Tensile Behavior of Long-term Aged Nickel-base Superalloy

The microstructural change of directionally solidified nickel-base superalloy which was aged at 900 degrees C for 1500 hours and tensile behavior at different temperatures were investigated by scanning electron microscope (SEM) and transmission electron microscope (TEM). gamma' phase of the alloy coarsens and rafts in the course of aged treatment. The driving force of rafting is the decrease of interface energy and elastic strain energy. The stress of aged alloy increases slightly with the testing temperature. This arises from a few dislocations shearing the gamma' precipitates. There is a peak stress value at 760 degrees C, which is attributed to the high strength of the gamma' phase, the homogeneous deformation structure, and dislocation-gamma' precipitate and dislocation-dislocation interactions. The stress then decreases rapidly with increased temperature. The low stress of the gamma' phase and gamma' rafting at high temperature contribute to the drop of alloy strength. The change of elongation is inverse to that of the stress.