Temperature effect on the low cycle fatigue behavior of a directionally solidified nickel-base superalloy

The effect of temperature on low cycle fatigue behavior of a directionally solidified nickel-base superalloy has been investigated from 550 to 850 °C. The fatigue life reached maximum at about 700 °C. The fracture modes can be divided into three types: crystallographic plane facets fracture (shear fracture) at low temperature region (<600 °C), mixed fracture mode at middle temperature region (600-700 °C) and non-crystallographic fracture (I type fracture) at higher temperature region (>700 °C). The dominant reason of the fracture mode transition with temperature is the deformation of the γ′ precipitated phase at different temperatures. The precipitated phase is sheared by dislocations which are restricted to the primary {111} slip planes at 600 °C. As the temperature increases, the deformation of γ′ precipitated phase becomes anomaly and some secondary precipitates can be observed in the matrix.