Investigation on Material's creep strength variation among different locations of directional solidified turbine blades

In order to obtain higher creep strength, the Directional Solidification (DS) Nickel-based turbine blades have been widely used in aero engines, because this advanced casting technology can improve the blade's creep performance along the principal stress direction by forming columnar grains parallel to this direction. However, the grain structures at different regions of turbine blade are likely to be different, because the temperature field during casting process is affected by the different abrupt geometrical changes. Therefore, a variation in the creep performances at these regions is caused. To study the variation in creep strength among different regions of a DS turbine blade, this work designed and manufactured three types of DS specimens which have the geometry features of the platform, the shroud and the body part of DS turbine blade. Creep tests on these specimens were conducted under a stress level of 608MPa and temperature of 850°C. The creep rupture life of platform-like and shroud-like specimens are about 93% and 73% of that of the body-like specimen respectively, which support that there exists a certain variation of creep strength among different regions in a DS turbine blade. It is suggested that the material's creep strength variation among different locations of DS turbine blades should be considered in future turbine blade life design and prediction.