Optimization of fatigue property of ceramic coating for next-generation gas turbine

对一种PSZ/NiCrAlY等离子喷涂涂层进行了热冲击和热疲劳试验，并通过断裂力学分析对热疲劳断裂机理进行了估计。在此基础上，结合涂层的组成和显微组织确定了等离子喷涂隔热涂层的最佳工艺条件。对优化后的涂层进行了循环燃烧器加热试验，并对试验过程中的断裂进行了详细观察。在考虑断裂力学因素的基础上，确定了最佳工艺条件和微观组织形态，结果表明：(1)热冲击试验加热和冷却阶段的声发射信号不同，表明了裂纹的萌生和扩展。(2)梯度结构能有效延长热疲劳寿命。(3)在较小的热载荷作用下，梯度层中形成小裂纹，有效延长了热疲劳寿命。(4)在陶瓷涂层与NiCrAlY结合涂层之间插入氧化铝层，有效抑制了结合涂层的氧化，避免了燃气轮机实际工作环境中经常出现的氧化损伤，提高了陶瓷涂层的性能。该研究结果将在美国科罗拉多州举行的第五届功能梯度材料国际研讨会上发表。

Thermal shock and thermal fatigue tests of a PSZ/NiCrAlY plasma-spray coating were carried out, and with fracture mechanical analysis thermal fatigue fracture mechanisms were estimated. On the basis of this estimation an optimum processing conditions for the plasma spraying of the heat insulation coating were determined with reference to the composition profiles and microstructure of the coated film. The optimized coatings were subjected to the cyclic burner heating test, and a detailed observation on the fracture during testing. Along with the fracture mechanical consideration and optimum process conditions and microstructure morphology were worked out, as presented as follows : (1) Different AE signals were observed for heating and cooling period of the thermal shock testing, which indicated the crack initiation and their propagation. (2) Graded structure was found to be effective to prolong the thermal fatigue life. (3) Under a smaller thermal lord small crack was observed to form in the graded layer, which was found to be effective to prolong the thermal fatigue life. (4) Insertion of alumina layer between ceramic overcoat and NiCrAlY bond coat effectively suppressed the oxidation of the bond coat, and this will avoid the oxidation damage which is often observed in the actual working circumstance of the gas turbine, and will bring about high performance of the ceramic coatings. The obtained results will be presented at the 5th International Symposium on Functionally Graded Materials at Colorado, USA.