High-cycle fatigue behaviour and crack growth mechanism of Ni-base single crystal superalloy under intermediate temperature

Abstract

This study investigates the high cycle fatigue behaviour of a Ni-base single crystal superalloy under 760 °C and 850 °C. At 760 °C, the crack initially grows in the crystallographic shearing mode and the crack tip propagation mechanism is non-crystallographic mode. Furthermore, near the crack tip propagated at 760 °C, the oxide film distributes along the γ/γʹ interface and the Ni-rich γʹ phase dissolution channels pass through the matrix in different ways, resulting in the wavy-like and dendritic cracks. When the temperature rises to 850 °C, recrystallization grains are observed in the fatigue initiation region. Moreover, the stress reduction leads to the increment of accumulative strain and the aggravation of the recrystallization. This will enhance the crack growth driving factor, promoting the crack to grow in crystallographic shearing mode. Finally, the mechanisms of high cycle fatigue crack growth influenced by temperatures and stresses are obtained and enhancement conditions of crack growth driving factor are revealed.