Microstructure optimization for higher strength of a new Fe-Ni-based superalloy

Tensile properties and deformation mechanisms of a Fe-Ni-based superalloy with different size of gamma ' precipitates obtained through varied aging time are investigated at 700 degrees C. The gamma ' phase size increases with aging time, the yield strength of the alloy increases first and then decreases, which is consistent with the change trend of critical resolved stress of deformation mechanism. The dominant deformation mode of the alloy with fine gamma ' phase is weakly-coupled dislocation pairs with slip bands, and then changes to Orowan looping at a gamma ' size of approxi-mately 30 nm, resulting in the occurrence of peak value of strength. As the gamma ' size is above 40 nm, the defor-mation mechanism is Orowan bowing along with stacking fault shearing, decreasing the yield strength of the alloy. When gamma ' size is between 30 nm and 40 nm, the dominant deformation mechanism is Orowan looping with strongly-coupled dislocation pairs and the fracture mode is intergranular. Intermediate temperature brittleness occurs in the secondary aging treated alloy with a gamma ' phase size of approximately 30 nm, which is attributed to the increase in critical resolved stress and strain localization caused by the transformation of tensile deformation mechanism, and stress concentration due to dislocation entanglement at grain boundary. The sub-aging state of the alloy used for advanced ultra-supercritical plants may be a good choice for obtaining simultaneously favorable strength and ductility.

Automated summary

The tensile properties and deformation mechanisms of a Fe-Ni-based superalloy were investigated at 700 degrees C with different sizes of gamma ' precipitates obtained through varied aging time. The yield strength of the alloy increased first and then decreased with the increase of aging time, which was consistent with the change of critical resolved stress of deformation mechanism. The dominant deformation mode changed from weakly-coupled dislocation pairs with slip bands to Orowan looping as the size of gamma ' precipitates increased, resulting in the occurrence of peak value of strength. When the gamma ' size was above 40 nm, the dominant deformation mechanism was Orowan bowing along with stacking fault shearing, decreasing the yield strength of the alloy. When the gamma ' size was between 30 nm and 40 nm, the dominant deformation mechanism was Orowan looping with strongly-coupled dislocation pairs and the fracture mode was intergranular. Intermediate temperature brittleness occurred in the secondary aging treated alloy with a gamma ' phase size of approximately 30 nm, which was attributed to the increase in critical resolved stress and strain localization caused by the transformation of tensile deformation mechanism, and stress concentration due to dislocation entanglement at grain boundary. The sub-aging state of the alloy used for advanced ultra-supercritical plants may be a good choice for obtaining simultaneously favorable strength and ductility.