Dissolution of η phase and evolution of dynamically recrystallized grains in ATI 718Plus superalloy during hot compressive deformation

The dissolution mechanism of the eta-Ni3(Al0.5Nb0.5) phase during hot compression in Ni-based ATI718Plus superalloy has been investigated. The results indicate that with increasing deformation, the amount of dynamic recrystallization grains in the gamma matrix increases, and the dissolution of the eta phase tends to be accelerated. At the precipitation temperature of the eta phase of 950 degrees C, the eta phase area fraction decreased from 9.8% to 3.0% after deformation. The deformation promotes dislocation accumulation at the boundaries of the eta phase, developing into subgrains and then evolving into DRX grains due to subgrain rotation. With increased strain, the subgrain rotations and DRX grain growths result in extrusion and subsequent fracture of the eta phase. Due to strain incompatibility between the eta phase and gamma matrix, dislocation sustains are accumulated at their interfaces, which disrupts the eta/gamma semi-coherent interface, leading to localized amorphization and the decomposition of the eta phase. Furthermore, dislocation surrounding the eta phase can act as diffusion channels for solute elements, promoting the dissolution of the eta phase and resulting in the element concentration gradient distribution from the eta phase to the gamma matrix.