Dissolution of γ' Phase in a Single Crystal Superalloy After High-cycle Fatigue

High-cycle fatigue (HCF) tests at different temperatures were performed on a single crystal superalloy SRR99 with [001] orientation. The results demonstrate that conditional fatigue strength increases first and then decreases with the increase of temperature, exhibiting the same tendency with tensile strength at elevated temperatures. The microstructures were observed by SEM and TEM and it is found that the morphology of gamma' particles changes significantly and dissolution of gamma' particles takes place during cyclic loading. This may be induced by the back and forth movement of interface dislocations during the cyclic loading. As a result, the strengthening effect of the coherent gamma/gamma coherent interfaces is gradually deteriorated during high-cycle fatigue deformation. In addition, the fatigue crack propagation is found to be primarily along a specific crystalline plane, which is identified as (111). The specific mechanism for the microstructure evolution during cyclic loading was discussed based on SEM and TEM observations.