Fatigue Strength of Functionally Graded Thermal Barrier Ceramic Coatings Subjected to Thermal Cycling under Gradient Temperature

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Surface modification techniques, such as thermal barrier coatings and protective coatings are key technology to develop next generation advanced gas turbines. As a part of program to develop the high performance coating systems for advanced gas turbines, the high temperature strength of the advanced materials with surface modifications has been studied in this research program. The conclusions obtained are summarized as follows :(1) A new fatigue test machine which can simulate the service condition of turbine blades and vanes was successfully produced.(2) Thermal fatigue tests of conventional two-layr NFGM coating specimens and a functionally gradient material (FGM) coating specimens were carried out. Damage process of the functionally graded thermal barrier coatings during the thermal cycling was qualified. The degradation of thermal barrier function of the FGM was also qualified.(3) The effect of the functionally graded thermal barrier coatings on the thermal fatigue strength of the … More advanced materials with ceramic coatings surface damage strength was quantitatively evaluated by the thermal cycling test in vacuum.(4) The fatigue fracture of the Ni-base superalloy, IN 738LC,coated with the so-called M-Cr-Al-Y alloys by low pressure plasma spraying was studied and clarified at high temperature in vacuum condition, compared with that of the substrate alloy, IN 738LC.The fatigue crack propagation process was also made clear from the investigation employing the special equipment with cyclic loading stages which fit within the scanning electron microscope. Special focus was paod on the fatigue crack growth behavior in the coated layr and the dependence of the MCrAlY alloy systems, as well as near the interface.(5) The effect of aluminide coating on the high-cycle fatigue strengths of Ni-base superalloys was clarified at room temperature and 800 ﾟC in vacuum, in comparison with those of the substrates. Based on the measurement of a critical strain above which brittle cracking appeared at the aluminide coating, a simple method which can provide a reasonable estimation corresponding with the experimental life, was proposed. Less