Influence of Cast Dimension on Rotary Bending High Cycle Fatigue Properties of Single Crystal Superalloy

Samples of DD3 single crystal superalloy with different dimensions were cast in the directionally solidified furnace with high temperature gradient. The effect of cast dimension on the rotary bending high cycle fatigue (HCF) properties of the alloy was investigated at 800 °C in ambient atmosphere. SEM was used to examine the fracture surface and fracture mechanism of the alloy. The results show that the rotary bending HCF properties of the alloy decreases with increasing cast dimension. The cast dimension has little effect on the HCF fracture mechanism of the alloy. The HCF fracture mechanism of the alloy with different cast dimensions is all quasi-cleavage fracture. The fatigue cracks initiated on the surface or near the surface of the specimens. The crack would propagate along {111} octahedral slip planes. Typical fatigue arc and striation formed on fatigue crack steady propagation. The degeneration of HCF properties is due to the increase of dendrite arm spacing and size of γ’ phase particles and maximal microporosity.