These results suggest that by introducing a periodic crack system during manufacture it should be possible to reduce interface cracking in service. This opens up the possibility of using thick thermal barrier coatings produced by plasma spraying, which would provide significantly greater thermal protection and longer life under thermal loads and also give greater design flexibility and reduced cost of processing. Thus, the objectives of the proposed research are: (a) to develop an understanding of the response of interface cracks in thermal barrier coatings subjected to high heat fluxes in the presence of surface cracks introduced during the thermal spray process; (b) to use controlled experiments and analytical models to determine the effects of crack length, periodicity, thickness, combined with time-dependent material behavior of the coating under different thermal boundary conditions on the thermal fracture of the interface.***