THERMAL CYCLE FATIGUE PROPERTIES OF COATED AND UNCOATED SINGLE-CRYSTAL SUPERALLOY

In order to increase efficiency and power output of gas turbines, turb ine inlet temperatures are being steadily increased. To improve the su rface resistance of single crystal (SC) blades against oxidation and c orrosion, the base material is coated with MCrAlY type overlay coating s. In addition to the mechanical stresses, the coating are subjected t o thermal cycling which can result in fatigue cracking. Thermal cycle fatigue (TCF) properties are an important feature for selection of the system. In this paper we will present a TCF measuring method for a fa st screening of uncoated and coated materials. Based on the experience with polycrystalline IN 738 LC and single crystal materials (SC 16) w e will discuss TCF data. The cycles to crack initiation of coated SC i s strongly influenced by grain boundaries.