極微小SPクリープ試験片によるNi基超合金のクリープ強度評価

抄録

Dimensions of conventional Small Punch (SP) Creep specimen are 10 mm of diameter and 0.5 mm in thick, and this has been recognized as a standard SP creep specimen. However, this specimen sometimes had difficulties to evaluate creep rupture lives for local spots in discontinuities of structural components. Thus, very small punch creep specimen, almost half size of the standard one, is developed to overcome them. After the availability of new SP creep specimen was confirmed, new specimens were employed to evaluate the creep rupture lives for three small turbine wheels made of Nickel based super alloy. The alloy has a visible anisotropy in the microstructure due to unidirectional solidification; columnar dendroid. All tests were carried out at 720oC and the applied load of 150 N. SP creep rupture lives depend on the sampling area and dendrite arm spacing (DAS). Although the magnitude of DAS depended on the type of turbine wheel and the sampling spot, the creep rupture lives of specimens where the DAS is small are much longer.